Climate Monitoring of Wind in the Free Atmosphere of the Northern Hemisphere: Long-Term Characteristics and Variability Trends

Abstract

Wind in the free atmosphere is one of the processes recommended by the World Meteorological Organization for climate monitoring. An analysis of the wind regime on large spatial scales presents specific difficulties, since both the vertical and horizontal distributions of wind speed are highly variable. In order to have an idea about the general characteristics of the wind regime in the main atmospheric layers, the Russian Institute of Hydrometeorological Information, World Data Center (RIHMI-WDC), developed a method for monitoring the wind regime of the free atmosphere over the territory of the Russian Federation. The goal of this article is to further develop these works both in relation to the region and in terms of research fields. The article presents the results of monitoring the wind speed in the free atmosphere not only over the territory of Russia, but also over the entire Northern Hemisphere, compares the results of radio sounding data and the ERA5 fifth-generation reanalysis data, and it also considers trends in variability of the wind regime over the period 1985–2018. An analysis of wind characteristics in the troposphere and lower stratosphere of the Northern Hemisphere has been carried out in accordance with the technique developed earlier for monitoring the wind regime of wind speed in the free atmosphere. The analysis was extended to the entire Northern Hemisphere using two data sources: an array of long-term radiosonde measurements performed at Russian Institute of Hydrometeorological Information, World Data Center (RIHMI-WDC) and fifth-generation ERA5 reanalysis. The monitoring results based on the two data sources are qualitatively and quantitatively consistent with each other in the areas covered by the network of aerological stations, except for individual high-mountain regions. The distribution of long-term averages in general terms coincides with the distribution of wind speed based on earlier studies. At the same time, each year is distinguished by its own characteristics, displacements of zones of weak and strong winds, and their intensity. Variability trends over the period 1985–2018 in different regions of the Northern Hemisphere were oppositely directed. The strongest negative wind speed trends reaching –1.5 m s^–1 over 10 years occurred in the lower stratosphere north of 55°–60° N. This may indicate a weakening of the winter west–east transport in this region. In the latitudinal belt 30°–45° N over the Eurasian region, on the contrary, positive trends reaching 1.1 m s^–1 over 10 years have been observed.