Seasonal variability and synoptic characteristics of dust cases over southwestern Saudi Arabia

Abstract

ABSTRACT:The synoptic characteristics and statistical variability of seasonal dust over southwestern Saudi Arabia are studied for the period from 1979 to 2006 using the aerosol index (AI) from the Total Ozone Mapping Spectrometer (TOMS) satellite, dust observations from surface stations, and meteorological data from the National Center for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis data set.The seasonal AI distribution indicates that approximately 80% of each year was dusty and that most of the dust occurred during hot months. In addition, the surface observations of the dust types show that the stations with the largest number of dust observations throughout the year were close to the desert, except during the summer, when the stations near the Red Sea had the largest number of dust observations.The synoptic forces that influenced the dust cases were the relative positions of high-pressure systems (Azores or Siberian) and low-pressure systems (Sudan or Indian), alongside their interactions. The relative positions of the atmospheric systems are highly pronounced at a pressure level of 850 hPa; at this pressure, the systems are oriented from north (anticyclonic system) to south (cyclonic system), turn anticlockwise to become oriented from west (anticyclonic system) to east (cyclonic system) during the summer, and then turn clockwise during the winter. Moreover, the interaction of the atmospheric systems influences the wind pattern of the seasonal composition over the southern Arabian Peninsula, which produces an anticyclonic wind pattern during winter, a cyclonic wind pattern during spring, a northerly/northwesterly wind pattern during summer and an anticyclonic wind pattern during autumn.The dust sources changed because of the relative positions of these atmospheric systems, in which the 'Toker Gap' Sudan was the summer/autumn dust source, and the 'central and eastern' Arabian Peninsula was the winter/spring dust source.

Monthly and seasonal variability of dust events over northern Saudi Arabia

“…Remote sensing dust data for global absorbing aerosols over land and sea have been retrieved from Total Ozone Mapping Spectrometer (TOMS) instruments (Herman et al, 1997;Torres et al, 1998); these measurements are known as the aerosol index (AI), which represents the difference between the backscattered radiation measurements between 331 and 380 nm (Hsu et al, 1999). Generally, the value of the AI is proportional to the optical depth and dust altitude (Mahowald et al, 2003), but dust near the surface produces a deficiency in the AI values, which can be overcome by using the threshold values (Prospero et al, 2002;Washington et al, 2003;Gao and Washington, 2009;Mashat et al, 2018). The AI data are daily data from the period from November 1978 to 2010, with a data gap from May 1993 to July 1996, and these data have a spatial resolution of 1.25 x 1.0 , where the data from 2007 to 2010 have been interpolated from the original resolution of 1.0 x 1.0 into 1.25 x 1.0 .…”

“…In this study, we used a combination of surface observations, remote sensing, and meteorological data collected over a long period—from 1978 to 2010—to study the variability, temporal and synoptic characteristics of the annual dust over northern Saudi Arabia, rather than that of individual seasons, as was performed in previous studies (e.g., Awad and Mashat, ; Awad et al ., ; Awad and Mashat, ). Another advantage of this study is that the cases for the climate synoptic study were selected from wide surface‐observed dust storms, that is, cases where at least three stations observed the dust storms (not conditional selections from remote sensing data, such as in Mashat et al ., ) and where the composite cases of climatology can be interpreted using remote sensing data. Therefore, this study provides clear examples of the seasonal synoptic features associated with dust storms over a region specified as a dust region climate over the Arabian Peninsula (Middleton, ) that is affected by its own dust (Hamidi et al ., ) and transported dust (Awad and Mashat, ).…”

Spatial and Temporal Variations in the Incidence of Dust Storms in Saudi Arabia Revealed from In Situ Observations

“…Furthermore, climate change might also have an impact on the frequency of dust storms, as drier and hotter conditions may reduce the overall vegetation coverage and, therefore, intensify the desertification process [38,78]. This is particularly important, as recent studies showed that long-term drought conditions linked to synoptic weather conditions (i.e., the configuration of high-pressure and low-pressure systems) control dust storm activities over large areas (e.g., [22,23,79]). This underlines the urgent need for future research investigating the spatio-temporal trends of dust storms across the Arabian Peninsula taking into account large-scale influencing factors such as land-use change and climate change.…”

Climatology of the spring Red Sea Trough

“…Moreover, the Sudan low and the associated RST play an important role in the generation of the synoptic systems of the southern Mediterranean (Almazroui and Awad, ) or affect the daily synoptic systems in the EM region (Alpert et al, ). In addition, the RST influenced the development of the widespread dust over the northern Arabian Peninsula (Mashat and Awad, ) or the southwestern Arabian Peninsula (Mashat et al, ) when a high‐pressure gradient formed over and along the western part of the Arabian Peninsula between the RST and the Arabian Peninsula high pressure (Jish Prakash et al, ). Furthermore, Papadopoulos et al () show that in winter, the joint of Mediterranean low pressure and RST, which was defined in their work as the north extension of the Equatorial African low, induced a positive turbulent flux over the northern Red Sea region, whereas a negative turbulent flux was produced when the RST was located to the south.…”

“…Previous studies demonstrated the importance of the RST extension/shrinking (e.g., Krichak et al, ; Tsvieli and Zangvil, ; de Vri es et a l. ( & ); Papadopoulos et al, ; Haggag and El‐Badry, ) or west–east orientation around the Red Sea (e.g., Tsvieli and Zangvil, , ) on the atmospheric systems and described the effects of weather characteristics of the RST in the Red Sea region. Nevertheless, most RST studies are either case studies (e.g., Haggag and El‐Badry, ; Mashat and Awad, ) or undertaken for short periods of time for specific purposes (e.g., Tsvieli and Zangvil, ; Mashat et al, ) and do not provide deep insights on the synoptic and climate characteristics of the RST and their seasonal variabilities. In addition, those studies do not discuss details or provide specific answers about the synoptic forces that controlled the RST extension–northward/southward shrinking, west–east orientation around the Red Sea and do not quantify the increasing/decreasing RST.…”