Most atmospheric motions of different spatial scales and precipitation are closely related to phase transitions in clouds. The continuously increasing resolution of large-scale and mesoscale atmospheric models makes it feasible to treat the evolution of individual clouds. The explicit treatment of clouds requires the simulation of cloud microphysics. Two main approaches describing cloud microphysical properties and processes have been developed in the past four and a half decades: bulk microphysics parameterization and spectral (bin) microphysics (SBM). The development and utilization of both represent an important step forward in cloud modeling. This study presents a detailed survey of the physical basis and the applications of both bulk microphysics parameterization and SBM. The results obtained from simulations of a wide range of atmospheric phenomena, from tropical cyclones through Arctic clouds using these two approaches are compared. Advantages and disadvantages, as well as lines of future development for these methods are discussed.

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[1] The Active Red Sea Trough (ARST) is an infrequent weather phenomenon that is associated with extreme precipitation, flash floods, and severe societal impacts in the Middle East (ME). Using reanalysis (ERA-Interim) and observational precipitation (Aphrodite and stations) data, we investigate its underlying dynamics, geographical extent, and seasonality. Twelve ARST events affecting the Levant have the same dynamical characteristics as those associated with a major flood in Jeddah (Saudi Arabia) on 25 November 2009. Hence, the Jeddah flooding was caused by an ARST, which implies that ARSTs can affect a much larger part of the ME than previously assumed. We present an ARST concept involving six dynamical factors: (1) a low-level trough; the Red Sea Trough (RST), (2) an anticyclone over the Arabian Peninsula; the Arabian Anticyclone (AA), (3) a transient midlatitude upper trough, (4) an intensified subtropical jet stream, (5) moisture transport pathways, and (6) strong ascent resulting from tropospheric instability and the synoptic-scale dynamical forcing. We explain the ARST as the interaction of a persistent stationary wave in the tropical easterlies (i.e., the RST) with a superimposed amplifying Rossby wave, resulting in northward propagating moist air masses over the Red Sea. Our findings emphasize the relevance of the AA, causing moisture transport from the Arabian and Red Seas. The particular topography in the Red Sea region and associated low-level circulation makes the ARST unique among tropical-extratropical interactions. The ARST seasonality is explained by the large-scale circulation and in particular the seasonal cycle of the semipermanent quasi-stationary RST and AA.

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Investigation of the role of the east Atlantic-west Russia (EA-WR) teleconnection pattern in determining the variability of the monthly mean Mediterranean area precipitation is performed. Space correlations between the mean monthly precipitation and the EA-WR index during 1950-2000 have been calculated. The EA-WR/precipitation correlations are statistically significant over the eastern Atlantic and southeastern Mediterranean regions. Two pairs of 10-year periods characterized by low and high EA-WR regimes have been selected. The EA-WR/precipitation correlation patterns have been calculated for each of the periods. Common features that characterize the periods with the two EA-WR regimes are determined. One of the zones with the notable differences between the correlation patterns is found located over the eastern Mediterranean (EM) region. To determine the mechanisms responsible for the differences we analyse the low and high EA-WR low-troposphere circulations characterizing periods with EM precipitation (CEMP). The differences in the correlation patterns are explained by variations in the air mass transport to the EM area during the wet December-February (DJF) months during the two EA-WR regimes. Namely, during the low EA-WR years the CEMP is characterized by mean atmospheric flow transporting the air masses from the Atlantic to the EM. On the contrary, for high EA-WR DJF months the CEMP is typically characterized by advection to the EM of the air masses from central Europe. This finding allows explanation of the observed precipitation decline over the EM during the last several decades of the past century in terms of the positive trend of the EA-WR.