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

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.