Abstract
A meridional Northern Hemisphere (NH) circulation epoch, which began in 1957, is marked by changes in the temperature and precipitation regimes over southwest Russia and central USA depending on the occurrence of NH atmospheric circulation regimes. A classification scheme proposed in 1968, and studied later put forth 13 NH circulation types, fitting more broadly into four groups, two of which are more zonal type flows and two of which are more meridional flows. Using the results of a previous study that showed four distinct sub-periods during the 1957–2017 epoch, the temperature and precipitation regimes of both regions were studied across all seasons in order to characterize modern day climate variability and their suitability for vegetation growth. Then the Hydrologic Coefficient, which combined the temperature and precipitation variables, was briefly studied. The most optimal conditions for vegetation growth, positive temperature and precipitation anomalies, were noted during the period 1970–1980 for southwest Russia, which was dominated by an increasingly more zonal flow regime in the Belgorod region and NH in general. For the central USA, the HTC showed more ideal conditions for agriculture in recent years due to favorable precipitation occurrence. In southwest Russia, variable precipitation regimes were noted during the meridional flow periods, and with the increase in temperature (since 1998), these can adversely affect the hydrothermal characteristics of the growing season. Finally, a comparison of the 13 NH circulation types with several teleconnection indexes demonstrated the robustness of the NH flow regime classification scheme used here.
Highlights
Since the end of the 20th century, climate change has been associated with increases in observed temperatures globally [1]
The early work of references [52,53,54] suggested the Northern Hemisphere (NH) flow vacillated between two quasi-stable states, but later work suggested that the NH flow possesses multiple stable states, including those that represent blocking
As explained in reference [7], many of the sub-types are characterized locally by a trough or ridge, for example, two quasi-stable states, but later work suggested that the NH flow within a particular region. stable states, possesses multiple
Summary
Since the end of the 20th century, climate change has been associated with increases in observed temperatures globally [1] These increases have not been uniform on regional spatial scales (e.g., reference [1]). Reference [4] used global temperature data provided by the University of East Anglia [5] for the period 1850–2009 and noted the cyclical nature of changes in annual average NH temperature. These cyclical changes have been imprinted on an overall increase in NH or global temperature since. In examining the Northern Hemisphere (NH) temperature record since 1950 (e.g., reference [1]), many researchers have noted periods of warming and cooling (e.g., references [2,3]).
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