Remote sensing of cloud liquid water during ICE'89

The cloud liquid water path, LWP, over the North Sea during the International Cirrus Experiment 1989 (ICE'89) is derived from measurements of the microwave radiometer SSM/I on board.of the polar orbiting satellite DMSP and from measurements of a ground-based 33-GHz-radiometer operating on board of the German research vessel 'Poseldon'. Comparisons of maps of LWP compiled from the SSM/I data with time series computed from the ground-based system show no significant bias and agree within the range of uncertainty caused by the different sampling characteristics of the observing systems. Using a combination of SSM/I data and almost simultaneously recorded METEOSAT-IR data offers the possibility to identify different cloud types, e.g. to seperate cirrus clouds and cirrus with underlying water clouds. Both types may have the same IR-brightness temperature but different microwave brightness temperature because ice clouds have a negligible influence on the microwave radiances

The simulation of L-band microwave emission of frozen soil during the thawing period with the Community Microwave Emission Model (CMEM)

One-third of the Earth's land surface experiences seasonal freezing and thawing. Freezing-thawing transitions strongly impact land-atmosphere interactions and, thus, also the lower atmosphere above such areas. Observations of two L-band satellites, the Soil Moisture Active Passive (SMAP) and Soil Moisture and Ocean Salinity (SMOS) missions, provide flags that characterize surfaces as either frozen or not frozen. However, both state transitions-freezing and thawing (FT)-are continuous and complex processes in space and time. Especially in the L-band, which has penetration depths of up to tens of centimeters, the brightness temperature (TB) may be generated by a vertically-mixed profile of different FT states, which cannot be described by the current version of the Community Microwave Emission Model (CMEM). To model such complex state transitions, we extended CMEM in Fresnel mode with an FT component by allowing for (1) a varying fraction of an open water surface on top of the soil, and (2) by implementing a temporal FT phase transition delay based on the difference between the soil surface temperature and the soil temperature at 2.5 cm depth. The extended CMEM (CMEM-FT) can capture the TB progression from a completely frozen to a thawed state of the contributing layer as observed by the L-band microwave radiometer ELBARA-III installed at the Maqu station at the northeastern margin of the Tibetan Plateau. The extended model improves the correlation between the observations and CMEM simulations from 0.53/0.45 to 0.85/0.85 and its root-mean-square-error from 32/25 K to 20/15 K for H/V-polarization during thawing conditions. Yet, CMEM-FT does still not simulate the freezing transition sufficiently.</p