ABSTRACT - DRUM - University of Maryland

there is, as expected, a general symmetry about the overshoot. Fig. 3.2c shows the
0.63-µm data, which is mainly reflected solar radiation. The amount reflected
increases on the sun side of the overshoot and suddenly decreases after the overshoot.
This pronounced decrease in signal on the side of the overshoot opposite from the sun
is the shadow that the overshoot has cast on the surrounding cloud. Note that the
enhanced radiance on the sun side has been attributed by Van Hees and Lelieveld
[2000] to the change of the slope of reflecting surface. Structured cloud tops change
the slope of illuminated cloud top surface, so they make more radiation to be reflected
upward. 3.75-µm channel data are also used to identify the same phenomena.
Due to the ethereal nature of clouds and relatively coarse resolution of the VIRS
data, it is impossible to define the exact position of the end of the shadow. In this study,
the following recipe was used to determine the end of the shadow. Point A in Fig. 3.2c
is the location of the minimum value of 0.63-µm radiance. The shadow end is
assumed midway between this pixel and the adjacent pixel (denoted as B). Based on
the length of the shadow and the solar zenith angle, the overshoot height dH is
calculated.
3.4 The overshooting height calculation and analysis
3.4.1 The overshooting height calculation
We take TRMM data for an entire month and isolate those scenes that include
10.8-µm channel brightness temperatures below 200 K, which are typical anvil
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