Climatology and Interannual Movements of Upper-Level Frontal Zones in the Middle Troposphere of the Northern Hemisphere

Abstract

Based on the use of an objective methodology that takes into account the local values of the geopotential gradients, the long-term average position of the upper-level frontal zones (UFZs) in the middle troposphere for the Northern Hemisphere over the period of 1948–2014 is calculated for the first time. The procedure for determining UFZs has consisted in estimation of the monthly-average fields of the module of a horizontal geopotential gradient by the approximation of derivatives using the central difference method. Based on the obtained fields of geopotential gradients, the local highs were identified and the positions of the upper-level frontal zones in different seasons were found. The updated climatology of UFZs significantly refines the earlier information, specifying the position of UFZs and identifying, e.g., UFZs that exist only in particular seasons. The estimates of the interannual movements of HAVZs are also obtained for the first time, which makes it possible to analyze the mechanisms of the observed climate variability in different regions of the Earth.