Detection of upwelling events in the Caspian Sea using thermal satellite image processing

Abstract

In this article, we studied the upwelling phenomena observed in the surface waters of the Caspian Sea. Studying upwelling is crucial for understanding and managing the complex interactions between the ocean, climate, and marine life, with implications for both environmental conservation and human well-being. To accomplish this, we utilized data from MODIS-Aqua satellite observations in the infrared range of 11 microns. These observations had a spatial resolution of 4 km and covered the period from 2003 to 2021. The data was accessed through the NASA Giovanni online data system databases. Our findings indicate that upwelling phenomena are primarily observed in the eastern part of the Middle and South Caspian from May to September. The most intense upwelling occurs along the eastern coast of the Middle Caspian in July and August. Based on long-term averaged data, the upwelling phenomenon is typically observed between 40-44º latitude during this period. The width of the upwelling zone increases gradually from north to south, extending approximately 60-70 km towards the Kazakh Gulf before decreasing towards the south. In the upwelling zone, the temperature gradient can at times reach 4.0ºC per 100 km. In certain years, the upwelling zone that initially forms along the eastern coasts can extend over long distances and even reach the western coasts. Generally, the upwelling phenomenon occurs alongside the advection of warm waters from the South Caspian towards the Middle Caspian.