A Statistical Investigation of the Impact of the Indian Monsoon on the Eastern Mediterranean Circulation

Abstract

The Indian summer monsoon (ISM) is a prominent feature of the summer circulation in the Northern Hemisphere (NH) and has been found to modulate the weather and climate conditions in many remote regions. This study investigates the most recurrent patterns of summertime midlatitude circulation, over the eastern Mediterranean (EM) and also globally, that are most associated with the ISM. Monthly data of 44 summers from the ERA40 dataset are used and two multidimensional statistical methods, the Principal Component Analysis (PCA) and Canonical Correlation Analysis (CCA), are implemented. The ISM is found to be related to subsidence anomalies in the middle and more extendedly in the upper troposphere over the central and eastern Mediterranean and with an Etesian-like pattern regarding the field of the lower troposphere winds. An equatorial Rossby wave pattern, extending westward from an ISM heat source up to EM and N. Africa, was identified to be associated with the variability of ISM. The observed relationship between the ISM and the EM circulation features can be attributed to this equatorial Rossby wave response to the monsoon forcing. CCA implementation revealed the interconnection of the aforementioned PCA results with an ISM action center over the northern Arabian Sea and the monsoon trough region.

Etesians and the summer circulation over East Mediterranean in Coupled Model Intercomparison Project Phase 5 simulations: Connections to the Indian summer monsoon

“…Figure presents the seasonal variability of the mean monthly Ω500 for the areas of EMED, BoB and wISM. The subsidence over EMED and the northerly flow over the Aegean is synchronous with the convection of monsoon in northern India and the BoB as reported by earlier studies (Tyrlis et al ., ; Rizou et al ., ; Rizou et al ., ) and shown here in Figure . The descent circulation over EMED and the intensity of Etesians provide an evidence of their common dynamical cause (Tyrlis et al ., ).…”

“…As an expansion of monsoon activity (from the west of ISM to south EMED), the Persian Low (Persian Trough) contributes to the establishment of pressure gradient over EMED. As a result, the Etesian flow over the Aegean Sea is the dominant wind pattern for the EMED (Tyrlis and Lelieveld, ; Rizou et al ., ).…”

“…Finally, as shown here, ESMs can reliably capture the association between the monsoon circulation over the areas of wISM/BoB and the circulation over EMED. Our work supports the role of the Indian monsoon (as suggested by Tyrlis et al ., ; Rizou et al ., ) in the modulation of Etesian winds, the circulation over eastern Mediterranean and the links between the two regions during summer.…”

“…Past studies have analysed the Etesians and the linkage between EMED and ISM region (shown in Figure ) during the extended summer based on observations and reanalysis data (Ziv et al ., ; Tyrlis et al ., ; Rizou et al ., ; Dafka et al ., ; Rizou et al ., ). However, there is no previous study investigating the long‐term variability of Etesians and the linkage of atmospheric circulation between EMED and Bay of Bengal (ΒoΒ)/west Indian summer monsoon (wISM) using ESMs simulations participating to Coupled Model Intercomparison Project Phase 5 (CMIP5).…”

“…Etesians are the result of large‐scale synoptic circulation in the area of the Balkan and East Mediterranean (17°–31°E and 30°–41°N; hereafter EMED) (Hoskins and Rodwell, ; Kallos et al ., ; Anagnostopoulou et al ., ; Rizou et al ., ) when the combination of low‐pressure centre over south EMED and a high‐pressure system over central Europe/North Balkans leads to cold air transfer from Russia and the Caspian Sea. The topography of the region with the mountains in continental Greece and Turkey, Bosporus and the Dardanelles straights canalize the winds and act as a ventilating system for the south EMED (Jimenez et al ., ; Poupkou et al ., ; Tyrlis et al ., ).…”