A standard test for AGCMs including their physical parametrizations: I: The proposal

To assist model intercomparison and development of a set of eight numerical experiments is proposed as a test-bed for the interaction of dynamics and physical parameterizations in atmospheric GCMs. The framework for the experiments is that of an aqua-planet and the prescribed sea-surface temperatures (SSTs) are highly idealized.     

The 183-WSL fast rain rate retrieval algorithm: Part I: Retrieval design

The Water vapour Strong Lines at 183 GHz (183-WSL) fast retrieval method retrieves rain rates and classifies precipitation types for applications in nowcasting and weather monitoring. The retrieval scheme consists of two fast algorithms, over land and over ocean, that use the water vapour absorption lines at 183.31 GHz corresponding to the channels 3 (183.31 ± 1 GHz), 4 (183.31 ± 3 GHz) and 5 (183.31 ± 7 GHz) of the Advanced Microwave Sounding Unit module B (AMSU-B) and of the Microwave Humidity Sounder (MHS) flying on NOAA-15-18 and Metop-A satellite series, respectively.The method retrieves rain rates by exploiting the extinction of radiation due to rain drops following four subsequent steps. After ingesting the satellite data stream, the window channels at 89 and 150 GHz are used to compute scattering-based thresholds and the 183-WSLW module for rainfall area discrimination and precipitation type classification as stratiform or convective on the basis of the thresholds calculated for land/mixed and sea surfaces. The thresholds are based on the brightness temperature difference Δ_win = T_B89 ? T_B150 and are different over land (L) and over sea (S): cloud droplets and water vapour (Δ_win < 3 K L; Δ_win < 0 K S), stratiform rain (3 K < Δ_win < 10 K L; 0 K < Δ_win < 10 K S), and convective rain (Δ_win > 10 K L and S). The thresholds, initially empirically derived from observations, are corroborated by the simulations of the RTTOV radiative transfer model applied to 20000 ECMWF atmospheric profiles at midlatitudes and the use of data from the Nimrod radar network. A snow cover mask and a digital elevation model are used to eliminate false rain area attribution, especially over elevated terrain. A probability of detection logistic function is also applied in the transition region from no-rain to rain adjacent to the clouds to ensure continuity of the rainfall field. Finally, the last step is dedicated to the rain rate retrieval with the modules 183-WSLS (stratiform) and 183WSLC (convective), and the module 183-WSL for total rainfall intensity derivation.A comparison with rainfall retrievals from the Goddard Profiling (GPROF) TRMM 2A12 algorithm is done with good results on a stratiform and hurricane case studies. A comparison is also conducted with the MSG-based Precipitation Index (PI) and the Scattering Index (SI) for a convective-stratiform event showing good agreement with the 183-WSLC retrieval. A complete validation of the product is the subject of Part II of the paper.     

Climate change: High-latitude regions

The distinctive physical setting of high-latitude regions results not only in enhanced change in mean surface temperature for a given perturbation of planetary heat balance, but an enhanced regional and seasonal environmental response due to non-uniformity in poleward heat flux, and to the energy relationships of phase change and albedo change connected with ice and snow cover. The environmental response of the Arctic is characteristically different from that of the Antarctic because of differences in planetary geography and energy circulation. Ecosystems that have adapted to the low natural energy flows of high latitudes are relatively more sensitive to a given change in magnitude and timing of available energy, and to changes in physical and geochemical conditions, than most of those in lower latitudes. These natural sensitivities have a profound influence on human activities in polar areas. Policies to adapt to, or where possible to benefit from the environmental changes that will be brought about by climate change in high latitudes will have to be adapted to the distinctive environmental responses of polar areas. Careful research to understand the environmental response to climate change is essential as arctic and antarctic regions assume a greater importance in world affairs, and as the arctic regions in particular are the subject of increasing policy attention on strategic, resource development, socioeconomic and environmental protection grounds.