School Science Lessons
2024-04-10
Weather science, climate change, gobal warming
(UNPh37.1) Contents
37.1.0 Environmental issues
37.2.0 Weather science
37.1.0 Environmental issues
37.1.3 Global warming and climate change
37.1.2 Coal seam gas, CSG, and coal to liquid, CTL
37.1.4 Oil shale and fracking
37.1.5 Fracking, by Josie Garthwaite, San Francisco (edited)
37.1.6 Protecting the Great Barrier Reef
37.2.0 Weather science
Experiments
Make weather instruments and a weather station.
Study of weather is a topic that is close to the life of every student.
Even at the lowest levels of primary instruction, you may make observations of the weather from day to day.
At the intermediate levels you may construct a simple weather station.
At the level of general science and later, you may study the causes of weather phenomena.
At all stages of the work it is an advantage to represent readings and observations in graphical form.
Weather science
37.2.1 Cold air is heavier than warm air, inverted paper bag balance, (Experiment)
37.2.2 Composition of the atmosphere and greenhouse gases
37.2.3 Convection box, smoke house, (Experiment)
37.2.4 Direction of water through a bath plug hole, (Experiment)
37.2.5 Coriolis, Trade winds and weather rotations
37.2.5a Trade winds and weather rotations, (Experiment)
37.2.6 Greenhouse effect in a model greenhouse
37.2.6a Greenhouse effect in a model greenhouse, (Experiment)
37.2.7 Height values, sea level
37.2.8 Hot air rising
37.2.9 Inversion layers
37.2.9a Inversion layers, (Experiment)
37.2.10 Layers of the atmosphere, lapse rate, auroras
37.2.11 Navigation data used by a ship at sea
37.2.12 Ocean iron fertilization
37.2.13 Storm glass
37.2.14 Trade winds, easterlies and westerlies
37.2.15 Warm fronts and cold fronts
37.2.16 Weather maps (synoptic charts), Buys Ballots law, geostrophic wind and gradient wind
37.2.17 Weather pictures, (Experiment)
37.2.18 Weather periods
37.2.19 Weather records, (Experiment)
37.2.20 Weather sayings
37.1.2 Coal seam gas, CSG, and coal to liquid, CTL
CSG, coal seam gas, is natural gas.
It is a mixture of mainly methane and other hydrocarbon gas compounds.
It is bonded to microscopic surfaces, the cleats or fractures in coal, so it is adsorbed to the coal by burial pressure and water.
To extract the gas, many holes are dug into the coal seams.
The quality of the water, a byproduct of the drilling, ranges from potable to saline and other constituents.
The coal seam gas industry is likely to drill up to 40 000 wells in Queensland by 2030, taking a minimum one hectare each of prime agricultural land each.
Recent expansion of interest in coal seam gas and open cut mining in the Surat Basin, Darling Downs, and Liverpool Plains, by several large companies has caused great interest in the community.
The proposed mining is open cut mining, conversion of low grade coal to liquid in a reactor, coal seam gas extraction and gassification on the site.
The Commonwealth Department of Sustainability and Environment has released of 300 conditions for 13 coal seam gas projects and a pipeline to Gladstone.
These conditions mainly address biodiversity and aquifer issues.
Two recently reported incidents of detection of benzene-related compounds near drilling sites from an unknown cause in SE Queensland.
Open cut mining requires large amounts of water for dust suppression.
Mining coal seam gas, both uses and releases from the seam a great deal of water, most probably very saline and unusable.
One proposed use of coal seam gas water is dust suppression and coal washing in a new coal mine.
Coal seam gas water is currently being used for dust suppression on roads in the region and coal washing.
The water that comes out of the coal seams may contain 5-8 tonnes of salt per megalitre to impact local prime farm soils.
Investigate what chemicals are in coal seam gas water and their effect on the growth of plants, not omitting the BTEX carcinogens benzene, toluene, ethylbenzene and xylene.
37.1.4 Oil shale and fracking, (hydraulic fracturing)
1. Hydraulic fracturing is the use of fluid under pressure to open deep shale rocks and release the methane trapped within them.
Oil shale is a fine-grained shale that yield oil when distilled.
Petroleum may be extracted directly from loose shales.
However, more petroleum can be extracted if the shale can be made looser artificially by a process called fracking.
Hydraulic fracking fluids can be injected under great pressure along with sand grains or other material to keep the shale particles apart when the hydraulic fluid is removed.
However, the hydraulic fluids pose a danger of environment pollution if they are forced by pressure to the surface.
Drinking wells near fracking sites have been contaminated with methane Some aquifers at similar depths those used in fracking sites have become contaminated with salt from salt aquifers nearby.
2. Oil drilling additives
Bentonite and barite | Calcium chloride | Sulfonated asphalt | Xanthan gum | Polyacrylamide (PAM) | Polyanionic cellulose (PAC) | Sodium carboxyethylcelulose (CMC) | Carboxymethyl starch sodium (CMS)
37.1.5 Fracking, by Josie Garthwaite, San Francisco (edited)
1. Fracking is used in nine out of every ten natural gas wells in the US.
2. Hydraulic fracturing involves cracking rock formations by pumping fluid into wells at high pressure, forcing oil or gas out of the rock.
It is also known as hydrofracking and fracking, and, most commonly, fracking.
Fracking can squeeze natural gas from layers of rock that would otherwise be too difficult or costly to exploit.
Drillers also use fracking to release gas from fine-grained sands, "tight sands", and to free methane from coal beds.
The pressurized fluid creates tiny cracks, or fissures, in the shale around a bore hole far below ground level.
Gas flows out of the rock and up to the surface.
The L shape wells, enabled by advances in “horizontal drilling” over the last decade, makes it possible to tap many small pockets of gas.
Horizontal drilling, combined with fracking, makes it worthwhile for companies to tap gas stores that would not have been economical.
3. Grains of sand, acting as “proppants” keep cracks in the shale open so gas can flow out of the rock and up the well.
Chemical “additives", help to dissolve minerals, reduce friction, prevent corrosion, thicken the fluid so it can transport the sand, and clean out debris.
Chemical ingredients may include hydrochloric acid, petroleum distillates, ammonium persulfate, calcium chloride, boric acid, citric acid, and borate salts.
Exposure to high amounts of some common frack fluid chemicals, e.g. ethylene glycol (antifreeze), have been linked to serious health problems.
4. Leaking well casings can allow gas to leak out of the well and into water aquifers.
Equipment failures and well blowouts can send wastewater flowing into nearby creeks.
From 30 to 70% of the original fluid volume does not come back out of the well right away, but remains "stranded" underground for years.
The wastewater that does bubble to the surface, which can now contain salts, minerals, and low level radioactive materials leached out of the soil and rock, must be recycled or disposed of.
Most frequently, this water is injected back into the earth, or is pumped to ill-equipped municipal sewage plants.
The EPA is now working on standards for shale gas wastewater treatment and disposal.
5. Re-injecting wastewater into fracking wells can also cause earthquakes that are "large enough to be felt and may cause damage".
37.1.6 Protecting the Great Barrier Reef
1. "The 27–year decline of coral cover on the Great Barrier Reef and its causes" [edited for this website] by Glenn De’atha, Katharina E. Fabriciusa, Hugh Sweatmana, and Marji Puotinenb, Australian Institute of Marine Science, Townsville, and School of Earth and Environmental Sciences, University of Wollongong.
Edited by Paul G. Falkowski, Rutgers, The State University of New Jersey, New Brunswick, NJ, May 25, 2012.
The world’s coral reefs are being degraded, and the need to reduce local pressures to offset the effects of increasing global pressures is now widely recognized.
This study investigates the spatial and temporal dynamics of coral cover, identifies the main drivers of coral mortality, and quantifies the rates of potential recovery of the Great Barrier Reef.
Based on the world’s most extensive time series data on reef condition, we show a major decline in coral cover from 28.0% to 13.8%, a loss of 50.7% of initial coral cover.
Tropical cyclones, coral predation by crown-of-thorns starfish, and coral bleaching accounted for 48%, 42%, and 10% of the respective estimated losses, amounting to 3.38% mortality rate.
Importantly, the relatively pristine northern region showed no overall decline.
The estimated rate of increase in coral cover in the absence of cyclones, crown-of-thorns starfish, and bleaching was 2.85%, demonstrating substantial capacity for recovery of reefs.
In the absence of crown-of-thorns starfish, coral cover would increase at 0.89%, despite ongoing losses due to cyclones and bleaching.
Reducing crown-of-thorns starfish populations, by improving water quality and developing alternative control measures, could prevent further coral decline and improve the Great Barrier Reef.
Water quality is a key environmental driver for the Great Barrier Reef.
Central and Southern rivers now carry up to ninefold higher nutrient and sediment loads from cleared, fertilized, and urbanized catchments into the Great Barrier Reef compared with pre-European settlement.
Global warming is also increasing rainfall variability, resulting in more frequent intense drought-breaking floods that carry particularly high nutrient and sediment loads.
River runoff of nutrients and sediments directly affects about 15% of reefs.
On these reefs, coral cover does not directly depend on water quality.
However, reefs exposed to poor water clarity and elevated nutrient concentrations show significant increases in macroalgal cover and reduced coral species richness and recruitment.
There is also strong evidence that water quality affects the frequency of crown-of-thorns starfish outbreaks in the central and southern Great Barrier Reef.
Survival of the plankton-feeding larvae of crown-of-thorns starfish is high in nutrient-enriched flood waters, whereas few larvae complete their development in seawater with low phytoplankton concentrations.
2. Local farmers are helping to reduce run off and improve water quality flowing into the Great Barrier Reef catchment.
In grazing lands, sediment loads are reduced by: setting stocking rates that maintain ground vegetation cover and biomass (particularly during droughts and at the end of the dry season) and vegetation diversity (including maintaining some tree cover particularly in riparian areas); and managing stock access to, and increasing ground cover in, riparian or frontage country and wetlands, and rilled, scalded and gullied areas.
Techniques for managing gully and stream bank erosion, which are known to be a significant source of sediments in grazing lands, are important and require further investigation as to their economic viability and effectiveness.
Soil management practices that reduce runoff and sediment movement reduce loads of particulate and total nutrients in runoff.
In most cropping systems of the Great Barrier Reef, management systems that reduce or eliminate tillage and maximize soil cover (via crop residue retention), and the use of grassed headlands, and where appropriate grassed inter-rows, reduce soil loss.
Controlled traffic and contour embankments also reduce runoff and soil loss.
Targeting practice improvement to areas contributing most to soil loss, considering erosion rates, soil texture and location of sediment traps, can increase the effectiveness at the Great Barrier Reef.
Losses of nitrogen are related to nitrogen fertilizer applications and nitrogen surplus (i.e. the difference between nitrogen inputs and nitrogen in crop off take) at the field scale and whole Great Barrier Reef.
Where surpluses are high, nutrient loads are most effectively reduced by reducing nutrient inputs and surpluses.
The same principles should apply to phosphorus.
When nitrogen applications closely match crop requirements (i.e. nitrogen surpluses are low), management ‘tactics’ such as splitting or altering the timing of fertilizer applications, altering fertilizer types and burying fertilizer, can help manage the risk of nitrogen supply limiting yield.
Nutrients from sources such as nitrogen from legumes and nitrogen and phosphorus from mill mud in sugarcane areas may substantially increase nutrient surpluses and thus have water quality impacts.
In furrow irrigated sugarcane, increasing irrigation efficiency (i.e. reducing over-application of irrigation) reduces nutrient losses.
Efficiencies can be increased either by better managing irrigation within a given system, or moving from systems with lower, (e.g. furrow), to higher (e.g. trickle), efficiency.
Soil management practices that reduce runoff and sediment movement (e.g. retention of crop residues, controlled traffic) reduce pesticide runoff.
Managing pesticide application timing (i.e. increasing the time between application and runoff) as well as the amount, placement and application method (e.g. banded spraying) will reduce pesticide runoff greatly, especially for the highly soluble photosystem II inhibiting herbicides.
Applying products with rapid degradation rates (e.g. ‘knockdown’ herbicides) will reduce concentrations and loads in runoff.
37.2.1 Cold air is heavier than warm air, inverted paper bag balance
See diagram 8.12: Balanced flasks.
1. Open two same size paper bags.
Attach identical pieces of string to the bottom of each bag with an identical pieces of adhesive tape.
Make a loop in the other end of each piece of string.
Put the loops over each end of a balanced rod.
Adjust the positions of the loops until the rod is horizontal.
Heat the air below one paper bag.
The end of the rod supporting that paper bag rises.
Leave the balance to stand without heating a bag.
The rod becomes horizontal again.
Heat the air below the other bag.
The other end of the rod rises.
This experiment shows that a volume of warm air weighs slightly less than a volume of cool air.
However, the experiment does not give any information about the weight of a volume of air.
The flame under the paper bag heats the air in it and it expands, following Charles's law.
Some heated air spills out of the paper bag leaving less air and less dense air in the paper bag.
The air in the heated paper bag weighs less than the air it displaces so by Archimedes' principle there is an upthrust greater than its weight that causes the paper bag to rise.
When you remove the flame, the warm air in the paper bag cools and contracts drawing in air at atmospheric pressure.
The weight of a paper bag full of air and the bag crunched together, with all the air squeezed out, is the same.
Air in a hot air balloon is heated, it expands and becomes lighter and the balloon is pushed up, because the air left in the balloon is less dense than the surrounding atmospheric air.
37.2.3 Convection box, smoke house
See diagram 37.13: Convection box.
Use an open box and cut a pane of glass so that it just covers the opening of the box to make a window.
Cut two holes in the roof of the box.
Place two lamp chimneys or plastic tubes over the holes.
Place a short piece of candle on the floor of the box under one chimney.
Light the candle.
This represents a land area that the sun has heated.
Close the window.
Trace the air current in each chimney with a smoking piece of piece of paper.
Observe the movement of smoke inside the box.
Move the candle so that it is under the other chimney and repeat the experiment.
The smoke moves, because of convection currents.
37.2.10 Layers of the atmosphere, lapse rate, auroras
See diagram 37.39.1: Atmosphere divided into vertical divisions.
1. Troposphere
The upper limit, the tropopause, varies from a height of 28 km in the tropics and 7 km in polar regions.
In this layer most of the components of weather occur including winds, water vapour, clouds, rainfall and lightning.
Temperature decreases with height, lapse rate (environmental lapse rate, ELR), by about 6.5oC (5oC to 10oC) per km.
The lapse rate depends on the amount of water vapour in the air.
Dry air cools at about 10oC / km, the "dry adiabatic lapse rate".
Moist air cools at > 6oC / km, the "moist adiabatic lapse rate".
Water vapour in rising air will condense when the air becomes cold enough.
The phase change from gas to liquid cause a release of latent heat of vaporization to be subtracted from the cooling effect.
So rising dry air cools faster than rising moist air.
Similarly, sinking dry air warms faster than sinking moist air.
Dry air cools much faster than humid air.
In a desert, day temperature are high, but have night temperatures may be low if no cloud cover.
In tropical climates with high humidity, but night temperatures are not far below day temperatures.
Moisture in the air prevents radiation cooling.
The dryer the air, the greater the diurnal temperature variation.
The latent heat of water keeps the moist air mass warmer than a dry air mass.
Dryer air (continental air mass) is much colder than humid air (maritime).
2. Stratosphere
The upper limit, the stratopause, is about 50 km, when the temperature ceases to rise.
The absorption of ultraviolet radiation from the sun in the stratosphere causes a rise in temperature resulting in it being a stable layer.
3. Mesosphere
In the lower part, the isothermal layer, the temperature hardly changes, then temperature decreases with height, down to -95oC, at about 80 km above the earth, the mesopause.
Above 80 km, charged particles from space, solar wind (electrons, protons and alpha particles), collide with atoms to cause excitement then emission of photons when oxygen and nitrogen atoms return to ground energy state, causing the phenomena of Aurora Borealis (Northern Lights) in the far north regions and Aurora Australis (Southern Lights) in the far south regions.
Nitrogen atoms emit red light and oxygen atoms emit green light.
4. Thermosphere
This layer of rising temperature above the mesopause may extend for 400 to 500 km depending on the activity of the sun.
Ultraviolet rays and X-rays from the sun break molecules into atoms and ions.
5. Exosphere
This level contains a very low density of neutral atoms and molecules, and electrically charged particles.
This level merges with the interplanetary region.
6. Ionosphere (the upper mesosphere and the thermosphere)
This region of concentration of ions, the ionosphere, acts as a reflector of radio waves, sky waves.
Reflection properties change with height, from 50 to 150 km level, and change diurnally and with different solar activity.
Television waves are have shorter wavelengths than longer wavelength radio waves and are not reflected by the ionosphere.
The wavelengths used by satellites must be shorter than radio waves so that they can penetrate the ionosphere.
37.2.9 Inversion layers
Most of the atmosphere, and nearly all of the water vapour, is contained in the troposphere, a layer up to 20 km deep in the tropics and 8 km deep at the poles.
Weather occurs in the troposphere.
Between the troposphere and the stratosphere is the tropopause where the temperature no longer decreases with altitude, but starts to increase.
The temperature, density and pressure of the atmosphere decreases with height.
The drop in temperature, the lapse rate, is about 6.5oC per km increase of height.
During the day, radiation from the sun heats the ground much faster than it heats the air.
The ground then heats the air in direct contact with it and this warm air rises.
As the volumes of ground-heated air rise, they expand to match the lower density of the air around them, like a hot air balloon.
Expansion of an air volume causes it to cool at about 10oC per km height.
However, this rising volume of air may remain warmer than the air surrounding it.
So it can continue to rise, causing unstable turbulent conditions when the warmer and cooler air mix.
On dry cloudless nights, the ground cools faster than the air due to radiation of heat out to space.
The ground cools the air in contact with it so the temperature of the atmosphere increases with height to produce a temperature inversion.
It traps pollutants in this lower layer, e.g. smoke from fires and exhaust gases from motor cars.
The boundary where the switch of temperature change occurs can be clearly seen from above the inversion layer, like a hill.
In the morning, the sun heats the ground.
The ground then heats the air in direct contact with it and this warm air rises.
Unstable conditions begin, the inversion layer is broken, and the usual cycle starts again.
37.2.9a Inversion layers
Experiment
Use a transparent square tank with an immersion heater at the bottom.
Fill the tank half full of cold water.
Carefully pour hot water on top to form a separate layer.
Shine a strong torch through the water onto a screen.
Note the sharp boundary, because of the difference in refractive index of the water at different temperatures if no mixing between the two layers occurs.
Turn on the heater at the bottom of the tank.
Note the warm water rising through the cold layer as a turbulent swirling shadow on the screen.
When the rising water reaches the hot water layer, it rises no further and is trapped.
In the atmosphere, the inversion layer prevents mixing between the troposphere and higher atmosphere.
Water does not move through and no clouds occur beyond the stratosphere, otherwise the Earth would eventually lose all its water.
Material that does get into the stratosphere layer stays there for years and can take part in chemical reactions, e.g. reactions with ozone and oxygen atoms.
Radiation at around 265 nm is most dangerous to living things, including plants.
Ozone prevents radiation below 290 nm from reaching the ground.
Ozone also stops great deal of radiation in the 290 nm to 320 nm range.
This radiation causes skin cancer.
Concentrations of ozone in the stratosphere fluctuate with natural changes in rates of production and destruction.
In any one year, the maximum concentrations in the spring can be half as high again as the minimum in the autumn.
While the rates of ozone production appear to be out of control, the compounds added to the atmosphere will affect the destruction.
The oxides of nitrogen, both natural and from car pollution, account for perhaps two thirds of the destruction.
37.2.5 Trade winds and weather rotations
1. The circumference of the Earth at the equator is larger than near the north pole or south pole and the Earth rotates once every 24 hours, so the surface of the Earth at the equator must move faster at the equator than near the north pole or south pole.
A super missile fired from the north pole and aimed at the south pole would to be deflected to the right in the Northern Hemisphere and deflected to the left in the Southern Hemisphere.
The Coriolis force does not only operate on objects travelling in a north south direction.
The size of the Coriolis force is independent of the direction in which something is moving.
The missile goes similarly off track after being fired in an easterly or westerly direction.
Some people regard "Coriolis force" as a fictional force used to account for movement of air and water over the spinning Earth and "Coriolis acceleration" refers to the apparent tendency of a moving body to swing to one side when its motion is defined by rotating axes.
Other people do not use the term "Coriolis effect", because it is too vague.
They say that in a rotating co-ordinate system there is a Coriolis force that causes a mass to be accelerated.
The Coriolis force does no work, but that does not disqualify from being called a force.
2. The rotation of the Earth does influence the direction of rotation of large weather systems and large vortices in the oceans.
These long-lived phenomena allow the very weak Coriolis force to produce a significant effect, given enough time.
The Coriolis force causes the air to rotate around a low pressure centre in a cyclonic direction, i.e. air or water rotates in the same direction as the Earth.
The air flowing around a cyclone (hurricane, typhoon) spins anticlockwise in the Northern Hemisphere, and clockwise in the Southern Hemisphere.
If the Earth did not rotate, the air would flow directly in towards the low pressure centre.
3. The Coriolis force, operating on its own causes a moving object to experience a force to the right of its path in the Northern Hemisphere and to the left of its path in the Southern Hemisphere.
In a geophysical flow in the atmosphere or oceans, there is always another force operating, e.g. the pressure gradient force that cause material to start to move.
The direction of any rotation depends upon the net force where the Coriolis force and other forces are present.
Around a high atmospheric pressure area, the pressure gradient force points radially outward.
Around a low atmospheric pressure area, the pressure gradient force points radially inward.
4. If a body of air moves horizontally at constant speed where friction with uneven terrain is negligible, the two horizontal forces on it are the pressure gradient force and the Coriolis force.
If the magnitudes of these forces are equal then the Coriolis force does not cause a deflection to left or right.
The Coriolis force may be larger or smaller than the pressure gradient force, depending on the wind speed.
If the pressure gradient force is greater than the Coriolis force, the flow will be curved around a low pressure area.
In the Northern Hemisphere the flow of the gradient wind is anticlockwise around the low pressure areas, because the Coriolis force acts to the right.
In the Southern Hemisphere the flow of the gradient wind is clockwise around the low pressure areas, because the Coriolis force acts to the left.
37.2.5a Trade winds and weather rotations
Experiment
Study the direction of rotation winds around Highs and Lows from weather charts in the newspaper or on television.
It is unlikely that the construction of wind farms affects the rotation of the earth.
The relative forces are not comparable.
Some people have suggested that half the wind farms could face east and the other half face west to counteract any effect on the rotation of the earth!
37.2.14 Trade winds, easterlies and westerlies
A wind in the Southern Hemisphere, originally heading due North towards the equator, will reach the equator to the west of its original point of aim.
At the equator, an observer will observe more easterly winds called the trade winds that blow from the southeast in the Southern Hemisphere and from the northeast in the Northern Hemisphere.
Trade winds from north and south meet near the equator so the air rises, cools and forms rain to create tropical conditions.
Similarly a wind heading towards the South Pole from the equator will arrive east of the original point of aim, to produce westerlies across the middle latitudes, e.g. the roaring forties that blast around the Southern Hemisphere at 40o to 50o latitude.
Both trade winds and westerlies blow away from 30o latitude region.
37.2.4 Direction of water through a bath plug hole.
Coriolis effect (Coriolis force)
Some people think that when water goes down a bath plug hole its direction of spin is determined by the Coriolis effect.
These people say that if you leave the water still in the bath for a long time then pull out the plug it will spin anticlockwise in USA and spin clockwise in Australia.
Other people say that the Coriolis effect is too small to affect the small amount of water in a bath tub and they cannot produce the effect by experiment in a bath.
The Coriolis force is very small compared with common rotations, e.g. water down a plug hole, because the rotation of the Earth is only one rotation per day.
The direction of rotation of water down a plug hole depends on the way it was filled or by vortices due to washing action.
Experiment
To obtain the rotation down a plug hole that is always cyclonic, use a 1m smooth pan with a very small hole in the centre and a stopper that can be removed from below.
Leave the water undisturbed for weeks before removing the stopper so that the water takes hours to drains through the hole.
As a fluid parcel moves towards a wall it will be deflected and turn.
It is this rotary motion that is accentuated when the water converges towards the drain.
Similarly, some people report that if you put a flat round dish full of still water in a refrigerator, the water heaps up as it freezes to form a roughly north-south ridge, because of the Coriolis force.
37.2.16 Weather maps (synoptic charts), Buys Ballots law, geostrophic wind and gradient wind
See diagram 37.149.1: Geostrophic wind flow.
See diagram 37.149.2: Gradient wind flow.
See diagram 37.149.3: Veering and backing wind.
1. Study laminar and turbulent flow from weather maps.
Daily weather maps show large scale fluid dynamics.
The usual weather map is a mean sea level synoptic chart.
Synoptic means overall view.
Lines on a weather map joining places of equal atmospheric pressure are called isobars.
An anticyclone may be shown by a group of isobars labelled high or H and the central pressure in hectopascals.
Anticyclones, highs, are much larger than lows, cyclones, so the pressure gradients of highs is more gradual and so generate lighter winds than lows.
Anticyclones that do not move for long periods, blocking highs, cause the weather pattern to remain constant.
The winds blowing from the centre of highs towards lows blow anticlockwise around the high in the Southern Hemisphere and clockwise in the Northern Hemisphere under the influence of the Coriolis effect.
2. Buys Ballot, 1817-1890, Netherlands, a Dutch meteorologist, described the relationship between wind direction and pressure as shown by isobars.
The Buys Ballots law states that if an observer stands with the back to the wind, in the Northern Hemisphere the lower pressure is to the observer's left and in the Southern Hemisphere the lower pressure is to the observer's right.
So if an observer standing in the Southern Hemisphere feels the wind blowing into the face, the pressure on the observer's right is higher and on the observer's left is lower.
If an observer facing south feels a southerly on the face then feels a wind on the right side of the face, the wind has veered from a southerly wind to an easterly wind.
If the wind then moves back to a southerly wind, the wind has backed.
So the direction of a veering wind moves clockwise, to the right, and the direction of a backing wind moves anticlockwise, to the left.
3. An air mass moving horizontally at constant speed with no friction with the surroundings has two forces on it:
* the pressure gradient force from high pressure to low pressure, and
* the Coriolis force.
If the two forces are exactly equal and opposite, the air mass continues moving as a geostrophic flow horizontally in a great circle around the world, i.e. in a straight line on a synoptic weather chart.
For any given latitude, at a certain wind speed, called the geostrophic speed 2.1 = (b).
As no Coriolis force exists at the equator, air masses there move in the direction of the pressure gradient force from high pressure to low pressure.
Similarly, no geostrophic flow occurs between 15o north and 15o south, because the Coriolis force is too weak.
4. If 2.1 is not equal to (b), the air mass moves to the left or right tangential to the isobar as a gradient wind, i.e. along the curved isobars on a synoptic weather chart.
If the pressure gradient force is greater than the Coriolis force, the air mass moves in a curve around a low pressure area, anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
This curved motion is called cyclonic flow and is in the direction of the Earth's rotation.
Remember that an observer above the north pole would observe the Earth spinning anticlockwise and an observer below the south pole would observe the Earth spinning clockwise.
Regions of high pressure, anticyclones are found mainly over the poles and around the globe at 30o of latitude each side of the equator.
Regions of low pressure, troughs, are found mainly near the equator and between 30o of latitude and the poles.
If the pressure gradient force is less than the Coriolis force, then the movements of the air mass is the opposite to the movements as in 3.
5. Measure surface wind at a standard level of 10 m above the Earth's surface where forces of friction with the rough surface of the Earth decrease the geostrophic wind speed and cause the wind to move across the isobars at an angle of about 30o over land and 10o over sea.
At about 1 km above the ground the friction force is zero.
6. Horizontal convergence refers to a gain of air mass above a place causing increased atmospheric pressure.
Horizontal divergence refers to a loss of air mass above a place causing decreased atmospheric pressure.
Low pressure at X causes air to move towards X due to the pressure gradient force, followed by slow upward movement of air.
If the upward moving air contains moisture, cloud will form at X1.
Low pressure areas are associated with a low, low pressure centre, depression or cyclone and wet weather.
A trough is an elongated area of low pressure.
High pressure at Y causes air to move away from Y, followed by a slow downward movement of air.
So clouds do not form at Y1. High pressure areas are associated with a high or anticyclone and fine weather with light winds.
A ridge is an elongated area of high pressure.
Horizontal winds, advection winds, are always much greater than vertical winds, convection winds.
37.2.2 Composition of the atmosphere and greenhouse gases
Gas and percentage volume in dry air:
N2 78.08%, O2 20.95%, Ar 0.93%, CO2 0.03%, Ne 0.0018%, He 0.00052%, Kr 0.00011%, Xe 0.000009%, Rn 6 × 10-18%.
The average molecular mass of air molecules is 28.8 (80% of 28 + 20% of 32).
The apparent molar mass is 28.96 g / mol.
The main greenhouse gases are as follows:
1. water vapour from evaporation of water or sublimation of ice,
2. carbon dioxide, an acidic oxide, from burning of fossil fuels, wood and chemical reactions.
However, plants remove carbon dioxide from the atmosphere, sequester, during photosynthesis so concentration drops during the Northern Hemisphere growing season.
Carbon dioxide transmits visible light, but absorbs infrared radiation.
3. Methane, CH4, from volcanoes, coal, natural gas, oil, digestion by herbivores and anaerobic decay of plants in rice paddy and solid waste landfills.
4. Nitrous oxide, N2O from combustion of fossil fuels and solid wastes and from chemical reactions and agricultural activities including emission by tropical soils.
5. Ozone, O3, concentrated in the ozone layer of the atmosphere, shields the earth from excess high frequency ultraviolet light.
However, it harms the respiratory system.
An ozonesonde is an instrument on a balloon, linked to meteorology radiosonde, that up to 35 km measures ozone, height, pressure, temperature and humidity.
6. Chlorofluorocarbons, CFCs, contain C, Cl and C, e.g. perfluorocarbons, e.g. tetrafluoromethane (CF4, carbon tetrafluoride, R14)
7. Hydrofluorocarbons, HCFCs, contain C, Cl and C, and also contain H, e.g. tetrafluoroethane (CH2FCF3, R-134a)
Examples:
Halon-1211, bromochlorodifluoromethane (CBrClF2), RODP
Halon-1301, bromotrifluoromethane (CBrF3), RODP
Freons, CFCs, chlorofluorocarbons, "Freons"
8. Sulfur hexafluoride (SF6), a very dense gas, has the most potent global warming potential (GWP) and is released by industries, but is not ozone-depleting as are CFCs, e.g. dichlorodifluoromethane (CCl2F2, R-12, "Freon-12").
37.2.6 Greenhouse effect in a model greenhouse
A blanket on a bed reduces heat loss by reducing conduction.
Air, a poor conductor of heat is trapped within the threads of the blanket, and between the blanket and the person on the bed.
Similarly, the glass roof of a greenhouse or cucumber frame traps air and so reduces heat loss by conduction and by convection.
However, the greenhouse effect also reduces heat loss by radiation.
The sun emits light and short wavelength infrared radiation that can pass through gases in the atmosphere and the glass roof of a greenhouse to heat the Earth and the contents of the greenhouse, that in turn emit longer wavelength infrared radiation as their temperature rises.
Some longer wavelength radiation emitted by the Earth is absorbed by "greenhouse gases" in the atmosphere that have three or more atoms in each molecule, e.g. carbon dioxide, methane, nitrogen oxides, ozone and water vapour, which in turn emit about half of this radiation to be absorbed by the lower atmosphere and the Earth to give an average temperature of +18oC instead of -18oC if the greenhouse gases did not exist.
However, the longer wavelength radiation cannot pass through glass, so the contents of the greenhouse get hotter than if outside the greenhouse.
If you place a sheet of glass between a red hot fire and your hand, you cannot feel any heat from this longer length radiation.
So the "greenhouse effect" is a natural process accentuated in the last two hundred years by industrial and agricultural development causing increases in the concentration of "greenhouse gases" in the atmosphere.
This increase has probably caused "global warming" the steady increase in average temperature now being experienced.
Some people say that "greenhouse effect" is a misnomer, because the main function of a greenhouse is to stop loss of heat by convection, yet allow plants to receive the radiation necessary for photosynthesis.
If that is true, then the above experiment is not a good simulation of the greenhouse effect.
A plant greenhouse traps insolation.
The glass roof and sides transmits most radiation wavelengths, except the infra-red and ultraviolet wavelengths.
The radiation that passes through the glass is absorbed by the plants, which then get warmer and radiate infra-red radiation that cannot pass through the glass.
So a greenhouse is a "hot house".
37.2.6a Greenhouse effect in a model greenhouse
Experiments
1. Use a thermometer to read the ambient temperature in the shade.
Leave a closed bottle in direct sunlight for some time.
Put the bottle in the shade, open it and read the inside temperature with the thermometer.
2. Hold a sheet of glass between your hand and the sun.
You can feel the increase in temperature due to the radiant heat passing through the glass.
Hold the sheet of glass between a fire and your hand.
You cannot feel any temperature change due to the radiant heat from the fire passing through the glass.
3. Line a household bowl with aluminium foil.
Put a piece of food, e.g. cheese, on the end of a tooth pick and fix it in the centre of the bowl.
Cover the bowl with clear food wrap and leave the bowl in the sun.
The bowl acts as a greenhouse and the cheese melts.
4. Use two small identical packets or cardboard boxes.
Cut identical square holes in the upper surface of each box.
Punch a hole in the side of each box and insert a thermometer through the hole.
Find a piece of window glass to cover the square hoe of one box or make a glass roof with microscope slides.
The other box has no cover over the square hole in the roof.
The initial readings of the two thermometers should be the same.
Take the boxes out of the room and put them in the direct sunlight for 20 minutes.
Read the thermometers and record the temperature.
The box with the glass covering the square hole is a model greenhouse.
It absorbs radiant energy though the glass roof.
The temperature in the model greenhouse box is greater than the temperature in the other box.
The sun emits light and short wavelength infrared radiation that can pass through gases in the atmosphere and the glass roof of a greenhouse to heat the Earth and the contents of the greenhouse that in turn emit longer wavelength infrared radiation as their temperature rises.
Some longer wavelength radiation emitted by the Earth is absorbed by gases in the atmosphere, e.g. carbon dioxide, methane and water vapour, which in turn emit some of this radiation to be absorbed by the Earth.
However, the longer wavelength radiation cannot pass through glass, so the contents of the greenhouse get hotter than if outside the greenhouse.
37.1.3 Global warming and climate change
1. It is estimated that while the average sea level has risen 222 mm since 1875, i.e. 1.7 mm per year, during the period 1993 to 2009 it rose 3 mm per year.
This much faster increase was possibly caused by increased average annual temperatures leading to expansion of seawater 30%, ice melting in glaciers and ice sheets in Greenland and Antarctica, 55%, and increased wetlands drainage, 15%.
This evidence of global warming may be called the enhanced greenhouse effect.
The problem is how to distinguish this global warming from patterns of climate change in the past that included long periods of warming and cooling, e.g. the ice ages.
2. Climate change "warmists" refer to people who believe that climate is warming, because of human activity and the increased concentration of carbon dioxide in the air.
Here is a 2005 definition of (global) warmists:
"To be defined as a global warmist, a person must have all of the following traits:
* An absolute belief that humans are primarily or even completely responsible for causing a mass climate change which will raise the average temperature of the planet.
* Will not entertain the idea that it is possible that natural phenomena may cause climate change, regardless of any evidence.
* Believes it is a good thing to throw billions upon billions of dollars at an idea that may or may not work to stop climate change, just in case.
* Believes that natural disasters such as hurricanes and earthquakes are an indirect result of humankind's actions to cause climate change.
* Shouts down, puts down, and insults anyone whose beliefs run contrary to their own, rather than having intelligent discourse."
3. Climate science "deniers" claim that climate science is a “leftist fad” and a “work of fiction”.
They request authorities to “remove environmental propaganda material, in particular 'post-normal science' about 'climate change’, from the school curriculum.
They assert the existence of "reams of scientific papers over many decades that have attempted, but failed to falsify the “theory” that burning fossil fuels is causing the world’s average temperature to rise, the oceans to become more acidic, the sea levels to rise and the ice at the poles to melt.
"While consistently claiming that school children are being brainwashed by climate change “propoganda”, those who push this line rarely (if ever) produce any actual evidence."
In Australia, a survey of political representatives at local, state and federal level done in late 2009 found that acceptance of climate change science was divided along political lines.
Sydney radio host Alan Jones, recently told a crowd that climate science was “witchcraft” and a ”hoax”.
37.2.13 Storm glass
The "storm glass" is a solution of salts that changes to form different types of crystals in different weather conditions, probably caused by changes in temperature.
The liquid within the sealed glass container contains ethanol, potassium nitrate, ammonium chloride and camphor.
It was invented by Captain Robert Fitzroy, founder of the UK Meteorological Office and formerly the captain of HMS Beagle.
From Australian Geographic:
During Charles Darwin's historic voyage in the Beagle, 27-12-1831 to 2-10-1836, Captain FitzRoy carefully documented how the storm glass would predict the weather:
If the liquid in the glass is clear, the weather will be bright and clear.
If the liquid is cloudy, the weather will be cloudy as well, perhaps with precipitation.
If there are small dots in the liquid, humid or foggy weather can be expected.
A cloudy glass with small stars indicates thunderstorms.
If the liquid contains small stars on sunny winter days, then snow is coming.
If there are large flakes throughout the liquid, it will be overcast in temperate seasons or snowy in the winter.
If there are crystals at the bottom, this indicates frost.
If there are threads near the top, it will be windy.
In 1859, violent storms struck the British Isles.
In response, the British Crown distributed storm glasses, then known as "FitzRoy's storm barometers," to many small fishing communities around the British Isles that were to be consulted by ships at port before setting sail.
37.2.12 Ocean Iron Fertilization (OIF)
An unproved theory that iron is a limiting nutrient in oceans and the supplementary application of iron would beneficially stimulate phytoplankton populations to act as a biological carbon pump to sequester carbon dioxide.
37.2.11 Navigation data used by a ship at sea
Position: 10.23 UTC (Co-ordinated Universal Time (UTC) replaced Greenwich Mean Time (GMT) as the World standard for time in 1986.
It is based on atomic measurements rather than the earth's rotation.
Greenwich Mean Time (GMT) is still the standard time zone for the Prime Meridian (Zero Longitude).
20o57.05' S
039o52.82' W
Course: 32o
Speed: 18.8 Kts (knots)
Relative wind: 55 Km \ h
Depth of sea: 47 metres (154 feet)
N NE E
Ships time: 07.29
Water temperature: 25oC
Air temperature: 29oC
Conditions: Cloudy sky
Air pressure hPa
Beaufort Wind Scale 3 (Beaufort number 0 --> 12)
Wind direction: 8 km / h from south
Barometer: 1015 mb, 761 mm Hg, 30.00 inch
Tendency: Slowly increasing
37.2.20 Weather sayings
1. "Clear moon, frost soon"
With no clouds to impede heat lost by radiation the earth cools quicker and frost is more likely.
2. "Rainbow in the morning gives a fair warning"
Rainbows appear in the side of the sky opposite the sun so a rainbow in the western sky indicates rain as the system moves from west to east.
3. "Red sky at night, shepherd's delight, red sky in morning, shepherd's warning"
1. Weather systems usually move from west to east.
Dust and moisture in the air makes the sky red towards sundown.
High concentration of particles in the air means that the atmosphere is stable, air pressure is high and weather next day will be fine.
However, in the morning, high concentration of particles in the air may indicate that a storm cell is approaching.
2. Over most of Europe weather systems usually come from the west, hence the saying:
"A red sky in the morning gives a shepherd warning.
A red sky at night gives a shepherd delight."
Similarly, in the Bible, Matthew 16: 3 (King James version): "And in the morning, It will be foul weather today: for the sky is red and lowering.
O ye hypocrites, ye can discern the face of the sky; but can ye not discern the signs of the times?"
4. "Ring around the moon, rain or snow soon"
The ring is caused by the ice crystals in cirrus clouds that indicates that low pressure is approaching, associated with a warm front.
The brighter the ring the more likely the incidence of rain or snow.
A similar ring may form around the sun.
5. "Year of snow, year of plenty"
More stable cold weather during winter is better for crop plants that a mixture of warmer and cooler weather that may cause "false springs" and the untimely flowering of plants.
37.2.8 Hot air rising
When air is heated, it expands as the air particles move faster, and consequently the air becomes less dense.
However, the heated air will not rise by itself.
Cooler air around it is less dense, weighs more, and squeezes the lighter less dense air up.
So the rising of the hot air is caused by the falling of the cooler air.
The rising is controlled by gravity.
The heated air does not rise by itself, but rises because it is pushed up!
37.48 Dew point
Wet and dry bulb thermometer, hygrometer, "Scientrific" (commercial website).
The atmosphere usually contains some water vapour, but less than required for saturation or partial saturation.
Saturation vapour pressure decreases as the temperature decreases, so the amount of water vapour required for saturation decreases as the temperature lowers.
If the temperature of the air is lower, the mass of water vapour in the air does not change.
A temperature will be reached where the mass of water vapour in the air is sufficient to saturate the air at this lower temperature.
At this temperature moisture is deposited and that temperature is the dew point.
The dew point is the atmospheric temperature at which dew is deposited, depending on pressure and humidity, i.e. at which the pressure of atmospheric water vapour becomes equal to the saturation vapour pressure.
So relative humidity = saturation vapour pressure at the dew point / saturation vapour pressure at the room temperature.
For every 1oC difference in the dew point and dry bulb temperatures, the relative humidity decreases by 5%, starting with relative humidity = 100% when the dew point equals the dry bulb temperature.
The dew point is the temperature to which a given parcel of humid air must be cooled, at constant barometric pressure, for water vapour to condense into liquid water.
The condensed water is called dew when it forms on a solid surface.
The dew point is a saturation temperature.
The dew point is associated with relative humidity.
A high relative humidity indicates that the dew point is closer to the current air temperature.
Relative humidity of 100% indicates the dew point is equal to the current temperature and the air is saturated with water.
When the dew point remains constant and temperature increases, relative humidity will decrease.
The dew point is derived from dry bulb and wet bulb temperatures, with a correction for elevation above sea level.
Relative humidity = mass of water vapour in a given volume of the atmosphere / mass of water vapour required to saturate the same volume at that temperature.
Relative humidity = vapour pressure of the water vapour in the air / saturation vapour pressure at the same temperature × 100%
Relative humidity = saturation vapour pressure at the dew point / saturation vapour pressure at room temperature
If the dry bulb temperature is the same as the dew point, the air is said to be saturated and the relative humidity is 100 %.
Relative humidity is also approximately the ratio of the actual to the saturation vapour pressure.
Actual vapour pressure is a measurement of the amount of water vapour in a volume of air and increases as the amount of water vapour increases.
Air that attains its saturation vapour pressure has established an equilibrium with a flat surface of water.
So an equal number of water molecules are evaporating from the surface of the water into the air as are condensing from the air back into the water.
37.2.7 Height values, sea level
The two reference surfaces commonly used as a basis for height values are the sea level surface (or geoid) and the spheroid.
In a ‘flat earth’ model, the two surfaces are considered coincident, but in a ‘curved earth’ model, this is rarely the case.
In most parts of the world, distance above sea level has been the traditional mechanism for measuring height.
This has been caused by:
* a preference for a physically identifiable surface as a reference,
* the importance of sea level to economic activity, e.g. shipping.
* the linkage between sea level, the earth's gravity field, and the conventional instrumentation used to measure height differences,
* the importance of gravity-related heights to water flow problems.
The Australian Height Datum (AHD) is an example of this last system.
37.2.15 Warm fronts and cold fronts
An air mass is a huge mass of air with its own property of temperature and humidity gained from the original land or water below it, e.g. tropical, equatorial and arctic air masses.
The air masses keep moving with cold air masses moving towards the equator and warm air masses moving towards the poles.
Where air masses with different properties meet is called a front.
A faster moving colder air mass pushing under a warmer air mass produces a cold front.
The warmer air is pushed up and its water vapour condenses to quickly form clouds and rain.
A warmer air mass passing over a colder air mass produces a warm front with light longer period rain.
Warm fronts and cold fronts
37.38.2 Cold front
37.38.4 Hurricane, tropical cyclone, typhoon
37.38.3 Tornadoes
37.38.1 Warm front
37.38.1 Warm front
Warm fronts are preceded by a slowly falling barometer.
Cirrus clouds will be observed and precipitation can usually be expected in 24 to 36 hours.
The cloud pattern gradually thickens as it progresses from cirrus to cirrostratus, then altocumulus or altostratus, and finally to nimbostratus or cumulonimbus.
Precipitation often begins from dense altostratus clouds before being obscured by the lower stratus or cumulus types of clouds.
As the front passes the wind changes direction, the barometer rises a little, precipitation ends, the sky begins to clear, and the temperature begins to rise noticeably.
In summer, afternoon thundershowers may develop behind a warm front.
37.38.2 Cold front
When a cold front approaches the barometer falls rapidly.
Cold fronts move faster than warm fronts, having an average speed of 32 to 40 km per hour, although they sometimes move at less than 16 km per hour and occasionally at more than 56 km per hour.
The procession of cloud types will be proportionately faster than those associated with a warm front.
The transition from cirrus to cirrostratus and then to altostratus or altocumulus of ten takes place within a period of a few hours.
Precipitation may start from 12 to 30 hours after the cirrus is first seen.
In the summer, cumulus clouds will build into cumulonimbus and produce thundershowers.
In winter, nimbostratus or stratocumulus will bring rain or snow.
When the front passes the wind will shift abruptly, the barometer will rise steadily, and the temperature will fall.
If the front is moving rapidly, clearing will begin quickly, but if the front is comparatively slow moving, cloudiness and some precipitation may last for several hours.
.
 Altitude Altitude Altitude
.
 Polar climate Temperate climate Tropical climate
Upper level 3 to 8 km 5 to 13 km 6 to 18 km
Middle level 2 to 4 km 2 to 7 km 2 to 8 km
Lower level Ground level
to 2 km		 Ground level
to 2 km		 Ground level
to 2 km

37.38.3 Tornadoes
Tornado or waterspout has a characteristic funnel cloud is caused by violent, vertical funnel-shaped vortex hanging from a cumulonimbus cloud base.
It may reach the surface.
Violent winds near the axis may do great damage along a narrow track.
In Australia a small local tornado is called a dust devil or willy-willy.
Tornadoes are created by the same atmospheric conditions that cause hail and thunderstorms, a collision of warm moist air and cold dry air masses.
If different wind speeds occur at different altitudes, a horizontal spinning column of air, a vortex, may form.
If the vortex collides with a violent updraft, it may be knocked into a vertical position, which on reaching the ground causes a tornado.
The tornado is usually cone-shaped, because the higher pressure near the ground squeezes the bottom of the vortex.
At very low pressure, water vapour in the air condenses to produce a funnel-shaped cloud.
Tornadoes cannot be predicted, but the air conditions that breed them are not completely understood.
Covering an area from 70 to 330 metres in width, a tornado usually travels with an average speed of 32 to 63 km per hour, although the wind velocity may be 300 km per hour.
In the Northern Hemisphere, tornadoes most frequently occur between 1 April and 15 July, and generally in the late afternoon.
A tornado is possible whenever the air is humid, with temperature above 26oC, and a cold air mass arrives.
Mammatocumulus clouds, like smooth globular udders, may extend down from different cloud types and are often seen under cumulonimbus clouds before and after a tornado.
The first sign of a developing tornado or waterspout in a tuba, a column of cloud in the centre of a vortex extending down from cumulonimbus cloud.
It may touch the ground.
37.38.4 Hurricane, tropical cyclone, typhoon
The tropical hurricane is the most devastating of storms.
Though occurring all over the world, but under different names, all hurricanes originate in the equatorial regions.
North of the equator their usual travel direction is north to north-west to north-east.
However, south of the equator hurricanes travel in the opposite direction.
Hurricane, cloud formations are similar to a warm front with the usual sequence of changes as follows:
1. cirrus,
2. cirrostratus about 1, 600 km in advance of the hurricane,
3. altostratus,
4. nimbostratus rain clouds or cumulonimbus.
A halo is often seen about the sun or moon.
Although a hurricane travels only 12 to 24 km per hour, it is accompanied by winds that may reach 240 km an hour.
In its life of about ten days, a hurricane covers an area of 800 to 3, 200 km2.
When the barometer begins to rise and the winds change direction, the worst of the hurricane is over.
The "eye of the storm" is an area of still air in the centre of a tropical cyclone, where air is descending instead of rising rapidly and the sky may be clear.
The winds each side of the "eye" blow in opposite directions.
37.2.17 Weather pictures
Experiment
Immerse a piece of white absorbent paper in a solution containing two parts cobalt chloride to one part common salt.
While wet, the paper will remain pink, but when dried in the sun or near a Bunsen burner it turns blue.
This is the basis of the weather pictures.
A home-made picture can be made in the following way.
Obtain a picture in which there is some sky or water and make an inset of the prepared absorbent paper to replace the sea or the sky.
The picture should then be mounted on a card and hung near a window where it will quickly respond to changes in the hygrometric state of the atmosphere.
37.2.18 Weather periods
Alexander Buchan (1829-1907, Scotland), used the average of many weather observations to determine six cold and two warm periods, the latter being 12-15 July and 12-15 August.
Since his work, climatologists have determined different patterns of weather periods in different places.
37.2.19 Weather records
See diagram 37.137: Wind direction record.
Experiment
Record the date, hour, temperature, sky and wind in a table.
Take readings at the same time each day, e.g. 9.00 am and 3.00 p.m.
Make entries in a notebook under the following headings:
Table 37.31
Date Time Temperature Sky Wind Rain
Draw graphs of temperature / time, rainfall / time, change in appearance of the sky over a period of time and changes in wind intensity.
Record the velocity of the wind as follows:
Table 37.31a
Light wind moves smoke, but not wind vanes
Moderate wind raises dust and just moves twigs
Strong wind large branches move
High wind blows dust, papers and moves whole trees.
Gale breaks off twigs from trees.
Experiment
Show the direction of the wind by an arrow in the wind column of your records or construct a paper star and draw a line each day along the arm that most nearly coincides with the direction of the wind.