A physical model to determine snowfall over land by microwave radiometry

Abstract

Abstract-Falling snow is an important component of global precipitation in extratropical regions. This paper describes the methodology and results of physically based retrievals of snow falling over land surfaces. Because microwave brightness temperatures emitted by snow-covered surfaces are highly variable, precipitating snow above such surfaces is difficult to observe using window channels that occur at low frequencies ( 100 GHz). Furthermore, at frequencies 37 GHz, sensitivity to liquid hydrometeors is dominant. These problems are mitigated at high frequencies ( 100 GHz) where water vapor screens the surface emission, and sensitivity to frozen hydrometeors is significant. However, the scattering effect of snowfall in the atmosphere at those higher frequencies is also impacted by water vapor in the upper atmosphere. The theory of scattering by randomly oriented dry snow particles at high microwave frequencies appears to be better described by regarding snow as a concatenation of "equivalent" ice spheres rather than as a sphere with the effective dielectric constant of an air-ice mixture. An equivalent sphere snow scattering model was validated against high-frequency attenuation measurements. Satellite-based high-frequency observations from an Advanced Microwave Sounding Unit (AMSU-B) instrument during the March 5-6, 2001 New England blizzard were used to retrieve snowfall over land. Vertical distributions of snow, temperature, and relative humidity profiles were derived from the Mesoscale Model (MM5) cloud model. Those data were applied and modified in a radiative transfer model that derived brightness temperatures consistent with the AMSU-B observations. The retrieved snowfall distribution was validated with radar reflectivity measurements obtained from a ground-based radar network.

Sensitivity analysis and implications for surface processes from a hydrological modelling approach in the Gunt catchment, high Pamir Mountains

“…Detection problems of falling snow related to already existent snow cover have been pointed out by, for example, Yin (2004). Even though microwave imagers as used for the TRMM3B42 product can recognise snowfall, the quality relies on the discrimination between frozen precipitation and antecedent snow cover (Skofronick-Jackson and Weinman, 2004). Other authors have reported an underestimation of precipitation in cases of intense snowfall in the Himalayas (Kamal-Heikman et al, 2007).…”

“…In particular, we find the three data sets to have the following issues. TRMM3B42 V7 most likely suffers from reported issues on snowfall determination (Yin, 2004;Kamal-Heikman et al, 2007;Skofronick-Jackson and Weinman, 2004;Prigent, 2010) that result in, for example, low snow stocks that lead to the underestimation of the hydrograph in 2002 and 2004. The fact that TRMM detects precipitation when there must be at least partial snow cover, and the determination of falling snow should hence be problematic, leads us to wonder what TRMM really records and with what confidence.…”

Detecting snowfall over land by satellite high‐frequency microwave observations: The lack of scattering signature and a statistical approach

“…However, because CPR does not scan, it only measures a 1.5 km-wide strip on the Earth surface by each satellite pass, which largely limits its utility for weather monitoring and climate data collection. Passive satellite sensors such as high-frequency (>80 GHz) microwave radiometers have also been used in detecting snowfall events [Liu and Curry, 1997;Chen and Staelin, 2003;Kongoli et al, 2003;Ferraro et al, 2005;Skofronick-Jackson et al, 2004;Noh et al, 2006Noh et al, , 2009. While most of these studies targeted moderate to heavy snowfall events under unfrozen or nonsnow-covered surfaces, the encouraging results from these studies offered a viable alternative to high-sensitivity space-borne radar for snowfall detection and retrieval.…”

A Simple Model of the Millimeter-Wave Scattering Parameters of Randomly Oriented Aggregates of Finite Cylindrical Ice Hydrometeors

“…Emission from partially snow-covered land surface is obscured by water vapor absorption in that band. Moreover the chan-nels operating at frequencies greater than 85 GHz are more sensitive to scattering by snow so that it is possible to monitor snowfall within the atmosphere (Weng et al 2003;Skofronick-Jackson et al 2004;. The forthcoming Global Precipitation Mission (GPM) will include millimeter-wave radiometers to measure snowfall.…”