Dominant modes and mechanisms of the interannual variability of atmospheric water vapor content during winter over Central Asia

Abstract

Atmospheric water vapor content (WVC)—a key component of the water cycle—plays a crucial role as an indicator of precipitation changes and directly influences precipitation in the arid areas of Central Asia. These areas are extremely sensitive to global climate change because of their dry climates and fragile water resource systems, especially during winter. This study analyzes the main interannual variation patterns of the atmospheric WVC during winter over Central Asia and reveals the possible physical mechanism behind the changes in the dominant modes (EOF1 and EOF2) of water vapor. The results show that EOF1 (49.4%)—responsible for the interannual variation of the winter atmospheric WVC in Central Asia—has a uniform monopole mode, while EOF2 (23.7%) shows a reverse north–south dipole distribution (with the boundary being at approximately 44° N). The negative geopotential height anomaly over the high latitudes of Europe and the positive geopotential height anomaly over Central Asia are the major impact factors of EOF1, whereas Central Asia has a prevalence of westerly airflow during winter. By influencing the geopotential height anomaly in Central Asia, the winter Niño 3.4 index intensifies the convergence of Atlantic Ocean moisture with tropical Indian Ocean moisture and their eastward transport. In contrast, EOF2 is mainly affected by the positive geopotential height anomaly over the high latitudes of Europe and the negative geopotential height anomaly over the middle latitudes of this region. In particular, the negative anomaly center of the geopotential height on the eastern side of Central Asia extends westward into Central Asia, resulting in reverse moisture transport by westerly and easterly airflows in the southern and northern parts of Central Asia, respectively. This anomaly is correlated with the formation of anomalous cyclonic circulation over North Africa and Europe because of the negative phase of the Arctic Oscillation, leading to prevailing southerly winds in the south of Central Asia, which correspond to abnormal vertical upward movement; however, the situation in the northern part of Central Asia is the opposite. Therefore, the distribution of winter precipitation in Central Asia shows the following pattern: more in the south and less in the north. This study provides scientific and technological support for the formation of research mechanisms and the prediction of winter precipitation in Central Asia.