Iranian Journal of Geophysics

Iranian Journal of Geophysics

Climatological study of the ITCZ location in the Indian ocean region for the period 1983-2023

Document Type : Research Article

Authors
Abbas Entezari 1
Farhang Ahmadi-Givi 2
Mohammad Mirzaei 3
1 M.Sc., Institute of geophysics, University of Tehran, Tehran, Iran
2 Professor, Institute of geophysics, University of Tehran, Tehran, Iran
3 Associate Professor, Institute of geophysics, University of Tehran, Tehran, Iran
10.30499/ijg.2026.561749.1739
Abstract
The Intertropical Convergence Zone (ITCZ), the ascending branch of the Hadley meridional circulation, plays a crucial role in the tropical and extratropical climate through the transfer of energy, momentum, and mass. The key factors contributing to the formation of the ITCZ include the convergence of trade winds, high sea surface temperatures (SSTs), and sufficient surface moisture. Although extensively studied, the ITCZ over the Indian Ocean has received comparatively less attention than extreme monsoonal rainfall events. Shifts in the location or intensity of the ITCZ can modulate the descending branch of the Hadley cell, driving meridional displacements of subtropical high-pressure systems. Accordingly, examining spatial fluctuations of the ITCZ and their impacts on the climate of countries bordering the Indian Ocean, Southwest Asia, and the southern Iranian Plateau is of considerable importance. This study employs the ERA5 reanalysis data at 0.25° spatial resolution in both latitude and longitude for the period 1983–2023. Analyses are conducted for two extreme months—February and July—as well as the seasons of summer (December, January, February) and winter (June, July, August) in the Southern Hemisphere. Meteorological parameters used in this study include convective precipitation, SST, horizontal wind vectors, temperature, dew point temperature, potential temperature, equivalent potential temperature, saturated equivalent potential temperature, and vertical velocity at different pressure levels. Using these variables, the position of the ITCZ in the Indian Ocean region was identified, then thermodynamic factors in the boundary layer and free atmosphere contributing to its formation were analyzed. Additionally, based on convective precipitation data, the latitudinal position of ITCZ occurrences was calculated, and its spatial distribution across the extreme months and seasons was determined.
Results indicate that the highest probability of ITCZ occurrence—in terms of both intensity and spatial extent—is seen between 10°S and 12°S during the austral summer. Factors such as elevated moist static energy (equivalent potential temperature), the development of warm air masses accompanied by SSTs around 300 Kelvin or higher, and strong SST gradients—acting as enhancers of horizontal wind vectors—play significant roles in initiating deep convective processes. Moreover, the intensification of vertical velocity resulting from the convergence of horizontal wind vectors can act as a forcing mechanism on moist air parcels with sufficient moist static energy, leading to the formation of the ITCZ over the Indian Ocean. In addition to identifying ITCZ during the austral summer in the southern Indian Ocean, the study also highlights the occurrence of a double ITCZ during the austral autumn and winter, attributed to the symmetrical meridional distribution of convective precipitation in the western Indian Ocean region. Another notable finding is the formation of a stable cold oceanic tongue south of the convergence zone, characterized by an SST difference of about 1 Kelvin. Vertical profiling of variables such as equivalent potential temperature, saturated equivalent potential temperature, relative humidity, and vertical velocity clearly illustrates the contrast between the area influenced by the cold oceanic tongue and the surface convergence zone in terms of static stability.
Keywords
Indian ocean
intertropical convergence zone
cold oceanic tongue
sea surface temperature
convective precipitation
Subjects
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Iranian Journal of Geophysics
Volume 20, Issue 4
September and October 2026
Pages 77-94

  • Receive Date 23 November 2025
  • Revise Date 03 June 2026
  • Accept Date 06 June 2026
  • First Publish Date 06 June 2026
  • Publish Date 23 July 2026