Climatology of the heat low and the intertropical discontinuity in the Arabian Peninsula

Abstract

In this article, the climatological state and the seasonal variability of the Arabian heat low (AHL) and the intertropical discontinuity (ITD) are investigated over the Arabian Peninsula using the 1979-2019 ERA-5 reanalysis data.The AHL is a summertime feature, mostly at 15 -35 N and 40 -60 E, exhibiting a clear strengthening over the last four decades in line with the observed increase in surface temperature. However, no clear shift in its position is detected. The AHL, driven by both thermodynamic and dynamic forcing, is broader and stronger during daytime and exhibits considerable variability on day-to-day timescales, likely due to the convection associated with the Asian summer monsoon. The ITD is the boundary between the hot and dry desert air and the cooler and more moist air from the Arabian Sea. It lies along the Arabian Peninsula's southern coastline in the cold season but reaches up to 28 N between 50 and 60 E in the summer months. While in the former it has a rather small diurnal variability; in the latter it shows daily fluctuations of up to 10 in latitude. The presence of the Sarawat Mountains over southwestern Saudi Arabia precludes a northward migration of the ITD in this area. The ITD exhibited a weak northward migration in the 41-year period, likely due to the increased sea surface temperatures in the Arabian Sea. On inter-annual timescales, the El Niño-Southern Oscillation, the Indian Ocean Dipole, and solar-geomagnetic effects play an important role in the AHL's and ITD's variability.

Convection-Aerosol Interactions in the United Arab Emirates: A Sensitivity Study

“…Despite the small decrease in the the downward shortwave radiation flux, however, WRF continues to largely overestimate the observed values, which can be attributed to a lack of clouds in the model, a bias that has been noted by several authors (e.g. Wehbe et al, 2019;Fonseca et al, 2020;. Given the lack of clouds, the ARI effects will prevail over the ACI effects, and hence the model predictions for simulations WRF-1 to WRF-4 will be comparable, as seen in Fig.…”

“…The meager and irregular amounts of precipitation, which range from less than 40 mm in the southern desert to over 120 mm over the mountains, mostly fall in the cold season from November to March, in association with mid-latitude weather systems (Niranjan Kumar and Ouarda, 2014;Wehbe et al 2017Wehbe et al , 2018. However, summertime convective events are present as well, and can lead to rainfall accumulations of more than 100 mm and flash floods at isolated sites (Steinhoff et al, 2018;Wehbe et al, 2020;Francis et al, 2021).…”

“…Convection in the warm season in the UAE tends to take place on the eastern half of the country, around the Al Hajar mountains. As discussed in Schwitalla et al (2020) and , it is normally triggered by the convergence of the low-level circulation associated with the Arabian Heat Low (AHL; Fonseca et al, 2021), the sea-breeze circulation from the Arabian Gulf and Sea of Oman, and the upslope flows on the mountains. The presence of a mid-to upper-level trough, originating from the mid-latitudes, and associated unstable stratification also promotes the development of convective clouds (Francis et al, 2021).…”

“…Ocean (Yu et al, 2015) and in the equatorial Pacific (Fonseca et al, 2021). A stronger AHL, typically seen during periods of enhanced convective activity over the Arabian Sea, as the increased descent and subsidence over the Arabian Peninsula helps to intensity the heat low, modulates the inland penetration of the marine boundary layer.…”

“…Francis et al, 2020) storms, is labelled as the Intertropical Discontinuity (ITD). Its position is therefore linked to the strength and spatial extent of the AHL, as explained in Fonseca et al (2021).…”