A new retrieval method to detect steep temperature gradients between the co
nvective overshoots of cumulonimbus clouds and the surrounding cirrus has b
een applied to determine gradients and their orientation in the image plane
of infrared data of the advanced very high resolution radiometer (AVHRR).
These orientations are used to derive cloud elevations which are brightened
by the Sun or are in shadow, which strongly affects the visible signal. Th
e impact of temperature gradients on the visible radiances is illustrated b
y two examples that indicate deep convective overshoots. Both examples show
that the illuminated side of the overshoots can exceed the cloud top refle
ctivity by 50%, while the shadows account for < 50% of the cloud top reflec
tance. The shadows usually extend several pixels beyond the base of the ove
rshoots. Here we show that statistical analyses of cloud optical depth are
affected by the cloud top structure, based on 1 month of high-resolution AV
HRR satellite data. The contribution of shadow side pixels with steep tempe
rature gradients (greater than or equal to 16 K) can exceed 30% for small o
ptical depths (< 3). The contribution of illuminated sides of cloud top str
uctures and cloud sides with steep temperature gradients can exceed 70% for
large optical depths (> 32).