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Climatology A Introduction this unit initiates the terrestrial environment 1 Weather refers to the daytoday variations and shortterm predictions about N L 4 V39 O l 00 O Thus it is actually a misuse by rainfall and temperature Climate refers to the average pattern of environmental conditions expressed as annual or and monthly averages of rainfall and temperature measured in air environment 39 to use for 39 39 conditions in very small places better to say microenvironment Smiths discuss microclimates Pgs 3440 Climatic variations have a greater effect on terrestrial environments because of the low speci c heat of air and land as compared to aquatic environments so temperature variations are much greater Also since the atmosphere can hold only a limited amount of water at saturation the amount of rainfall is highly variable especially over land Climates strongly affect the vegetation structure Recall von Humboldt the wealthy benefactor of science who traveled and financed scientific investigations on relation between temperature rainfall and the vegetation Recall that Grisebach in recognition of the effect of climates on the vegetation distinguished formations as structural type of vegetation that re ected the type of climate Recall V E Shelford renamed the formations of Botany biomes because he included the whole community the biocoenosis the animals and microbes as well as the plants Climatologists have always used this relationship with biological communities the formations or biomes as a guide for distinguishing and classifying climates Recall that the physical part of the ecosystem is the biotope which term Hesse so used in his Ecological Animal Geography Therefore the climate is an important part of the biotope B Local Climates l N L This is data gathered at a weather station and synthesized to show a local climate of a small area in the human perspect1ve Local data is important especially for ecologists as weather often shows great variations over small geographical areas as between different places as in Brazos County where TAMU is where it may rain heavily and at the same time nearby not at all The syntheses of many local climates are used to make the generalizations that we call climates C Representation of Climates l Climagraphs This method has been much favored by American ecologists pg 213 in Smiths a Plot monthly average temperatures against average precipitation by months b This yields a polygon that is supposedly a figure illustrating the overall climate c However the seasonal patterns are poorly visualized 2 Climate charts or diagrams These are used by climatologists and European ecologists but are sometimes called climagraphs or climatographs too but the concept is different a It has a better representation of climates show examples as the monthly rainfall is shown by a bar graph with months along the horizontal axis and a line graph is used to show the monthly average temperatures b This shows well the seasonal patterns of temperature change and precipitation c These diagrams may be modi ed to show or emphasize different aspects of climate such as the dry season or the frost period as shown on P 33a in the class notes Here a line graph is used for both temperature and rainfall d Smith amp Smith s 6Lh edition of your textbook uses for the first time climatic charts as devised by Walther to show typical climates of Biome types in terrestrial ecology Fig 214 but it gives no credit to the work of climatologists from which Walther had adapted this Pgs 563611 D Climatic forces 1 Patterns of global heating and rain Smiths fig 2 12 a Equatorial areas are intensely heated while in polar regions same light energy covers a much larger area the polar areas are the centers of cooling Smiths fig 27 b This unequal heating of the earth causes the atmosphere to form planetary convection cells class notes pg 33b that are called Hadley cells c Warmer air is lighter and rises cooling by adiabatic temperature change approximately 1 C 100 M 3 F 1000 ft with variations from water vapor condensation which is caused by decreases in gas density When air sinks it warms by adiabatic heating as air compresses d Convectional rain is when rising air cools and water condenses out forms clouds and may falls as rain snow hail etc P 34 in Class notes e Topographical 0r orographic rain occurs when air is forced up by mountains it cools and releases water There is often a desert on the lee side of the mountain caused by adiabatic heating which causes air to absorb water not release it The air will be warmer on the descending size due to the release of heat of condensation the wet adiabatic temperature change Smiths Fig 215 f Frontal rain is caused by a colder denser air mass forcing up a warmer lighter air mass cooling it and if the warm air is saturated water is forced to condense out as clouds and precipitation occurs P34 class notes 2 Hadley cells P33b Smiths Fig 28 a The equatorial Hadley cell forms in response to the intense heating of air Hot rising air cools and water condenses into clouds often with daily convectional rain Because air rises aloft there s little horizontal wind and so these areas in the cell are called the equatorial doldrums recalling that in the time of sailing vessels that here there is no wind no horizontal movement of air However rain is frequent as the light low pressure air is rising aloft so the custom arose to party and celebrate when crossing the equator Fquot In response to the rising air air in the equatorial cell is pulled along the surface toward the equator This causes the Horse latitude doldrums as sinking air is pulled down by gravity to replace the air moving toward the equator Adiabatic heating occurs meaning only evaporation thus little rain Horses and people died here when stuck in these doldrums in days of sailing vessels thus the Horse Latitudes The desert belts of the world are in the horse latitudes and curve into the heart of continents far from sources of water see Smiths Fig 212 c Polar Hadley cell is created in response to cold sinking air that moves away from the poles and air aloft moves toward the poles to replace the sinking arr d The third or middle Hadley or Ferrel s cell is formed by the mixing of cold air and warm air masses where the forces of heat meet forces of cold and they miX it up with highly variable results of weather More on this later 3 These Hadley s planetary convection cells give rise to the major surface winds a The surface planetary winds obey the Coriolis effect in which winds veer east or west because earth s surface moves faster toward the equator slower to the poles c Ferrel s rule determines the direction of the veer Face the direction the wind is blowing toward in the Northern Hemisphere the winds veer to the Right in the Southern Hemisphere the winds veer to the Left d You can see that the surface winds of the North Polar Hadley Cell veer right from the East thus the expression a nor easter refers to violent bitter cold air from the North In the Southern Hemisphere the polar winds veer left from the east thus a sou easter Therefore winds in the equatorial cell blowing toward the equator veer from the east and are called the trade winds because they were very reliable for sailing ships as the trade winds respond to the powerful heating of the equatorial region Surface winds blowing away from the equator and the horse latitudes veer from the west and thus are called the westerlies Because the westerlies result from the sinking air of the horse latitudes and are running into the polar easterlies these winds are therefore also called the variables as they were not reliable winds like the trades 4 Seasonal Variations See Page 34 in notes Fig 29 in Smiths a Since earth tilted about 23 12 degrees the bands of air movements swing back and forth across the equator bringing about seasonal changes in the winds b At the equinoxes spring and fall the earth s tilt is tangential to its orbit around the sun therefore the whole world has then 12 hours daylight 12 hours night c The solstices are when respective hemisphere pole points to the sun or away from the sun The summer and winter solstices mark respectively the longest and shortest days of the year for a hemisphere O Q d Arctic and Antarctic circles represent where at 23 12 degrees latitude North and South of the Poles the sun does not set on the longest day or on the shortest day it does not rise above the horizon e The Tropic of Cancer in the Northern Hemisphere and Tropic of Capricorn in the Southern Hemisphere each 23 12 degrees latitude north or south of the Equator indicates where on the longest day of the hemisphere the sun is directly overhead at noon Thus the most intense equatorial heating reaches that latitude once a year f North and South of the Equator the climate shows marked variations in rainfall in wet dry seasons The closer to the equator the longer the wet season the further from the equator the shorter the dry season which is at low sun winter period while the wet season is at high sun summer g It is viceversa on the other side of the horse latitudes in the zone of the westerlies in which there can be winter rains and summer droughts but it highly variable because of the effects of continents and oceans and the basic variability of the westerlies themselves 5 Local effects of land and water a Local maritime and continental in uences along shores brings out well the in uence of specific heats Let s look at the Texas Barrier Islands for an example b The pleasant sea breezes during the day is caused by land with its lower specific heat heating faster than water creating rising hot air over land that pulls relatively cool air off the sea At night the land breeze reverses this and rising air over water pulls air off the land across the bay and the salt water marshes and brings in the mosquitoes that were kept away by the sea breeze Mariners ships and sailboats used these breezes for sailing and they allow sail boats to get through the doldrums which is why sailing ships had to go close to land to get through the doldrums c Because of this maritime and continental climates are recognized with the maritime coastal climates more mild more rainy and less extreme the inland continental climates more extremehotter and colderand drier d Whole continents and oceans respond similarly to these differences in specific heating of land and water 6 Cyclones and Anticyclones see P 35 in class notes a Land as a continent heats up more that oceans so hot rising air develops forming a continental low or cyclone while the oceans the opposite maritime high or anticyclone develops b In the winter land cools faster so continental highs or anticyclones of C Q sinking cold air form while over oceans maritime lows or cyclones form from warm rising air Since this is a temperate zone phenomenon the westerlies move these masses of air from west to east at highly variable and chaotic rates giving rise to all the weather so characteristic of the intemperate zone Obeying Coriolis effect in the northern hemisphere cyclones spin counterclockwise anticyclones spin clockwise in the southern hemisphere viceversa cyclones spin clockwise anticyclones counterclockwise e This means that cyclones of rising air bring rain onto the east side of continents because of the warm sea currents 7 Effects of sea currents P 36 in Class notes Smiths 210 a Oceans are warmed at the equator and cooled at the pole The cold dense polar water in large part sinks and goes along the deep sea bottom keeping it cold b Warm surface water moves north from the equator to replace it and obeying the Coriolis effect forms a gyre counterclockwise in the northern hemisphere and clockwise in the southern hemisphere c This brings warm water from the tropics to northwest coasts and in the southern hemisphere to the southwest coasts warming NW Europe Alaska and Chile adding moisture into the westerlies bringing rain as they cool on continents especially when raised by mountain ranges d On east coasts warm water off shore allows cyclones to bring in wateri sometimes too much as in hurricanes e On its return toward the equator the gyre brings now refrigerated cold water south along coastal areas on the mid west coasts of continents and in horse latitudes Now the westerlies move across cold water get cooled forming fog banks and move onto hot land and can only evaporate resulting in the driest of all deserts the Namid of Africa the Atacama of Peru Baja California Morocco and NW Australia In seasonal west coasts the winter land is cold so this air can rain but in the summer the air can only warm up creating the Mediterranean climate of wet winters and dry summers as in California South Africa mid Chile Western Australia and of course around the Mediterraneanall lands of the olive grapes and wine D