# Relationship between insolation curve and air temperature

### 7(l) Daily and Annual Cycles of Temperature

Conduction is when heat is conducted from the ground to the air that is in direct The diagram below illustrates how the change in the curvature of the Earth has a vital . Note that the lowest temperature is not at midnight but just after sunrise. The air temperature at a place is determined by the exchange of radiant energy increases after sunrise but lags somewhat behind the insolation curve. The following three graphs show hypothetical average curves of insolation, net radiation, and air temperature for a typical land based location at 45° of latitude.

The mean daily temperaure is defined as the average of the maximum and minimum daily values. The monthly mean temperature for each station is determined by averaging the daily means for each day in the calendar month.

The annual mean temperature represents the average of the 12 monthly mean. The difference between the means of the warmest and coldest months is the annual temperature range.

Daily temperature pattern is decided by daily net radiation pattern. Graph a shows daily insolation.

There are several features in this figure. At the equinox middle curveinsolation begins at about sunrise 6 amrises to a peak value at noonand declines to zero at sunset 6 pm. At the June solstice, insolation begins about two hours earlier 4 am and ends about two hours later 8 pm.

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At the Decemeber solstice, insolation begins about two hours later than the equinox and ends two hours earlier. Graph b shows net radiation for the surface. Net radiation is the difference between incoming radiation and outgoing radiation.

If the incoming radiation is greater than outgoing radiation, then net radiation is positive or surplus, otherwise, net radiation is negative or deficit.

Compare graph b with awe can see it is generally similar in shape. Latent heat transfer - Energy is required to evaporate water into a vapour. Therefore, the energy that was required to evaporate the water is stored within the vapour as latent heat. The vapour then rises into the atmosphere through convection, or through forced rise along fronts or up mountains or by turbulence.

## Daily and Annual Cycles of Air Temperature

On condensation the latent heat is released into the atmosphere as sensible heat, which warms the atmosphere. Once in the atmosphere gases and liquids absorb the long-wave radiation. Therefore, does this mean that the polar regions are getting cooler and the tropical regions warmer? The answer is no! Trade winds - These transfer large amounts of heat from the tropics to the poles. Storms - These tropical cyclones transfer large amounts of heat energy from the tropics where they develop to the subtropics and temperate zones.

The map below illustrates the global distribution of insolation reaching the earth's surface. There are many reasons why insolation reaching the earth's surface is not evenly distributed across the planet.

Tempertue inversion in hindi - Normal lapse rate of temperature - Normal lapse rate geography

The following are the main reasons: Units in Figure 7l-2 are the same as the insolation graph above. The net radiation graph indicates that there is a surplus of radiation during most of the day and a deficit throughout the night.

The deficit begins just before sunset when emitted longwave radiation from the Earth's surface exceeds solar insolation and longwave radiation from the atmosphere. The relative placement of the temperature profiles for the various dates correlates to the amount of net radiation available for daily surface absorption and heat generation.

The more energy available, the higher up the Y-axis the profile is on the graph. September equinox is warmer than the March equinox because of the heating that occurred in the previous summer months.

For all dates, minimum temperature occurs at sunrise. Temperature drops throughout the night because of two processes.

### Daily and Annual Cycles of Air Temperature

First, the Earth's radiation balance at the surface becomes negative after sunset. Thus, the surface of the Earth stops heating up as solar radiation is not being absorbed. Secondly, conduction and convection transport heat energy up into the atmosphere and the warm air that was at the surface is replaced by cooler air from above because of atmospheric mixing.

Temperature begins rising as soon as the net radiation budget of the surface becomes positive. Temperature continues to rise from sunrise until sometime after solar noon. After this time, mixing of the Earth's surface by convection causes the surface to cool despite the positive addition of radiation and heat energy.

Annual Cycle of Air Temperature As the Earth revolves around the Sun, locations on the surface may under go seasonal changes in air temperature because of annual variations in the intensity of net radiation. Variations in net radiation are primarily controlled by changes in the intensity and duration of received solar insolation which are driven by variations in daylength and angle of incidence.

The discussion below examines how changes in net radiation can effect mean monthly temperatures for the following five locations: Monthly variations in net radiation and average monthly temperature for Manaus, Brazil.

At Manaus, values of monthly net radiation average about Watts per square meter.