Heat Balance of the Earth Atmosphere System Heat Sources and Sinks

10.1 Introduction - definition of heat sources and sinks

We showed in Chap. 8 that the intensity of the incoming solar radiation at the earth's surface varies widely with latitude and the transmissivity of the overlying atmosphere, being, in the annual mean, maximum at the equator and minimum at the poles. As against this and as shown by measurements and computations, the intensity of the outgoing longwave radiation varies only slightly with latitude. Thus, the difference between the incoming and the outgoing radiation creates a diabatic heat source over the equatorial latitudes and a heat sink over the polar-regions. In order that the equatorial region may not continually warm up and the polar region continually cool down, excess heat from the equatorial region must flow out to the polar region for a heat balance between the two regions. In the present text, we define a diabatic heat source or heat sink by the following criteria:

where H is the mean heat content of a unit mass of air over a region at a given time t and V is Del operator.

Simpson (1928, 1929) in England appears to have been one of the first to have carried out a detailed computation of the heat budget of the earth-atmosphere system, using method and data which produced surprisingly realistic results. Some details of his method and findings will be reviewed in this chapter.

After the introduction of the earth-observing satellites in the sixties and seventies of the last century there was renewed interest in the subject and direct measurements were made from space platforms of the intensities of the incoming solar radiation, the albedo and the outgoing longwave radiation. The analysis of the satellite data enabled direct computation to be made of a heat budget of the earth-atmosphere system. Such computations have been made by several workers (e.g. Raschke et al., 1973; Winston et al., 1979). Some aspects of their work and findings will be reviewed.

An energy balance method in which net heating or cooling of the atmosphere is computed from vertically-integrated radiative heat flux divergence and sensible and latent heat fluxes has been widely used. After the Global Weather Experiment (GWE) in 1979, several workers (e.g., Yeh and Gao, 1979; Nitta, 1983; Luo and Yanai, 1984; Chen et al., 1985; Murakami, 1987) used the energy balance method to compute heat sources and sinks over the Tibetan plateau. Gutman and Schwerdtfeger (1965) and Rao and Erdogan (1989) used the method to compute heat sources and sinks over the Bolivian plateau in South America. The first law of thermodynamics has also been applied to compute the diabatic heating of the atmosphere and locate atmospheric heat sources and sinks from observed atmospheric parameters.

In recent years, a form of the mass continuity equation in isentropic co-ordinates has been integrated by Johnson and his co-workers in the university of Wisconsin (e.g., Johnson, 1980; Wei et al., 1983; Johnson et al., 1985; Schaack et al., 1990; Schaack and Johnson, 1994) to estimate atmospheric heating. They applied the method to locate three-dimensional heat sources and sinks over different parts of the globe in different seasons. Some aspects of these studies will also be reviewed.

Atmospheric heat sources and sinks at the earth's surface are qualitatively identified by meteorological temperature and pressure systems. A 'heat low' or 'a trough of warm low pressure' at the surface, for example, is usually a heat source and associated with penetrative convection, cloudiness and precipitation. On the other hand, a 'cold high' or 'a ridge of cold high pressure' at surface is to be identified as a heat sink where normally air subsides and the process inhibits formation of cloud and rain. Defined in this way, it should be possible to qualitatively verify the accuracy of any computation of heat balance or atmospheric heating over any part of the globe from actual meteorological observations of temperature and pressure and other relevant data. Remote sensing of temperature, moisture and cloudiness by satellites is of great help in this regard.

But, before we take up the study of the heat balance of the earth-atmosphere system, let us first look at the various physical processes known to be involved in the balance.

10.2 Physical Processes Involved in Heat Balance

Physical processes involved in the heat balance of the earth-atmosphere system along with a rough estimate of their contributions to the annual budget can be qualitatively understood as follows: If we take the intensity of the incoming solar radiation at the outer boundary of the atmosphere as 100 units, out of which a total of 30 units is returned to space by way of reflection from the ground and cloud surfaces and backscatter from air molecules, 16 units are absorbed by atmospheric gases such as water vapour and ozone and suspended dust particles, and 3 units are absorbed by clouds, the remaining 51 units are absorbed by the earth's surface. There is also downward longwave radiation amounting to about 98 units

Downward Shortwave Radiation Albedo
Fig. 10.1 Heat balance of the earth-atmosphere system (Reproduced with permission from a report of the National Academy of Sciences panel on Understanding Climate Change', 1975) (Courtesy: National Academies Press, Washington, D.C.)

from the greenhouse gases in the atmosphere, according to an estimate made by London and Sasamori (1971), which, at times, may even exceed the incoming solar radiation. The surface then emits longwave radiation. The net surface emission (excess of upward over downward longwave radiation) is 21 units of which 15 units are absorbed by water vapour and carbon dioxide in the atmosphere, while 6 units escape to space. The other outgoing longwave radiation includes 38 units from water vapour and carbon dioxide and 26 units from clouds. Thus, a total of 70 units of the incoming solar radiation which are absorbed by the earth-atmosphere system are balanced by 70 units of the outgoing longwave radiation.

A schematic in Fig. 10.1, reproduced with permission from a report of the U.S. National Academy of Sciences panel on 'Understanding climate change' (1975), shows these processes.

10.3 Simpson's Computation of Heat Budget

Simpson (1928) computed the annual heat budget of the earth-atmosphere system, making several simplifying assumptions regarding the radiative properties of the earth and its atmosphere. It is not possible to give the full details of his work in this brief survey. Those interested in them may look up his original memoirs (Simpson, 1928 and 1929). Only some salient points of his work are presented here.

After allowing for reflection from the atmosphere, the earth's surface and average cloud amount at different latitudes, Simpson used a value of 0.278 gm-cals per cm2 per minute for the effective incoming solar radiation. He computed the total amount of outgoing radiation with clear and cloudy skies at all latitudes. For the purpose of these computations, he divided the radiation at terrestrial and atmospheric temperatures into the following three categories:

(a) Wavelengths at which water vapour is transparent to radiation, 8/2-111;

(b) Wavelengths in which water vapour amounting to 0.3 mm of precipitable water will completely absorb all the radiation: 51/2-7^, and > 14(;

(c) Wave-lengths in which water vapour absorption is intermediate between (a) and (b): 7-872 ( and 11-14(1.

For a clear sky, Simpson assumed that the radiation of category (a) originated at the earth's surface with a temperature of 280 K, and that of (b) originated in the stratosphere which contains 0.3 mm of precipitable water and has a temperature of 218 K. For (c), he assumed intermediate values between the radiations emitted at the surface and the stratospheric temperatures. For an overcast sky, Simpson used the same procedure but replaced the temperature of the earth's surface by that of the cloud top which he assumes to be 261 K in all latitudes. In his later work, Simpson uses a mean cloud amount of 5/10 for all latitudes and obtains a final figure of 0.271 gm-cals per cm2 per min for the total outgoing radiation from the earth-atmosphere system, a value which is pretty close to that of the net incoming solar radiation. Simpson's results are shown in Fig. 10.2.

In Fig. 10.2 (reproduced from Brunt, 1944, © Cambridge University Press, with permission), Curve I gives the intensity of the net incoming solar radiation and Curve II that of the total outgoing radiation at different latitudes. The difference

Fig. 10.2 Solar and terrestrial radiation

LATITUDE

Fig. 10.3 Simpson's graphical representation of the outgoing terrestrial radiation

Fig. 10.3 Simpson's graphical representation of the outgoing terrestrial radiation

Simpson 1928 Terrestrial Radiation

between the two curves shows that the incoming radiation exceeds the outgoing radiation between the equator and about latitude 35°, but in higher latitudes the outgoing radiation exceeds the incoming radiation. In other words, there is an accumulation of heat in low latitudes which will cause continuous warming of the tropics and depletion in high latitudes which will continuously cool those latitudes. Since this undue heating and cooling are not observed, it follows that a heat balance is reached between the source and the sink through the general circulation of the atmosphere. Curve III in Fig. 10.2 gives the total horizontal transfer of heat across circles of latitude and Curve IV the horizontal heat transfer per cm of circle of latitude.

Fig. 10.3 depicts the method used by Simpson to compute the total outgoing radiation from the earth-atmosphere system, as explained above.

Considering the uncertainties involved in his various assumptions, the results obtained by him were found to be surprisingly accurate and realistic when he (Simpson, 1929), worked out similar data, using monthly means of temperatures.

10.4 Heat Balance from Satellite Radiation Data

The earth-observing satellites which carried scanning radiometers on board in the late sixties and early seventies of the last century enabled direct measurements of incoming and reflected solar radiation and outgoing longwave radiation to be made from a space platform. Raschke et al. (1973) utilized the radiation measurements of the Nimbus 3 satellite flown in 1969 and 1970 to compute the heat budget of the earth-atmosphere system. Their results are shown in Fig. 10.4. Raschke et al. (1973) computed the budget using the relation

where, QN is the net radiation, S0 is the solar constant, a is the albedo of the earth-atmosphere system, and QR is the total outgoing longwave radiation.

Fig. 10.4 Global (G) and hemispherical (N = north, S = south) averages of the radiation budget and its components, computed from Nimbus-3 radiation measurements in 1969 and 1970 (From Raschke et al., 1973, with permission of American Meteorological Society)

Fig. 10.4 Global (G) and hemispherical (N = north, S = south) averages of the radiation budget and its components, computed from Nimbus-3 radiation measurements in 1969 and 1970 (From Raschke et al., 1973, with permission of American Meteorological Society)

Earth Yearly Heat Budget Image

The curves in Fig. 10.4 were constructed from 15-day averages of each of the radiation components given in (10.4.1). The seasonal migration of the heat sources and sinks between the hemispheres is well brought out by them.

Figure 10.5 shows the distribution of the zonally-averaged annual mean net radiation, QN, which is the result of absorbed incoming solar radiation minus outgoing longwave radiation, with latitude, computed from data presented by Winston et al. (1979).

Figure 10.5 confirms that in the annual mean there is a heat source over the equatorial region extending to about 30N and S, and a heat sink over the higher latitudes. Since no undue accumulation or depletion of heat takes place in any part of the earth-atmosphere system, it follows that the atmosphere and the ocean must be so circulating as to achieve a heat budget of the system, i.e., remove excess heat from the source and deliver it to the sink. In this task, the oceanic transfers, though slow, may, in the long term, be considerable. Most of the atmospheric transfers are

Fig. 10.5 Latitudinal distribution of zonally-averaged annual mean net radiation, QN (denoted by S in the Figure), in Wm"2, based on data of Winston et al. (1979). Positive values indicate heat source, negative heat sink

Fig. 10.5 Latitudinal distribution of zonally-averaged annual mean net radiation, QN (denoted by S in the Figure), in Wm"2, based on data of Winston et al. (1979). Positive values indicate heat source, negative heat sink

Satellite Net Radiation

carried out by the general circulation and its perturbations, while the oceanic ones by wind-driven ocean currents.

The seasonal movement of the sun across the equator, however, continually redistributes the computed zonally-averaged net radiation of the earth-atmosphere system, as indicated by Fig. 10.6, which is self-explanatory.

Fig. 10.6 Latitudinal distributions of zonally-averaged mean monthly net radiation over the globe in different months (Based on radiation data of Winston et al., 1979)

Fig. 10.6, which presents the latitudinal distribution of the zonally-averaged heat sources (positive values) and sinks (negative values) for the different months of the year, testfies that the equatorial belt between 10S and 15N remains a heat source almost throughout the year. The same features are also revealed by their geographical distribution presented in Fig. 10.7 (a, b).

In summer (Fig. 10.7a), a heat source with positive values of net radiation appears over a wide belt of the northern hemisphere, extending from about 10S northward to about 60N, while a heat sink appears over the whole southern hemisphere south of 10S. In general, there is a tendency for higher positive values of net radiation to be located over the continents of Asia, Africa, and North America than over the neighboring oceans. High positive values also appear over the warmer parts of the northern oceans.

In winter (Fig. 10.7b), the situation is reversed. The northern hemisphere, north of about 15N, now appears as a heat sink. Positive values of net radiation appear over the whole latitude belt south of this latitude with maxima located over the

Fig. 10.7 Geographical distribution of net radiation (Wm"2) over the globe during the northern hemisphere: (a) Summer (June-August); (b) Winter (December-February) Areas with negative values are shaded (After Winston et al., 1979)

subtropical belt of the southern hemisphere, especially over the continents of South America, South Africa and Australia and some warmer parts of the southern oceans. Heat sinks appear over the vast desert areas of Africa and Asia and also over ocean areas dominated by cold ocean currents in both the seasons.

10.5 Heat Sources and Sinks from the Energy Balance Equation

Heat sources and sinks have been estimated from values of net radiation and sensible and evaporative heat fluxes, using a relation of the form

where

R^ is the net radiation at the outer limit of the atmosphere,

R0 is the net radiation at the earth's surface, and

Qs and Qe are the sensible and evaporative heat fluxes respectively.

The relation (10.5.1) has been used to compute heat sources and sinks over different regions of the globe, notably the Tibetan plateau during the northern summer by several workers (e.g., Yeh and Gao,1979; Nitta,1983; Luo and Yanai, 1983,1984; and Chen et al., 1985) and the Bolivian plateau in South America during January by Rao and Erdogan (1989) and others.These computations were made using conventional meteorological data of net radiation, temperature, wind and moisture content and surface vegetation over the respective regions, and, in some cases, satellite-observed net radiation. We give here a brief description of the work of the above-mentioned workers in respect of the Tibetan plateau.

Yeh and Gao (1979) in their book on the meteorology of the Tibetan plateau summarizes the results of early Chinese research on the heat balance of the western and the eastern parts of the plateau as well as the whole plateau. They tabulated the monthly mean values of the sensible and latent heat fluxes as well as the precipitation, using the long-term surface records of the available meteorological stations at a mean height of about 4 km, the line of demarcation between the two parts being about 85E. From the tabulated data, they estimated the monthly mean values of net atmospheric heat source over the two parts of the plateau as well as the plateau as a whole. Their results are shown in Table 10.1.

The values of the monthly mean sensible and latent heat fluxes and the net heat source over the two parts of the plateau, as computed by these workers, are shown in Fig. 10.8.

From Fig. 10.8, one may immediately note an extremely large sensible heat flux over the arid western part of the plateau (where it reaches a maximum value of about 450 units in June), compared to the eastern part where the values are much lower and a maximum of about 250 units is reached in May, a month earlier than over the western part. The distribution of latent heat flux between the two parts, however, varies in the reverse direction, being much larger over the eastern than over the

Table 10.1 The net atmospheric heat source (Wm-2) over the Tibetan plateau (after Yeh and Gao, 1979).

Month

Eastern Plateau -72 -48 -8 38 73 89 92 67 40 -17 -53 -78 10 Western Plateau -71 -31 59 106 134 138 120 90 51 6 -55 -76 39 Weighted Mean -72 -42 25 60 94 109 101 74 44 -10 -54 -77 21

Fig. 10.8 Ten-year (1961-1970) means for sensible heat flux at the surface(Qsens denoting Qs), latent heat of precipitation(Qlat denoting Qe) and net atmospheric heat source (Q), over the western(W) and eastern(E) Tibetan plateau (After Yeh and Gao, 1979)

2 3 4 5 6 7 8 9 10 11 12 MONTH

western part. Further, the latent heat flux over the eastern part reaches its maximum value in July, a month earlier than over the western part. It is also noteworthy that a feeble maximum appears in latent heat flux curve over the western part of the plateau in March, while no such maximum appears then over the eastern part. Because of the predominance of sensible heat flux over latent heat flux, the western part of the plateau contributes more to the net heat source over the plateau than the eastern part, as shown by the distribution of net atmospheric heat source (Q) in Fig. 10.8.

There was renewed interest in the study of the heat budget of the Tibetan plateau during the Global Weather Experiment (GWE) in 1979 when there was an improved network of surface and upper-air observing stations over the plateau. Several studies were conducted using the special data that became available during this experiment. For details of data used by these studies, the original papers should be consulted. Here we give only a brief description of the method that was used by Nitta (1983) and Luo and Yanai (1983, 1984) and also by Chen et al. (1985) and some of the results reported by them. In addition to heat budget, they also computed the moisture budget, using the following expressions for Q1 which they called the apparent heat source, and Q2 the moisture sink ps ps

pt pt ps

pt where ps and pT are pressures at the surface and top of the atmosphere respectively, Qr stands for radiative heating, LP is the latent heat released to the atmosphere by precipitation, SH is sensible heat exchange with the ground and LE is the heat used for evaporation of water from the lower boundary.

If we denote the left-hand sides of (10.5.2) and (10.5.3) by < Q1 > and < Q2 > respectively and assume that ps

pt where R» and R0 are the net radiation at the top of the atmosphere and the earth's surface respectively and both values are treated as positive if directed downward, (10.5.2) and (10.5.3) may finally be written as

< Q1 > = (R» -R0)+LP + SH = RC + LP + SH (10.5.5)

where RC in (10.5.5) stands for (R» - R0) and signifies radiative cooling.

While Nitta (1983) and Luo and Yanai (1983, 1984) evaluated Q1 and Q2 at individual pressure surfaces and then carried out the vertical integration, Chen et al.

(1985) adopted a slightly different procedure and evaluated the apparent heat source and moisture sink over the plateau directly from observations. R^ was evaluated from Nimbus-7 radiation data and R0 was calculated from an empirical relationship which took into consideration, amongst others, the intensities of the incoming solar radiation and the outgoing longwave radiation at the ground, the surface albedo, the declination of the sun, the latitude of the place, the mean cloud amount and water vapour pressure in the atmosphere and the state of vegetation at the surface.

The sensible heat flux, SH, was calculated from the standard relation

where p is air density, cp is the specific heat of air at constant pressure, CD is drag co-efficient, V0 is the mean wind speed at about 10 m above the ground, Tg is the ground temperature and Ta is the air temperature immediately above the ground. The latent heat released into the atmosphere, LP, is calculated easily from precipitation data. LE is difficult to calculate over the plateau because of the paucity of evaporation data and was obtained as a residual in the heat balance equation.

Table 10.2 presents the mean values of the apparent heat source and moisture sink and their components (SH, LP, RC, LE) over the whole plateau and its eastern and the western parts during the period June-August 1979, as computed by Chen et al. (1985), along with those of Yeh and Gao (1979), for comparison. The values computed by Nitta (1983) for the eastern part of the plateau are also included. The values computed by Luo and Yanai (1984) for the eastern and the western parts of the plateau were available for the month of June only and are, therefore, not included in the Table.

It is clear from Table 10.2 that a net heat source resides over the Tibetan plateau during the northern summer. However, the extent of atmospheric heating varies widely amongst the different computations, being minimum in CRF. Strong radiative cooling is found over the plateau by all the computations. It is also found that while sensible heating dominates over precipitation heating over the arid western part, precipitation heating dominates over sensible heating over the more humid eastern part.

Table 10.2 Mean values of the atmospheric heat source and its components, Wm-2, over Tibet during June-August 1979, computed by Chen, Reiter and Feng (CRF), 1985; Yeh and Gao (Y&G), 1979; and Nitta, 1983. (After Chen et al., 1985)

Whole plateau Eastern part Western part

Table 10.2 Mean values of the atmospheric heat source and its components, Wm-2, over Tibet during June-August 1979, computed by Chen, Reiter and Feng (CRF), 1985; Yeh and Gao (Y&G), 1979; and Nitta, 1983. (After Chen et al., 1985)

Whole plateau Eastern part Western part

CRF

Y&G

CRF

Y&G

Nitta

CRF

Y&G

< Q1 >

64

94

77

82

120

46

116

< Q2 >

19

31

25

1

SH

59

118

50

82

(105)

70

189

LP

65

73

87

97

90

35

24

RC

-60

-96

-60

-97

-75

-59

-97

LE

47

56

65

34

10.6 Computation of Atmospheric Heating from Mass Continuity Equation

Johnson et al. (1987) reviewed the method to estimate three-dimensional atmospheric heating over different parts of the globe by integrating the time-averaged mass continuity equation in isentropic co-ordinates in the following form d(pJe)/dte + Ve • (pJU) + d(J)/d9 = 0 (10.6.1)

where p is density, 9 is potential temperature, z is height, J9 is the transformation Jacobian |dz/d9| (from z to 9 surface), U is velocity, t is time and the overbar denotes a time average.

The atmospheric mass within an isentropic layer is determined by the difference in pressure between the lower and the upper isentropic levels, as given by the hydrostatic equation p Je = -(1/g) dp/d9 (10.6.2)

where p is pressure and g is acceleration due to gravity.

The diabatic mass flux through an isentropic surface 9 is estimated by vertical integration of (10.6.1)

9t p Je 9 = j[dJJ)/die + Ve • (pJeU)] d9 (10.6.3)

where the diabatic mass flux is assumed to vanish at the isentropic surface (9T) at the top (T) of the atmosphere.

This form of the continuity equation gives the relation between the diabatic mass flux at an isentropic surface and the mass tendency and mass divergence within the overlying atmosphere.

The heating rate, 9, obtained from (10.6.3), is equivalent to the thermodynamic relation

where Q is the rate of heating and the denominator within the second bracket on the right-hand side is the Exner function with poo as standard pressure at 1000mb surface.

The heating rate calculated from (10.6.3) is open to several sources of error, due to inaccuracies likely in the specification of the vertical profile of the mass tendency or the horizontal mass divergence. A systematic mass-weighted adjustment is therefore applied to the computed diabatic mass flux based on the integral constraint that the sum of the vertically-integrated mass tendency and mass divergence must reduce to the diabatic mass flux at the earth's surface. The following is a brief description of the adjustment procedure.

The vertical integral of the isentropic mass continuity equation (10.6.3) when integrated from surface to top of the layer may be written as

(pJee)|0S = y [5(pJ0)/5t0 + V0 • (p J0 U)] d0 (10.6.5)

0s where 0T and 0S are the potential temperatures at the top of the layer and the earth's surface respectively. In (10.6.5), the diabatic mass flux at the top of the layer is assumed to vanish.

Due to inaccuracies from various sources in the computation of the right-hand side of (10.6.5), the computed diabatic mass flux at the earth's surface using (10.6.5) will differ from that estimated from the actual variation of potential temperature at the surface which may be expressed as

where X and ^ are the longitude and latitude of the place respectively.

The true value of the diabatic mass flux at the earth's surface is, therefore, assumed to be given by pj0 0 10S = p J0 0S(X, t) = p J0 (d0s/dt0 + Us • V0 0s) (10.6.7)

The difference between (10.6.5) and (10.6.7) then represents the vertically-integrated systematic error, 5, given by

If e represents error per unit mass of the atmospheric column, it is given by

The adjusted diabatic mass flux at an isentropic surface (0) is then given by

(p 10 0) = y [d(p j0)/dt0 + V0 • (p J0 U) - p J0 e] d0 (10.6.10)

In this method, the integrated error is distributed through the vertical column in proportion to the mass within an isentropic layer.

Johnson and his co-workers used the adjusted diabatic mass flux to estimate mass-weighted vertically-averaged heating rates over the whole globe over different periods of time. They computed the distributions of atmospheric heating by using the Global Weather Experiment (GWE) level Illb data set prepared by the European Center for Medium-Range Weather Forecast (ECMWF) for the four seasons of 1979. Their results reveal several interesting details regarding the locations of heat sources and sinks over different parts of the globe in different seasons, as summarized below.

In January, with the sun in the southern hemisphere, the principal heat sources appear over land areas south of the equator, with maximum heating over the continents of South America, Southern Africa and Australia, and over warm equatorial oceans, not directly affected by cold ocean currents. The heat source over the Australian region appears to be a southward extension of an extensive and intense heat source that resides over the maritime continent and ocean areas lying to the northeast of Australia and extending southeastward deep into southwestern Pacific along the South Pacific Convergence Zone (SPCZ). Principal heat sinks appear over the southern oceans dominated by cold ocean currents. In general, the land areas to the north of the equator appear as heat sinks, except the elevated Tibetan plateau where a weak heat source appears to exist. By contrast, large parts of the northern oceans lying to the east of the continents of Asia and North America appear as prominent heat sources in January.

In April, with maximum solar heating now being over the equatorial zone, there is a general northward movement of the heat sources and sinks from their January locations. The whole equatorial belt now appears as a heat source. A continuous and well-marked heat source appears all along the equatorial Pacific which was earlier interrupted by cold ocean currents over the eastern Pacific. The intense heat source over the maritime continent and adjoining southwestern Pacific to the northeast of Australia with extension along the SPCZ appears to persist. The heat source over the Tibetan plateau appears to have intensified.

In July, with the sun in the northern hemisphere, heat sources and sinks appear to have moved further northward. In the northern hemisphere, all the continents appear as heat sources while adjoining ocean areas to the south appear as heat sinks. The heat source over the Tibetan plateau appears to have further intensified to a value exceeding 3 K per day. It now appears to be directly connected with the heat source over the maritime continent and the SPCZ which extends into the southwestern Pacific. The equatorial heat source along the intertropical convergence zone (ITCZ) in the Pacific appears to be interrupted by cold ocean currents in the mid-Pacific. In general, most of the land and ocean areas south of the equator appear as heat sinks.

The October distribution largely resembles that of April, except that the heat source maximum over the Tibetan plateau which was conspicuous in July has considerably weakened and shows sign of retreat southeastward, thereby strengthening the heat source over equatorial western Pacific and the SPCZ.

Besides the vertically-averaged estimates of heating, they also worked out layer-averaged heating rates for the isobaric layers, surface to 800 mb, 800-600 mb, 600-400 mb, and 400-200 mb. The heating rates in isobaric layers were obtained by interpolation from isentropic to isobaric surfaces.

Part II

Dynamics of the Earth's Atmosphere - The

General Circulation

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  • medhane
    What is LATITUDINAL HEAT BALANCE OF THE EARTH?
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    How much shortwave radiation is absorbed by the Earth's surface?
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  • Rudigar
    How the atmosphere is heat and the processes involved?
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