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Atmosphere – Solar Radiations, Heat Budget, Temperature Inversion

Solar Radiations

  • Maximum at equator & min. at poles (Due to earth’s inclination & its spherical shape, Sunrays fall perpendicular to equator, with inclination increasing from equator to poles)
  • Larger the thickness / wideness of atmosphere, greater the scattering, reflection & absorption by the atmosphere, reducing the intensity of insolation on earth’s surface
  • As beam of sunrays falls perpendicular to equator, hence if sunrays cross 1 unit of atmosphere here then they have to cross almost 44.7 units at poles
  • That is why Insolation received per unit area is max at equator & min at poles

Specific Heat

  • Heat capacity or specific heat of water is 5 times that of earth surface
  • Which means same amount of heat will heat earth’s surface 5 times than that of water of same mass & vice-a-versa in case heat is withdrawn
  • Hence land surface heats & cool more rapidly than water surface
  • Specific Heat Energy required to raise the temperature of 1 gm of substance by 1*C
  • Rate of Heating differ between Water & Land because water is transparent to sunrays & is always in motion
  • Hence heat is absorbed more slowly as absorbed heat is distributed over a great depth & area

Heat Budget

  • Earth maintains its temp. as amount of heat received by it in form of insolation = Amount of heat radiated by it through terrestrial radiation.
  • Gain & loss of heat or balance of heat (Received & Emitted) is known as heat budget

Heat Received

  • Total Solar Radiations 100 %
  • Returned back to atmosphere in short wave form 35 % (Mainly from reflection & scattering from clouds, dust particles & from earth surface)
  • Absorbed by atmosphere (mostly water vapour + Dust + Gases) 14 %
  • Available to earth 51 % (34 % from direct sunlight & 17% from scattered radiations) Hence only 65 % of total insolation is available for heating atmosphere

 

Heat Budget

Note Clouds act generally as mirror, reflects sunlight in different directions rather than absorbing it (Reflected sunlight is permanently lost to earth)

 

Heat Radiated

  • Returned as long wave radiation form earth 51 %

 

  • 17 % radiated from earth surface
  • 34 % absorbed by atmosphere (19 % + 9 % + 6 %)

 

  • Now, 48 % ( 34 % + 14 %) absorbed by atmosphere is radiated to space by atmosphere

Hence, Total Heat Received = Total Heat Radiated

Temperature Variation

  • Under normal circumstances temperature decreases from equator to poles & each latitude has its own temp.
  • But, other factors such as altitude, oceanic currents, prevailing winds etc. also affect the temp. of a place.
  • Hence, there lies a difference b/w temp. of a place & mean temp. of its parallel Known as temperature / thermal anomaly

Temperature Variation on earth

  • If Expected temp. of a place (latitude) minus actual temp. of that place is negative then it is called negative anomaly & if positive then positive anomaly
  • Due to more land area in northern hemisphere & more water area in southern hemisphere, largest of anomalies are found in N – Hemisphere & smallest in S – Hemisphere

 

Isotherms

  • Imaginary lines joining places having equal temperatures, reduced to sea level to eliminate the effect of altitude
  • Runs almost parallel to latitudes but modified somewhat due to influence of land & sea
  • At any latitude, temperature over land mass is higher in summer & lower in winters compared to the temp. over sea
  • Hence isotherms while crossing from landmass to oceans bend a little & vice a versa
  • In January, there is winter in N – Hemisphere & summer in S – Hemisphere, means air over oceans is warmer than that over land masses in N – Hemisphere
  • Hence isotherms bend equatorward while crossing the landmasses & polewards while crossing the oceans (Vice a versa in summers in N – Hemisphere) + Same logic for S – Hemisphere
  • More water in S hemisphere results in uniform temp. mostly, hence less bends in isotherms Trend is more clear here than at N – Hemisphere
  • Distance b/w isotherms represents rate of change of temp., hence closely spaced isotherms indicate rapid change in temp. & vice versa

 

Diurnal/Daily Range of Temperature

  • Difference b/w max. temp. during day & min. during night;
  • Sufficiently high at equator & gradually decreases towards poles
  • Minimum near sea cost due to moderating effect of sea;
  • Deserts have high diurnal range of temp. as sand absorbs & radiates quicker than land surface
  • Cloud cover reduces daily range of temp. as it obstructs incoming radiations during day & outgoing radiations during night

 

Annual Range of Temperature

  • Difference b/w average temp. of hottest & coldest month of the year
  • Minimum at equator & max at poles

 


Temperature Inversion

  • Under normal conditions, temp. of atmosphere fall with altitude
  • But there are some special conditions under which temp. increases instead of decreasing with height
  • Means air near earth surface is cooler than that of higher place
  • Factors which favour this condition are Long nights, Clear sky, Stable weather, Dry air & Ice cover

Air Drainage Temperature Inversion 

  • In mountain valleys, during long winter nights, air on higher slopes cool down quickly & become dense
  • Hence move down the slope & settle down at valley bottom, pushing comparatively warmer air up
  • Sometimes temp. at valley bottom falls below freezing point & air above at higher altitude remains comparatively warm,
  • As a result, trees at lower slopes are mostly frost bitten than that of at higher slopes
  • Houses & farms in mountain valley are generally situated along the upper slopes avoiding cold & foggy valley bottoms
  • Air pollutants such as dust, smoke etc. do not disperse at valley bottom due to this reason

Air Drainage Temperature inversion

Radiation Temperature Inversion

  • In areas, where there is rapid cooling of earth surface due to intense radiation from earth’s surface
  • As a result air close to earth surface becomes cooler than air at higher elevation
  • Generally occurs in winters

Radiation Temperature Inversion

Advection Temperature Inversion

  • In areas, where warmer air blows over colder surface
  • Example Snow covered area

Advection Temperature Inversion

Frontal Temperature Inversion

  • When warm air mass rises over cold air mass
  • Generally occurs in mid latitudes where cold polar air mixes with warm subtropical air mass
  • Lots of fog is generated

Frontal Temperature Inversion

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