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of the 2008 drought were carried out with the Advanced Research WRF (ARW), version 3.2, released on 2 April 2010. A full technical description of the system is given in Skamarock et al. (2008) . WRF solves the fully compressible nonhydrostatic Eulerian equations in flux form, using a terrain-following hydrostatic pressure vertical coordinate. It is coupled with the Noah LSM version 3.2 that solves the surface energy and water balances to provide sensible and latent heat fluxes to the boundary
of the 2008 drought were carried out with the Advanced Research WRF (ARW), version 3.2, released on 2 April 2010. A full technical description of the system is given in Skamarock et al. (2008) . WRF solves the fully compressible nonhydrostatic Eulerian equations in flux form, using a terrain-following hydrostatic pressure vertical coordinate. It is coupled with the Noah LSM version 3.2 that solves the surface energy and water balances to provide sensible and latent heat fluxes to the boundary
for (b) MAM, (c) JJA, and (c) OND. Data are from GPCC. Monthly averaged values of various atmospheric variables contained in the National Centers for Environmental Prediction (NCEP) Reanalysis 1 product (R1; Kalnay et al. 1996 ) were employed. The gridded R1 data cover the period 1948–2013 and are at 2.5° latitude–longitude resolution. Vertically integrated (850–500 hPa) moisture flux anomalies were computed using R1, the anomalous flux being separated into three terms: where the subscripts m
for (b) MAM, (c) JJA, and (c) OND. Data are from GPCC. Monthly averaged values of various atmospheric variables contained in the National Centers for Environmental Prediction (NCEP) Reanalysis 1 product (R1; Kalnay et al. 1996 ) were employed. The gridded R1 data cover the period 1948–2013 and are at 2.5° latitude–longitude resolution. Vertically integrated (850–500 hPa) moisture flux anomalies were computed using R1, the anomalous flux being separated into three terms: where the subscripts m
principal component (PC1) are shown in Figs. 6a,b . The fractional variance explained by the EOF1 is 39.8% and can well separate from other modes based on the north’s criteria ( North et al. 1982 ). The Silk Road pattern features a wave train structure along the Asian jet ( Fig. 6a ), with four centers located near 40°, 65°, 95°, and 130°E. The center near 130°E in EOF1 was associated with the Bonin high, as discussed by Enomoto et al. (2003) . The wave activity flux propagated eastward along the
principal component (PC1) are shown in Figs. 6a,b . The fractional variance explained by the EOF1 is 39.8% and can well separate from other modes based on the north’s criteria ( North et al. 1982 ). The Silk Road pattern features a wave train structure along the Asian jet ( Fig. 6a ), with four centers located near 40°, 65°, 95°, and 130°E. The center near 130°E in EOF1 was associated with the Bonin high, as discussed by Enomoto et al. (2003) . The wave activity flux propagated eastward along the
are probably unable to produce an important class of precipitation event for the Fertile Crescent. Given the extreme terrain throughout most of the region and the scarcity of observations, it is not clear that current gridded global analyses adequately represent regional moisture fluxes. The seasons in the Persian Gulf area of the region are sometimes divided into the northeast monsoon (December–March), the spring transition (April–May), the southwest monsoon (June–September), and the fall
are probably unable to produce an important class of precipitation event for the Fertile Crescent. Given the extreme terrain throughout most of the region and the scarcity of observations, it is not clear that current gridded global analyses adequately represent regional moisture fluxes. The seasons in the Persian Gulf area of the region are sometimes divided into the northeast monsoon (December–March), the spring transition (April–May), the southwest monsoon (June–September), and the fall
in the troposphere, in association with a relative subsidence, which in turn weakens the monsoon flow and reduces moisture flux convergence and lowers rainfall. It has also been found that the Sahel, along with a few other regions that are mostly semiarid, has the largest soil moisture/climate coupling strength in the world. This result was obtained in the Global Land–Atmosphere Coupling Experiment (GLACE; Koster et al. 2006 ). Two sets of boreal summer (June–August) simulations were performed
in the troposphere, in association with a relative subsidence, which in turn weakens the monsoon flow and reduces moisture flux convergence and lowers rainfall. It has also been found that the Sahel, along with a few other regions that are mostly semiarid, has the largest soil moisture/climate coupling strength in the world. This result was obtained in the Global Land–Atmosphere Coupling Experiment (GLACE; Koster et al. 2006 ). Two sets of boreal summer (June–August) simulations were performed
. Anomalous warming of the southern tropical Atlantic enhances ascent over the Gulf of Guinea and descent over the Sahel. A warming in the Pacific and Indian Oceans generates equatorial Rossby waves that contribute to subsidence over the Sahel and thus to reduce regional precipitation. In addition, Mediterranean warm events are linked to increased moisture flux convergence over the Sahel. Decadal SST variability and global warming are also relevant to Sahelian drought. In recent decades the Sahel has been
. Anomalous warming of the southern tropical Atlantic enhances ascent over the Gulf of Guinea and descent over the Sahel. A warming in the Pacific and Indian Oceans generates equatorial Rossby waves that contribute to subsidence over the Sahel and thus to reduce regional precipitation. In addition, Mediterranean warm events are linked to increased moisture flux convergence over the Sahel. Decadal SST variability and global warming are also relevant to Sahelian drought. In recent decades the Sahel has been
tendency toward wetter conditions throughout the twentieth century. Frey and Smith (2003) examined precipitation and temperature trends in station observations from western Siberia, a region with a large percentage of the world’s peatlands, and one that contributes substantially to the terrestrial freshwater flux into the Arctic Sea. They found robust patterns of springtime warming and wintertime precipitation increases, with the Arctic Oscillation (AO) playing an important role in nonsummer warming
tendency toward wetter conditions throughout the twentieth century. Frey and Smith (2003) examined precipitation and temperature trends in station observations from western Siberia, a region with a large percentage of the world’s peatlands, and one that contributes substantially to the terrestrial freshwater flux into the Arctic Sea. They found robust patterns of springtime warming and wintertime precipitation increases, with the Arctic Oscillation (AO) playing an important role in nonsummer warming
