Cloud Statistics from Calipso Lidar Data for the ... - espace-tum.de

Chapter 4. Case studies 37
4.2 Multilayered cloud scene
14
12
Layer plot from 01 Jan 2007 09:17:36 until 01 Jan 2007 09:18:06 (UTC)
333m layer product boundary
Lidar Surface
DEM Surface
Cloud layers
Cloud layers 5km
10
Height [km]
8
6
4
2
0
09:17:36 09:17:41 09:17:46 09:17:51 09:17:56 09:18:01 09:18:06
UTC Time [hh:mm:ss]
(a)
Top height occurence in current selection
14
Height with binned 30m layers [km]
12
10
8
6
4
2
(b)
0
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
Probability normalized
(c)
Figure 13: A typical multi-layer situation above the South Pacific Ocean with no
surface return (b) and with at least three different distinct layers (a) at 11.8 km, 5.6
km and 4.1 km height (c). The dominance and vertical extent of the cirrus cloud is
evident whereas the optical depth is quite low.
The cloud scene described by Figure 13 is a typical representation of a vertically scattered
multi layered sky cover combined with a relatively dense cirrus ranging over more than
3 km vertical extent from the 5 km product. The scene was captured at nighttime above
the South Pacific. If a threshold of τ ≤ 0.5 had been chosen for the merging process, the
overlying cirrus cloud would not only have dominated the whole scene, but it would have
covered the entire 200 km completely. The fact that a cirrus cloud at that height with
an optical depth of ≥0.5 and more than 3 km vertical extent is present and CALIOP
still can detect two additional separated cloud layers, could be quite challenging for
MERLIN. However, looking at the horizontal averaging parameter confirms that the
cloud was detected at the maximum averaging step of 80 km and therefore is optically
very thin. Nevertheless the entire scene is assumed to be totally cloud covered.