Typical Behavior of Atmospheric and Soil Temperature
17
Time (hrs)
FIGURE 2.2. Hourly air temperature (points) on a clear fall day at Hanford, WA.
The curve is used to interpolate daily maximum and minimum temperatures to
obtain hourly estimates.
motion, or transport of parcels of hot or cold air over relatively long vertical distances, rather than by molecular motion. Within the first few meters
of the atmosphere of the earth, the vertical distance over which eddies
can transport heat is directly proportional to their height above the soil
surface. The larger the transport distance, the more effective eddies are
in transporting heat, so the air becomes increasingly well mixed as one
moves away from the surface of the earth. This mixing evens out the temperature differences between layers. This is the reason for the shape of
the air temperature profiles in Fig. 2.1. They are steep close to the surface
because heat is transported only short distances by the small eddies. Farther from the surface the eddies are larger, so the change of temperature
with height (temperature gradient) becomes much smaller.
In addition to the diurnal temperature cycle shown in Fig. 2.2, there
also exists an annual cycle with a characteristic shape. The annual cycle
of mean temperature shown in Fig. 2.3 is typical of high latitudes which
have a distinct seasonal pattern fiom variation in solar radiation over the
year. Note that the difference between maximum and minimum in Fig. 2.3
is similar to the difference between maximum and minimum of the diurnal
cycle in Fig. 2.2. Also note that the time of maximum temperature (around
day 200) significantly lags the time of maximum solar input (June 2 1 ; day
172). The explanation for this lag is the same as for the diurnal cycle.
17
Time (hrs)
FIGURE 2.2. Hourly air temperature (points) on a clear fall day at Hanford, WA.
The curve is used to interpolate daily maximum and minimum temperatures to
obtain hourly estimates.
motion, or transport of parcels of hot or cold air over relatively long vertical distances, rather than by molecular motion. Within the first few meters
of the atmosphere of the earth, the vertical distance over which eddies
can transport heat is directly proportional to their height above the soil
surface. The larger the transport distance, the more effective eddies are
in transporting heat, so the air becomes increasingly well mixed as one
moves away from the surface of the earth. This mixing evens out the temperature differences between layers. This is the reason for the shape of
the air temperature profiles in Fig. 2.1. They are steep close to the surface
because heat is transported only short distances by the small eddies. Farther from the surface the eddies are larger, so the change of temperature
with height (temperature gradient) becomes much smaller.
In addition to the diurnal temperature cycle shown in Fig. 2.2, there
also exists an annual cycle with a characteristic shape. The annual cycle
of mean temperature shown in Fig. 2.3 is typical of high latitudes which
have a distinct seasonal pattern fiom variation in solar radiation over the
year. Note that the difference between maximum and minimum in Fig. 2.3
is similar to the difference between maximum and minimum of the diurnal
cycle in Fig. 2.2. Also note that the time of maximum temperature (around
day 200) significantly lags the time of maximum solar input (June 2 1 ; day
172). The explanation for this lag is the same as for the diurnal cycle.