J. Barkan

Chapter 2 Relations between climate variability in the Mediterranean region and the tropics: ENSO, South Asian and African monsoons, hurricanes and Saharan dust

Publisher Summary The Mediterranean climate is affected by several tropical and subtropical systems as illustrated by some evidence presented in this chapter. These factors range from the El Nino Southern Oscillation (ENSO) and tropical hurricanes to the South Asian Monsoon and Saharan dust. This leads to complex features in the Mediterranean climate variability. It reviews some tropical and subtropical teleconnections to the Mediterranean climate. It discusses the South Asian Monsoon (SAM), which is a key factor influencing the climate of the eastern and central Mediterranean. It causes high variability in sea level pressure (SLP) over Arabia and the Middle East with high pressures in winter and low pressures in summer. The adjustment to the SAM couples the falling pressure and land temperature over the Indian subcontinent/Asia Minor with rising pressure and temperature over the Persian Gulf and Iraq. Red Sea Trough intrusions into the Eastern Mediterranean and the Saharan dust are also discussed in the chapter.

Atmospheric response to Saharan dust deduced from ECMWF reanalysis (ERA) temperature increments

This study focuses on the atmospheric temperature response to dust deduced from a new source of data—the European Reanalysis (ERA) increments. These increments are the systematic errors of global climate models, generated in the reanalysis procedure. The model errors result not only from the lack of desert dust but also from a complex combination of many kinds of model errors. Over the Sahara desert the lack of dust radiative effect is believed to be a predominant model defect which should significantly affect the increments. This dust effect was examined by considering correlation between the increments and remotely sensed dust. Comparisons were made between April temporal variations of the ERA analysis increments and the variations of the Total Ozone Mapping Spectrometer aerosol index (AI) between 1979 and 1993. The distinctive structure was identified in the distribution of correlation composed of three nested areas with high positive correlation (>0.5), low correlation and high negative correlation (< −0.5). The innermost positive correlation area (PCA) is a large area near the center of the Sahara desert. For some local maxima inside this area the correlation even exceeds 0.8. The outermost negative correlation area (NCA) is not uniform. It consists of some areas over the eastern and western parts of North Africa with a relatively small amount of dust. Inside those areas both positive and negative high correlations exist at pressure levels ranging from 850 to 700 hPa, with the peak values near 775 hPa. Dust-forced heating (cooling) inside the PCA (NCA) is accompanied by changes in the static instability of the atmosphere above the dust layer. The reanalysis data of the European Center for Medium Range Weather Forecast (ECMWF) suggest that the PCA (NCA) corresponds mainly to anticyclonic (cyclonic) flow, negative (positive) vorticity and downward (upward) airflow. These findings are associated with the interaction between dust-forced heating/cooling and atmospheric circulation. This paper contributes to a better understanding of dust radiative processes missed in the model.

Synoptics of dust intrusion days from the African continent into the Atlantic Ocean

well as the difference between them (intrusion minus no intrusion), in the area (60� W– 25� E, 0� –60� N), were analyzed. For both intrusion and no-intrusion days a closed high pressure, centered at approximately (45� W, 32� N), was found, with a ridge northeastward. EastoftheridgewasatroughlocatedtothewestoftheEuropeanandthenorthAfricancoast. Further east was a closed high in the western Sahara with a ridge northeastward. Each of the maps presenting the difference between the two aforementioned variables shows two highs: one over western Europe and the other, quite strong, west of the African coast on the 24� N–25� N latitudes. Between them, centered about (15� W, 37� N), there is a low-pressure area. As a result of the higher pressure at the African anticyclone in the intrusion cases, an easterly-northeasterly flow dominates at the latitudes 18� N–22� N, which presumably causes the dust intrusion from the continent into the Atlantic. Correlation between the Total Ozone Mapping Spectrometer aerosol index on the one hand and the wind magnitude and theuandvcomponentsontheotherhandwasalsoanalyzedfortheentiredataset.Correlation coefficients of r = 0.52, r = � 0.46, and r = � 0.27 were found. Analysis of two extreme intrusion and no-intrusion cases inJuly 1983 demonstrates the synoptic situation that allows the Saharan dust to reach England and NW Europe. INDEX TERMS: 0305 Atmospheric CompositionandStructure:Aerosolsandparticles(0345,4801);3309MeteorologyandAtmosphericDynamics: Climatology (1620); 3364 Meteorology and Atmospheric Dynamics: Synoptic-scale meteorology; KEYWORDS: Sahara, dust transport, dust intrusion

Dust as a Potential Tracer for the Flow over Different Topographical Shapes Employing MODIS-Terra Observations

The hypothesis, that the magnitude of the Froude number can represent the flow type around an obstacle was examined at several different topographical shapes in dust-laden environments. It was found that in most cases this hypothesis was true. Average of 16 May months AOT data extracted from the MODIS Terra satellite has shown that in case of Froude number less than one, the AOT isolines tend to follow the topographical contours of the mountain peak (the obstacle) along with a minimum AOT near the peak.