APPLICATIONS OF AGROMETEOROLOGY AND CLIMATOLOGYDEFINITIONS AND TERMINOLOGIES

ClimatologyMeteorologyAgricultural MeteorologyExamples of the scope of agrometeorology

Applications of weather and climate information in agricultureHYDROLOGICAL CYCLE

Processes in the hydrologic cycle Human impact on the hydrologic cycle

SESSION EARTH'S ATMOSPHEREComposition of the earth's atmosphereLayers of the earth's atmosphereComposition of the earth's atmosphereHeat transfer in the earth's atmospheric systemSolar radiation-earth's atmosphere interaction

Definitions - Climatology, Meteorology, agrometeorology, agroclimatologyClimate affects every sphere of human life including agriculture, transportation, business and commerce, safety and security and sustainable management of natural resources such as soil, water, air quality, forest, and biodiversity conservation.Some definitions and terminologiesA climatologist studies long term trends in the climate and try to forecast major long-term changes. Climatology is a study of the climate of a place or region on the basis of weather records accumulated over long periods of time. Long term changes in climate can affect energy usage, food production, survival of endangered species, health and life expectancy. The climate determines the types of plants and animals that can inhabit a particular region. The climate that you live in depends on your geographic location and altitude. It includes all of the average weather conditions that you experience on an ongoing basis.Paleoclimatologists study past climates on earth. They want to know what the conditions were like on earth hundreds, thousands, or even millions of years ago. Understanding past conditions is extremely important in predicting future conditions. Most of the climatologically studies on global warming today involve paleoclimatology.Agricultural Climatology is the branch that studies the processes and impacts of climatic factors over larger time and spatial scales.

A Meteorologist studies the current weather conditions and makes short-term forecasts about the weather, including the temperature, winds, amount and type of precipitation.Meteorology is the science of weather and it is an inter-disciplinary science because the atmosphere, land and ocean constitute an integrated system. The three basic aspects of meteorology are observation, understanding and prediction of weather. In physical meteorology we study the physical processes of the atmosphere, such as solar radiation, its absorption and scattering in the earth-atmosphere system, the radiation back to space and the transformation of solar energy into kinetic energy of air. Cloud physics and the study of rain processes are a part of physical meteorology.

Micrometeorology (crop micrometeorology or animal biometeorology) is the branch of agricultural meteorology dealing with atmospheric-biosphere processes occurring at small spatial scales and over relatively short time periods crop micrometeorology for managed vegetative ecosystems and animal biometeorology for livestock operations.

Agricultural (Agro) meteorologyA branch of meteorology that examines the effects and impacts of weather and climate on crops, rangeland, livestock, and various agricultural operations. The agrometeorologist requires not only a sound knowledge of meteorology, but also of agronomy, plant physiology and plant pathology and animal pathology, in addition to common agricultural practices. Main goals of agrometeorology are the study of the interactions between atmospheric variables with biological systems in agriculture, and applying this knowledge to increase food production and improve food quality.Biological systems in agriculture are,

a. crops, b. forests, c. soil on which the plants grow, d. animals, e. associated weeds, f. associated pests and diseases

Atmospheric variables used to characterize atmospheric conditions and may also affect biological systems are –

a. Solar radiationb. Precipitationc. Wind speed and directiond. Humiditye. Air temperaturef. Soil temperatureg. Atmospheric pressureh. Gases in the atmosphere(oxygen, carbon dioxide, methane, nitrous oxides, water vapour)

Response of biological systems to atmospheric conditionsa. observation of developmental stages in cropsb. meat yieldc. egg or milk productiond. grain qualitye. forage quality

Modified agricultural environmenta. Irrigated areasb. Greenhousesc. Animal shelters/housesd. Plant nurseriese. Mulching

Research and environmental concernsa. material use efficiency – water, nutrient and radiationb. animal comfort levels(affected by the physical environment)c. air pollution damage to cropsd. disease and pests development(as a function of the environmental conditions)e. greenhouse gas emissions by agricultural activities

Application of agrometeorology and use of weather informationWeather information and forecasts are of vital importance to many activities like agriculture, aviation, sea navigation, road transport, shipping, fisheries, tourism, business and commerce, defense, industrial projects, water management and disaster mitigation. There are other human activities which are affected by weather and for which meteorologists can provide valuable inputs. Applied meteorologists use weather information and adopt the findings of theoretical research to suit a specific application; for example, design of aircraft, control of air pollution, architectural design, urban planning, and exploitation of solar and wind energy, air-conditioning, and development of tourism. In simple terms, agricultural meteorology is the application of meteorological information and data for the enhancement of crop yields and reduction of crop losses because of adverse weather. It also has linkages with forestry, horticulture and animal husbandry.

i. Agricultural meteorology, or agrometeorology, addresses topics that often require an understanding of biological, physical, and social sciences.

ii. Agricultural meteorology studies processes that occur from the soil depths where the deepest plant roots grow to the atmospheric levels where seeds, spores, pollen, and insects may be found.

iii. Agricultural meteorologists collect and interpret weather and climate data needed to understand the interactions between vegetation and animals and their atmospheric environments.

iv. The climatic information developed by agricultural meteorologists is valuable in making proper decisions for managing resources consumed by agriculture, for optimizing agricultural production, and for adopting farming practices to minimize any adverse effects of agriculture on the environment. Such information is vital to ensure the economic and environmental sustainability of agriculture now and in the future.

v. Agricultural meteorologists also quantify, evaluate, and provide information on the impact and consequences of climate variability and change on agriculture.

vi. Increasingly, agricultural meteorologists assist policy makers in developing strategies to deal with climatic events such as floods, hail, or droughts and climatic changes such as global warming and climate variability.

vii. Agricultural meteorologists are involved in many aspects of agriculture, ranging from the production of agronomic and horticultural crops, trees, and livestock to the final delivery of agricultural products to market.

viii. They study the energy and mass exchange processes of heat, carbon dioxide, water vapor, and trace gases such as methane, nitrous oxide, and ammonia, within the biosphere on spatial scales ranging from a leaf to a watershed and even to a continent. They study, for example, the photosynthesis, productivity, and water use of individual leaves, whole plants, and fields.

i. They also examine climatic processes at time scales ranging from less than a second to more than a decade.

Significance of weather and climate for agricultureClimate conditions are different around the world - You benefit or be at the mercy of the weather. To benefit from natural factors one has to take them into account and learn to know them well.

The following decisions should not be made without knowing climate conditions:a. Land use and management - before giving recommendations about land use it is

necessary to know the environmental conditions(rainfall, solar radiation, temperature, frosts, hail etc)

b. Selecting plants and breeds of animals – in order to select plant species or varieties, a prior agroclimatologic characterization is required (weekly, daily, hourly temperature, rainfall, solar radiation, evaporation, wind speed, evapotranspiration and relative humidity). To assess the suitability of an environment to animal production knowledge of the effects solar radiation, wind, precipitation, temperature and relative humidity is essential

c. Crop production practices such as irrigation, d. pests and disease control – Moisture related parameters such as relative humidity,

rainfall and wetness or dryness duration are essential variables in most plant disease prediction schemes and also for predicting outbreaks of some insect pests

e. crop and weather relationshipsf. timing of different farm activities – sowing, ploughing, fertilizer application, pests

and disease control applications should be done when weather conditions are most favourable application of pesticides would be unsuccessful under rainy, windy conditions

Climate change impact on agricultureFood cropsCash cropsAnimal production (meat, eggs, milk)Incidence of pests and diseasesIrrigationFactors affecting the weather/climate of a placeThere are a number of factors that affect the climate of a particular place in the world. These are:

a. latitudeb. ocean currentsc. windd. altitude/e. relieff. nearness to water bodies

The combination of these factors is what gives every place on earth its own distinct climateLatitude

Latitude controls the amount of solar radiation that reaches the surface of the earth. The general rule for latitude is that the farther away from the equator you are the less energy that is reaching the ground at any point in timeThis is due to two factors:a. The angle at which the sun's rays are positioned to the surface of the earth based on its

curvatureb. The amount of atmosphere that the light has to travel through at a particular latitude c. As latitude increase the angle at which the sun's rays hit the ground decreasesd. This effect is amplified by the tilt of the Earth and the resultant seasons This means that the same amount of energy coming from the sun is spread out over a greater

area This leads to decreased temperatures and evaporation rates at higher latitudes As the thickness of atmosphere increases the amount of absorption, scattering, and reflection

increases leading to a corresponding decrease in light reaching the ground The differential heating of the land, air, and water produced by these latitudinal variations

leads to the creation of global winds and ocean currentsOcean Currents

a. Throughout the world's oceans there are three dimensional underwater rivers that circulate water all over the globe

b. The water in these currents differs from their surroundings due to differences in their temperatures and chemical composition

c. They are driven by wind, and differences in temperature and salinityd. Ocean Currents can move vast amounts of watere. These currents play an important role in the global redistribution of heat and the

moderation of climates all over the world f. Warm currents heat the air above the water causing a milder wetter climate even at higher

latitudesg. Cold currents lead to cold dry climates, due to the fact that cold air cannot evaporate as

much water as warm

Windsa. Wind is caused by differences in pressure resulting from differential heating of the

earth’s surfaceb. As the air molecules are heated they move more rapidly decreasing the density of an air

mass and it risesc. Warmer air is also able to hold more water vapour than cold air so it is more moistd. Areas of warm rising air have low pressurese. Winds result from the earth trying to equalize pressure from areas of high pressure to

those with a low pressure across a pressure gradient. An example of this is off and on shore breezes

f. Theoretically, global wind patterns would be two large convection cells with warm air rising at the equator and falling at the poles which in turn would flow back to the equator

g. However, other forces affect the rising and falling of air on the earth’s surface (ex Coriolis Force)

h. The Coriolis Force deflects wind to the right in the northern hemisphere and to the left in the southern

i. Convection cells form where warm air coming from the equator meets cold air moving in the opposite direction creating a high pressure system as the air sinks

j. These subtropical highs occur at approximately 30o and polar fronts occur at approximately 60o

k. The descending air of the subtropical highs leads to two wind patterns on the surface, the trade winds (blowing towards the equator) and the westerlies (blowing towards the poles)

l. The trade winds converge near the equator and rise as they are heated creating the area known as the InterTropical Convergence Zone (ITCZ) or doldrums

m. The westerlies meet winds coming from the polar fronts which forces air up creating the subpolar low

n. These movements lead to three distinct cells of air circulation in each hemisphere

Elevation As altitude increases, the corresponding temperature of air decreases It decreases at the environmental lapse rate of 6.4oC/1000m Solar radiation only turns into heat when it is absorbed by a body of matter Lower down in the atmosphere the air is denser and contains more water vapour, air

molecules, dust etc. Therefore more energy can be absorbed and turned into heat (longwave radiation) at lower

elevations Heat from the surface of the earth moves up through longwave radiation and convection

currents (called sensible heat flux)

Reliefa. Mountains form a natural barrier that cause air masses to riseb. As air is forced to rise it expands as gravity decreases, it becomes less dense and coolsc. As air rises from the ground it cools at the Dry Adiabatic Lapse Rate (DALR) which is

10oC/1000m d. Eventually it will reach an altitude where the moisture in the air condenses forming clouds

(Condensation Level) and it will then cool at the Saturated Adiabatic Lapse Rate (SALR) which is about 4.5oC/1000m

e. The SALR is less than the DALR because as moisture condenses heat is released, which slows the cooling

f. As air descends the other side of the mountain it will become unsaturated and the temperature will increase at the DALR

Nearness to Water bodiesa. Water bodies provide a source of moisture for the land masses of the worldb. Water bodies also have a moderating affect on the climates of the land masses near to themc. Insolation is unable to penetrate the lithosphere unlike water so it can only heat the surface of the land

d. Water can heat to some depth because of penetration of light and circulation within the water bodies

e. Because of this land can heat up or cool down much quicker than water, so the water has a moderating effect on the land around it

Hydrologic cycleWater exists in three states: liquid, solid and invisible vapour.The hydrologic cycle is a conceptual model that describes the storage and movement of water between the biosphere, atmosphere, lithosphere, and the hydrosphere. Water on this planet can be stored in any one of the following reservoirs: atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, groundwater, plants and other living organisms. The hydrologic cycle consists of inflows, outflows, and storage. Inflows add water to the different parts of the hydrologic system, while outflows remove water. Storage is the retention of water by parts of the system.

Figure1: Hydrologic Cycle.Water is continually cycled between its various reservoirs through the processes of evaporation, condensation, precipitation, deposition, runoff, infiltration, sublimation, transpiration, melting, and groundwater flow. The driving force for the hydrologic cycle is the sun, which provides the energy needed for evaporationThe oceans supply most of the evaporated water found in the atmosphere. Of this evaporated water, only 91% of it is returned to the ocean basins by way of precipitation. The remaining 9% is transported to areas over landmasses where climatological factors induce the formation of precipitation. The resulting imbalance between rates of evaporation and precipitation over land and ocean is corrected by runoff and groundwater flow to the oceans.Approximately 97% of all the water on the Earth is in the oceans. The other 3% is held as freshwater in glaciers and icecaps, groundwater, lakes, soil, the atmosphere, and within life.

Distribution of water on the surface of the earthTable1: Inventory of water at the Earth's surfaceReservoir Volume (cubic km x 1,000,000) Percent of Total Oceans 1370 97.25 Ice Caps and Glaciers 29 2.05 Groundwater 9.5 0.68 Lakes 0.125 0.01 Soil Moisture 0.065 0.005 Atmosphere 0.013 0.001Streams and Rivers 0.0017 0.0001Biosphere 0.0006 0.00004

Table 2: Typical residence times of water found in various reservoirs  Reservoir Average Residence Time  Glaciers  20 to 100 years  Seasonal Snow Cover  2 to 6 months  Soil Moisture  1 to 2 months  Groundwater: Shallow  100 to 200 years  Groundwater: Deep  10,000 years  Lakes  50 to 100 years  Rivers  2 to 6 months

Processes in the hydrological cycleThe hydrologic cycle is the set of processes by which water moves through different reservoirs on earth. Studies indicate that the amount of water on earth is constant helped lead to the concepts of the hydrologic cycle. The hydrologic cycle influences climate and weather patterns and thus changes as global climate changes. The hydrologic cycle is driven primarily by energy from the sun because the oceans are the largest reservoir of liquid water that is where most evaporation occurs. The amount of water vapour in the air varies widely over time and from place to place; we feel these variations as humidity.The largest reservoir by far is the oceans, which hold about 97% of the earth’s water. The remaining 3% is the freshwater so important to our survival, but about 78% of that is stored in ice in Antarctica and Greenland. About 21% of freshwater on the earth is groundwater, stored in sediments and rocks below the surface of the earth. The freshwater that we see in rivers, streams, lakes, and rain is less than 1% of the freshwater on the earth and less than 0.1% of all the water on the earth.

Groundwater flowWhere water infiltrates the ground, gravity pulls the water down through the pores until it reaches a depth in the ground where all of the spaces are filled with water. At this point, the soil or rock becomes saturated, and the water level which results is called the water table. The water table is not always at the same depth below the land surface. During periods of high precipitation, the water table can rise. Conversely, during periods of low precipitation and high evapotranspiration, the water table falls. The area below the water table is called the saturated zone, and the water in the saturated zone is called groundwater. The area above the water table is the unsaturated zone.

Groundwater is found in aquifers which consist of soil or rock in the saturated zone that can yield significant amounts of water. In an unconfined aquifer the top of the aquifer is defined by the water table. Confined aquifers are bound on the top by impermeable material, such as clay. Water in a confined aquifer is normally under pressure and can cause the water level in a well to rise above the water table. If the water rises above the ground surface it is designated a flowing artesian well. A perched water table occurs when water is held up by a low permeability

material and is separated from a second water table below by an unsaturated zone. In the saturated zone, groundwater flows through the pores of the soil or rock both laterally and vertically. Water moving from an aquifer and entering a stream or lake is called groundwater discharge, whereas any water entering an aquifer is called recharge. In Michigan, groundwater typically discharges from aquifers to replenish rivers, lakes, or wetlands. An aquifer may receive recharge from these sources, an overlying aquifer, or more commonly from precipitation followed by infiltration. The recharge zone is that area, either at the surface or below the ground, which provides water to an aquifer and may encompass most of the watershed.

Because water movement is cyclical, an inflow for one part of the system is an outflow for another. Looking at an aquifer as an example, percolation of water into the ground is an inflow to the aquifer. Discharge of ground water from the aquifer to a stream is an outflow (also an inflow for the stream). Over time, if inflows to the aquifer are greater than its outflows, the amount of water stored in the aquifer will increase. Conversely, if the inflows to the aquifer are less than the outflows, the amount of water stored decreases. Inflows and outflows can occur naturally or result from human activity.

EvaporationEvaporation is the change of state in a substance from a liquid to a gas. In meteorology, the substance we are concerned about the most is water. For evaporation to take place, energy is required. The energy can come from any source; the sun, the atmosphere, the earth, or objects on the earth such as humans. Everyone has experienced evaporation personally. When the body heats up due to the air temperature or through exercise, the body sweats, secreting water onto the skin. The purpose is to cause the body to use its heat to evaporate the liquid, thereby removing heat and cooling the body. It is the same effect that can be seen when you step out of a shower or swimming pool. Evaporation is the process whereby liquid water is converted to water vapour (vaporization) and removed from the evaporating surface (vapour removal). Water evaporates from a variety of surfaces, such as lakes, rivers, pavements, soils and wet vegetation.

TranspirationTranspiration is the evaporation of water from plants through stomata. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. In most plants, transpiration is a passive process largely controlled by the humidity of the atmosphere and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process of the plant. The remaining 99% is passed into the atmosphere. The combination of two separate processes whereby water is lost on the one hand from the soil surface by evaporation, from plant surfaces and on the other hand from the internal structure of crops through the stomata pores by transpiration is referred to as evapotranspiration (ET). Transpiration consists of the vaporization of liquid water contained in plant tissues and the vapour removal to the atmosphere. Crops predominately lose their water through stomata. These are small openings on the plant leaf through which gases and water vapour pass.

Significance of TranspirationAdvantages1. Rapid transpiration increases the absorption of water.2. Transpiration helps in upward movement of water and minerals through xylem ducts.3. Transpiration has a cooling effect on plants in presence of excess of solar energy.

Disadvantages1. When the transpiration rate is high and soil is deficient in water, plants face internal water deficit (wilting).2. Extra structural modifications cause a burden on plants.

The rate of transpiration in a part is an indirect measure of rate of photosynthesis, as it indicates the degree and period of stomata opening.

CondensationCondensation is the process whereby water vapor in the atmosphere is returned to its original liquid state. In the atmosphere, condensation may appear as clouds, fog, mist, dew or frost, depending upon the physical conditions of the atmosphere. Condensation is not a matter of one particular temperature but of a difference between two temperatures; the air temperature and the dew point temperature.

PrecipitationPrecipitation is the result when the tiny condensation particles grow too large, through collision and coalesce, for the rising air to support, and thus fall to the earth.

RunoffRunoff occurs when there is excessive precipitation and the ground is saturated (cannot absorb anymore water). This runoff flows into streams and rivers and eventually back into the sea. Evaporation of this runoff into the atmosphere begins the hydrologic cycle over again. Some of the water percolates into the soil and into the ground water only to be drawn into plants again for transpiration to take place.

Humans and the hydrologic cycleThe properties of water and the hydrologic cycle are largely responsible for the circulation patterns we see in the atmosphere and the oceans on the earth. Atmospheric and oceanic circulations are two of the major factors that determine the distribution of climatic zones over the earth. Changes in the cycle or circulation can result in major climatic shifts. For example, if average global temperatures continue to increase as they have in recent decades, water that is currently trapped as ice in the polar ice sheets will melt, causing a rise in sea level. Water also expands as it gets warmer, further exacerbating sea level rise. Additionally, the acceleration of the hydrologic cycle (higher temperatures mean more evaporation and thus more precipitation) may result in more severe weather and extreme conditions. Groundwater can take thousands or millions of years to recharge naturally, and we are using these resources far faster than they are being replenished. Understanding the hydrologic cycle is basic to understanding all water and is a key to the proper management of water resources. Water vapor is transported by winds and air currents through

the atmosphere. When the air mass cools sufficiently, the water vapor condenses into clouds, and a portion falls to the ground as precipitation in the form of snow, rain, sleet, or hail. Water that falls to the ground as precipitation follows many paths on its way back to the atmosphere. The water may be intercepted and taken up by plants; it may be stored in small depressions or lakes; it can infiltrate the soil; or it can flow over the surface to a nearby stream channel. The sun may cause the water to evaporate directly back into the atmosphere, or the force of gravity may pull it down through the pores of the soil to be stored for years as slowly moving groundwater. Some of the water flowing through the ground returns to the surface to supply water to springs, lakes, and rivers. Water on the ground surface, in streams or in lakes can return to the atmosphere as vapor through the process of evaporation. Water used by plants may return to the atmosphere as vapor through transpiration which occurs when water passes through the leaves of plants. Collectively known as evapotranspiration, both evaporation and transpiration occur in greatest amounts during periods of high temperatures and wind, dry air, and sunshine.

Role of Soils in the hydrologic cycleAs water reaches the land surface, it can seep downward through pores between soil particles. Soil is made up of tightly packed particles of many shapes and sizes. A high porosity soil has the ability to hold large amounts of water due to the presence of many pore spaces. If the pores are well connected and allow water to flow easily, the soil is permeable. The size and shape of clay particles along with the arrangement of the pores between these particles result in clay soils being relatively impermeable and resistant to infiltration. Sands and gravels allow more rapid infiltration due to their high permeability. The initial water content of the soil is also important. In general, water infiltrates drier soils more quickly than wet soils. The intensity of a storm, or the length of time during which precipitation occurs, can also influence infiltration. If rain or snowmelt reaches the soil surface faster than it can seep through the pores, then the water pools at the surface, and may run downhill to the nearest stream channel. This limitation on the soil's capacity to allow infiltration is one of the reasons why short, high intensity storms produce more flooding than do lighter rains over a longer period of time.

Surface Runoff and WatershedsThe portion of water which does not infiltrate the soil but flows over the surface of the ground to a stream channel is called surface runoff. Water always takes the path of least resistance, flowing downhill from higher to lower elevations, eventually reaching a river or its tributaries. All of the land which eventually drains to a common lake or river is considered to be in the same watershed. Watersheds are defined by topographic divides which separate surface flow between two water systems. Land use activities in a watershed can affect the water quality of surface water as contaminants are carried by runoff and of groundwater, especially through infiltration of pollutants. Understanding the factors which influence the rate and direction of surface water and groundwater flow helps to determine where good water supplies exist and how contaminants migrate.

AtmosphereThe atmosphere surrounds the earth. It is made up of a body of air or gasses that protects the planet and supports life and climate processes.

HydrosphereThe hydrosphere is composed of all of the water on or near the earth. This includes the oceans, rivers, lakes, and even the moisture in the air. Ninety-seven percent of the earth's water is in the oceans. The remaining three percent is fresh water; three-quarters of the fresh water is solid and exists in ice sheets

BiosphereThe biosphere is composed of all living organisms. Plants, animals, and one-celled organisms are all part of the biosphere. Most of the planet's life is found from three meters below the ground to thirty meters above it and in the top 200 meters of the oceans and seas.

Layers of the atmosphereTroposphere: The layer of the atmosphere closest to the earth is the troposphere. This layer is where weather occurs. It begins at the surface of the earth and extends out to about 4-12 miles. The temperature of the troposphere decreases with height. This layer is known as the lower atmosphere.

a. Vertical mixing of air and water vapor generates “weather.”b. Greenhouse gases, primarily H2O, CO2 and CH4, regulate surface temperatures.c. 50% of total atmospheric mass is contained below

Stratosphere: Above the troposphere is the stratosphere, which extends to about 15-50 km above the earth's surface. Temperature rises within the stratosphere but still remains well below freezing. Photochemical reactions produce ozone; ozone UV absorption increases temperature.

Mesosphere: From about 56 to 80 km above the surface of the earth lies the mesosphere, where the air is especially thin and molecules are great distances apart.

Thermosphere : The thermosphere rises several hundred miles above the earth's surface, from 80 km up to about 644 km. Oxygen molecules absorb short-wave solar radiation, which results in heating.

Exosphere: Extending from the top of the thermosphere to 10,000 km above the earth is the exosphere. This layer has very few atmospheric molecules, which can escape into space.

Composition of the atmosphereThe atmosphere is the body of air which surrounds our planet. Most of our atmosphere is located close to the earth's surface where it is most dense.

Table 1 Atmospheric constituentsConstituent Relative percentage of dry air (%)Nitrogen 78.08Oxygen 20.00Argon 0.934Carbon dioxide 0.036

Neon 0.0018Helium 0.0005Methane 0.00017Hydrogen 0.00005Nitrous 0.00003Ozone 0.000004

** In addition, water vapour is variable but typically makes up about 1-4% of the atmosphere.The role of the ozone layerOzone plays a key role in sustaining life on earth. It absorbs UV radiation that is harmful to biological molecules (such as DNA, proteins, other nucleic acids). Yet ozone forms only a minute fraction of the total atmosphere. If all the ozone was collected from the stratosphere and brought down to the surface of the earth it would form a surface layer 2-3 cm thick. Ozone is now being destroyed by the increasing concentration of man-made chemicals such as CFCs (chlorofluorocarbons) and nitrogen oxides such as NOx and N2O.in the upper atmosphere.

ACTIVITYa. Students are supposed to define and explain the various processes in the

hydrological cycleb. Students should be able to determine the impact of human activities on the

hydrological cycle. e.g. the construction of a dam, road construction, surface miningc. A water reservoir has a surface area of 20 km2 and the evaporation rate in the

location is 0.5 mm per day. Estimate the amount of water lost per day; per year expressed in volumetric terms.

d. Students should be able to identify the layers of the atmosphere(troposphere, stratosphere, mesosphere, thermosphere and exosphere

e. What is the structure and composition of the atmosphere?f. How does solar energy influence the atmosphere?g. How does the atmosphere interact with land and oceans?h. How is heat transferred throughout the earth system?

Heat transfer in the atmospheric systemsThere are three methods of heat transfer: radiation, conduction, and convection.Radiation is the method by which the sun's energy reaches the earth and travels in the form of (electromagnetic) waves. The following are characteristics of radiative heat transfer:

a. The radiative heat transfer process is independent of the presence of matter. It can move heat even through empty space.

b. All bodies emit radiation and the wavelength (or frequency) and energy characteristics (or spectrum) of that radiation are determined solely by the body's temperature.

c. The energy flux drops as the square of distance from the radiating body.d. Radiation goes through a transformation when it encounters other objects (solid, gas or

liquid).

e. That transformation depends on the physical properties of that object and it is through this transformation that radiation can transfer heat from the emitting body to the other objects.

f. Radiant energy is released when an object absorbs the radiation, resulting in the transfer of heat.

Conduction is the direct transfer or movement of warmth and energy from one molecule to another molecule by collision. In conduction, the faster molecules are moving, the hotter the substance will be. Conduction is the transfer of heat from one substance to another by molecular interactions (i.e. heat transfer by molecules actually touching). Heat transfer by conduction always flows from a higher temperature source/object to lower temperature source/object. Examples: grabbing a hot pan with your hand, warming up a cold metal spoon by holding it, cooling off by sitting in a cold bath.

Convection is the organized motion or movement of large groups of molecules based on their relative densities or temperatures. Convection is happening when warm air rises and cold air sinks. Convection is the transfer of heat due to motions of a fluid. In the atmosphere, convection is the vertical mixing of warm air upward and cold air downward. Examples: thermals rising on a warm day, putting your face above a flame and feeing the hot air rising into your face. The transport of heat air or water by horizontal winds is usually referred to as advection. Warm advection brings warm air into a region. Cold advection brings cold air into a region. Moisture advection brings moister air and is usually combined with warm advection. Latent heat is the “hidden heat” that is either absorbed or released when a substance undergoes a change of state. Latent heat is absorbed when a substance moves from a lower energy state to a higher energy state (examples: melting, evaporation, sublimation). The net effect is that this state change acts to cool the surrounding environment. Latent heat is released when a substance moves from a higher energy state to a lower energy state (examples: condensation, freezing, deposition.

Global average components of the earth’s energy balance

Factors affecting the energy balance of the earth and its temperaturea. The total energy influx, which depends on the earth's distance from the sun and on solar

activity b. The composition of the atmosphere c. Albedo, the ability of the earth's surface to reflect light

Temperature is the measure of the degree of hotness or coldness of a body. It is also a measure of kinetic energy of atoms and molecules. Heat is the measure of energy in the process of being transferred from one object to another because of the temperature difference between the objects.

Characteristics of energy from the sunRadiation is the method by which the sun's energy reaches the earth and travels in the form of (electromagnetic) waves. Radiation or heat waves pass most easily through a vacuum. Radiant energy is released when an object absorbs the radiation, resulting in the transfer of heat. Examples: the sun warming your face on a sunny day, a fire glowing red, the Greenhouse Effect.

a. The solar energy travels through space in the form of electromagnetic waves enabling the transfer of heat through radiation.

b. All bodies emit radiation and that the wavelength and energy characteristics of that radiation are determined by the body’s temperature(Wien’s Displacement Law)

c. The radiant energy drops with the square of distance from the radiating body(Inverse square law)

d. Radiation goes through a transformation when it encounters other objects(solid, gas or liquid)

Laws of radiation – the magnitude and quality of solar radiation depends on temperature level.

a. Wien’s Displacement Law

λ peak = αT

α is a constant equal to 2897 (units μ m K ) (1 μ m = 10−6 m )T the temperature of the radiating object in units of Kλ peak wavelength of the energy emitted.Calculate the peak wavelength of radiation emitted by the sun at a surface temperature of 5700K.

b. Speed of the wave c = λ ν (wavelength× frequency)c. Stefan-Boltzman Law

The surface irradiance E of an objectE = ε σ T 4

T the temperature of the radiating object in Kelvinε − emissivity determines how well a surface can absorb or emit energy (0 < ε ≤ 1 )σ - Stefan-Boltzman Constant 5 .67× 10 −8 W /m2 K 4

Calculate surface irradiance E of the sun for a surface temperature of 5700 K and emissivity of 1Inverse square LawThe Inverse Square Law is used to calculate the decrease in radiation intensity due to an increase in distance from the radiation source. Inverse Square Law:4 π RSUN

2

4 π r EARTH2 =

IEARTH

ESUN IEARTH = Irradiance at the surface of any planetary object e.g. EarthESUN = Irradiance at the surface of the object (Sun)

R= 6.96 x 105 km = Radius of the Sun (4 π R2= surface area of the object)

r = 1.5 x 108 km =Average Sun-Earth Distance (4 π r2= surface area of the outer sphere)

In order to calculate the solar constant the following equation is used:

I = ESUN ( RSUN

r EARTH)

2

IEARTH also known as Solar constantCalculate the solar constant based on data given.

Solar Constant - Is the amount of energy received at the top of the Earth's atmosphere on a surface oriented perpendicular to the Sun’s rays (at the mean distance of the Earth from the Sun). The generally accepted solar constant of 1368 W/m2 is a satellite measured yearly average.Solar radiation - atmosphere interactionEverything in nature emits electromagnetic energy, and solar radiation is energy emitted by the sun.

The energy of extraterrestrial solar radiation is distributed over a wide continuous spectrum ranging from ultraviolet to infrared rays. In this spectrum, solar radiation in short wavelengths (0.29 to 3.0 µm) accounts for about 97 percent of the total energy.

Solar radiation is partly absorbed, scattered and reflected by molecules, aerosols, water vapor and clouds as it passes through the atmosphere. The direct solar beam arriving directly at the earth’s surface is called direct solar radiation. The total amount of solar radiation falling on a horizontal surface (i.e. the direct solar beam plus diffuse solar radiation on a horizontal surface) is referred as global solar radiation.

Direct solar radiation is observed from sunrise to sunset, while global solar radiation is observed in the twilight before sunrise and after sunset, despite its diminished intensity at these times. InstrumentationActinometer is the general name for any instrument used to measure the intensity of radiant energy, particularly that of the sun. Actinometers are classified according to the quantities that they measure: A pyrheliometer measures the intensity of direct solar radiation. It is so designed that it measures only the radiation from

the sun's disk (which has an apparent diameter of ½°) and from a narrow annulus of sky of diameter 5° around the sun's disk.

A pyranometer measures global radiation (the combined intensity of direct solar radiation and diffuse sky radiation). It measures solar irradiance from the solid angle 2pi onto a plane surface. When mounted horizontally facing upwards it measures global solar irradiance. If it is provided with a shade that prevents beam solar radiation from reaching the receiver, it measures diffuse solar irradiance.

A pyrgeometer measures the effective terrestrial radiation. It measures the atmospheric infrared radiation spectrum that extends approximately from 4.5 µm to 100 µm.

A multi-filter rotating shadowband radiometer measures direct normal, diffuse horizontal and total horizontal solar irradiance.A radiometer is an instrument designed to measure the radiated electromagnetic power. When used in solar energy applications, it is usually desirable for radiometers to respond the same to equal amounts of energy at all wavelengths over the wavelength range of the radiation to be measured. Most radiometers therefore work by using a thermopile to measure the temperature rise of a sensitive element whose receiving surface is painted dull black. Instruments for measuring solar irradiance using a photovoltaic cell as the sensitive element have a non-uniform spectral response.An alternative method of measuring solar radiation, which is less accurate but also less expensive, is a sunshine recorder. Sunshine recorders measure the number of hours in the day during which the sunshine is above a certain level (typically 200 mW/cm2). Data collected in this way are used to determine the solar insolation by comparing the measured number of sunshine hours to those based on calculations and including several correction factors.

The primary instrument used to measure global solar irradiance is the pyranometer, which measures the sun’s energy coming from all directions in the hemisphere above the plane of the instrument directions in the hemisphere above the plane of the instrument• The measurement is of the sum of the direct and the diffuse solar irradiance and is called the global solar irradianceEffects of the Atmosphere and the EarthThe processes affecting the intensity of solar radiation that are important in solar energy work are scattering, absorption, and reflection. Reflection occurs in the atmosphere and on the Earth's surface.The scattering of solar radiation is mainly by molecules of air and water vapor, by water droplets, and by dust particles. This process returns about 6% of the incident radiation to space, and about 20% of the incident radiation reaches the Earth's surface as diffuse solar radiation.Three atmospheric processes modify the solar radiation passing through our atmosphere destined to the Earth's surface, namely scattering, absorption, and reflection. These processes act on the radiation when it interacts with gases and suspended particles found in the atmosphere. The process of scattering occurs when small particles and gas molecules diffuse part of the incoming solar radiation in random directions without any alteration to the properties (i.e.wavelength of the electromagnetic energy. Scattering does, however, reduce the amount of incoming radiation reaching the Earth's surface. A significant proportion of scattered shortwave solar radiation is redirected back to space. The amount of scattering that takes place is dependent on two factors: 1) wavelength of the incoming radiation; and 2) the size of the scattering particle or gas molecule. In the Earth's atmosphere, the presence of a large number of particles with a size of about 0.5 microns results in shorter wavelengths being preferentially scattered. This factor also causes our sky to look blue because this color corresponds to those wavelengths that are best diffused. If scattering did not occur in our atmosphere the daylight sky would be black.The absorption of solar radiation is mainly by molecules of ozone and water vapor. Absorption by ozone takes place in the upper atmosphere at heights above 40 km. It occurs mainly in the ultra-violet region of the spectrum, where it is so intense that very little solar radiation of wavelength less than 0.3µm reaches the Earth's surface. About 3% of the solar radiation is absorbed in this way. At low levels in the atmosphere about 14% of the solar radiation is absorbed by water vapor, mainly in the near infra-red region of the spectrum. Clouds absorb very little solar radiation, which explains why they do not evaporate in sunlight. The effect of clouds on solar radiation is mainly scattering and reflection.There is a small amount of absorption of solar radiation by oxygen. The absorption of solar radiation by carbon dioxide is also slight, although the absorption and emission of long-wave atmospheric radiation by carbon dioxide is important in the greenhouse effect.

The reflection of solar radiation depends on the nature of the reflecting surface. The fraction of the solar irradiation that is reflected from the surface of the Earth is called the albedo of the surface. As solar radiation passes through the atmosphere, the molecules in the atmosphere absorb some wavelengths strongly, resulting in a very different spectrum at ground level from that in space. Reflection occurs in the atmosphere and on the Earth's surface.

a. The scattering of solar radiation is mainly by molecules of air and water vapor, water droplets, and dust particles without any changes in the wavelength of the electromagnetic energy. Scattering however reduces the amount of incoming radiation reaching the earth’s surface.

i. Thus scattering is responsible for the blueness of the sky. ii. The scattering process returns about 6% of the incident radiation to space, and

about 20% of the incident radiation reaches the Earth's surface as diffuse solar radiation.

b. The absorption of solar radiation is mainly by molecules of ozone and water vapor. i. Absorption by ozone takes place in the upper atmosphere at heights above 40 km.

ii. It occurs mainly in the ultra-violet region of the spectrum, where it is so intense that very little solar radiation of wavelength less than 0.3µm reaches the Earth's surface.

iii. About 3% of the solar radiation is absorbed in this way.iv. Absorption 19 units by the atmosphere and 3 units by clouds to totaling 22 unitsv. Clouds absorb very little solar radiation, which explains why they do not evaporate in

sunlight. vi. The effect of clouds on solar radiation is mainly scattering and reflection.

vii. There is a small amount of absorption of solar radiation by oxygen. viii. The absorption of solar radiation by carbon dioxide is also slight, although the

absorption and emission of long-wave atmospheric radiation by carbon dioxide is important in the greenhouse effect.

c. Transmission

Irradiance - The amount of electromagnetic energy incident on a surface per unit time per unit area. When measuring solar irradiance (via satellite), scientists are measuring the amount of electromagnetic energy incident on a surface perpendicular to the incoming radiation at the top of the Earth's atmosphere, not the output at the solar surface.Direct normal irradiance is the radiation coming direct from the sun that reaches the earth.

Diffuse radiation is the scattered radiation that reaches the earth's surface. Some radiation is also scattered off the earth's surface and then re-scattered by the atmosphere to the observer. This amount can be significant in areas in which the ground is covered with snow.

Global irradiance is the total solar radiation on a horizontal surface. It is the sum of incident diffuse radiation and the direct normal irradiance projected onto the horizontal surface.

Albedo

The reflection of solar radiation depends on the nature of the reflecting surface. The fraction of the solar irradiation that is reflected from the surface of the Earth is called the albedo of the surface. The fraction of radiation reflected is called the planetary albedo, often denoted by the symbol a. Most of the reflection in our atmosphere occurs in clouds when light is intercepted by particles of liquid and frozen water (ice). The reflectivity or albedo of the Earth’s surface varies with the type of material that covers it.

Table 3 Albedo of surfacesSurface Reflectivity/Albedo

Fresh snow 0.75 - 0.9Old Snow 0.4 - 0.7

Grass 0.17 - 0.28Maize 0.18 - 0.22

Rain forest 0.12Wet dark soil 0.08Dry dark soil 0.13

Dry sand 0.35Earth(average) 0.30

Water 0.10Clouds 0.5 – 0.9

The solar spectrum

ASSIGNMENT – INSERT THE SOLAR SPECTRUM HERE!!!!!!!

a. Solar radiation is classified according to the radiation wavelengths into several regions or bands.

b. The solar spectrum covers a wide range of wavelengths from the ultra-violet to the infra-red.

c. Solar radiation consists of a bundle of radiant energy of different wavelengthsd. It is a form of electromagnetic wavese. The solar spectrum covers a range of wavelengths from the ultra-violet to the infrared

f. Ultra Violet (0.2 – 0.39 μ m ) rays produce photochemical effects which can damage genetic material e.g. bleaching, sunburns, cancer in the skin etc and forms about 9% of energy from the sun. As the sunlight passes through the atmosphere, a large portion of the ultra violet radiation is absorbed and scattered

g. Infrared (0.78 – 4.0 - 100 μ m ) has some photochemical effects, sensible on the skin as heat, used by reptiles for body temperature regulation and forms about 50%

Most of the ultra-violet (wavelength less than 370nm) is absorbed and does not reach the ground. This radiation is quickly absorbed by atoms and molecules that become ionised or dissociated. (UV range) + AB A+ + B + e-

(or AB+ + e-)1. At wavelengths close to 300nm, ozone starts absorbing UV radiation and

continues to do so down to wavelengths of about 200nm. The result is a cutoff in the wavelength of radiation reaching the ground at about 300nm.

2. Between 250nm and 200nm oxygen absorbs radiation effectively, producing oxygen atoms.

3. For wavelengths less than 150nm, ionisation processes dominate.

h. The visible portion of the solar radiation appears as light and it is made up of the following colours and their wavelengths

Table 2 the visible spectrum

Colour Wavelength μ mViolet and

Indigo0.4 – 0.435

Blue 0.435 – 0.49Green 0.490 – 0.574Yellow 0.574 – 0.595Orange 0.595 – 0.626

Red 0.626 – 0.750

Class exerciseEffective temperature of the earthThe ideas about black bodies matter because (i) the sun emits as though it were a black body with a (surface) temperature of about 6000K (ii) the earth, clouds, behave as black bodies with appropriate temperatures.

Assuming that the earth emits terrestrial radiation as a spherical black body of radius RE and temperature TE, then from the Stefan-Boltzmann relation, the total power output of the planet is 4RE

2TE4.

The rate of absorption of radiation from the sun is S(1-a) RE2 where a is the albedo (in fact, the

integral absorptivity of the earth) and S the solar constant. These must balance, and so 4RE

2TE4 = S(1-a) RE

2 (10)from which we can evaluate the effective temperature of the earth as

T E=( S (1−a )

4 σ )1/4

(11)Note that TE is independent of the radius of the body. Given that a = 0.30 and S = 1353Wm-2, we find TE = 251K (-220C). This is a bit on the cold side; the mean temperature at the surface of the earth is 288K (+150C). The problem is that we have neglected the atmosphere entirely; in particular we have neglected the internal energy transfers between the atmosphere and the surface. In effect we have considered the interface between the atmosphere and space and ignored the interface between the atmosphere and the ground.

Basic Parts of the Radiation Budget Solar Incident Energy Solar Reflected Energy Earth Emitted Energy

Incoming solar radiation is absorbed by the Earth's surface, water vapor, gases, and aerosols in the atmosphere. This incoming solar radiation is also reflected by the Earth's surface, by clouds, and by the atmosphere. Energy that is absorbed is emitted by the Earth-atmosphere system as longwave radiation.