Abstract
Abstract. Atmospheric blocking represents a weather pattern where a stationary high-pressure system weakens or reverses the climatological westerly flow at mid-latitudes for up to several weeks. It is closely connected to strong anomalies in key atmospheric variables such as geopotential height, temperature, and humidity. Here we provide, for the first time, a comprehensive, global perspective on atmospheric blocking and related impacts by using an observation-based data set from Global Positioning System (GPS) radio occultation (RO) from 2006 to 2016. The main blocking regions in both hemispheres and seasonal variations are found to be represented well in RO data. The effect of blocking on vertically resolved temperature and humidity anomalies in the troposphere and lower stratosphere is investigated for blocking regions in the Northern and Southern hemispheres, respectively. We find a statistically significant correlation of blocking with positive temperature anomalies, exceeding 3 K in the troposphere, and a reversal above the tropopause with negative temperature anomalies below −3 K in the lower stratosphere. Specific humidity is positively correlated with temperature throughout the troposphere with larger anomalies revealed in the Southern Hemisphere. At the eastern and equatorward side of the investigated blocking regions, a band of tropospheric cold anomalies reveals advection of cold air by anticyclonic motion around blocking highs, which is less distinct in the Southern Hemisphere due to stronger zonal flow. We find GPS RO to be a promising new data set for blocking research that gives insight into the vertical atmospheric structure, especially in light of the expected increase in data coverage that future missions will provide.
Highlights
Global weather and climate are determined by different processes such as the jet stream, the storm tracks, and blocking
In this study we provide, for the first time, a global perspective on atmospheric blocking based on the radio occultation (RO) record from September 2006 to August 2016 exploiting its good vertical resolution for investigating the atmospheric vertical structure in temperature and humidity during blocking events
All four data sets agree on the two main blocking regions in the Northern Hemisphere (NH) (Fig. 1a)
Summary
Global weather and climate are determined by different processes such as the jet stream, the storm tracks, and blocking. Lejenäs, 1984; de Adana and Colucci, 2005) Due to this imbalance comparably few studies investigate blocking in the SH, mostly focusing on impacts in Australia and New Zealand (Australian–New Zealand blocking region) and in South America (south-eastern Pacific blocking region) Reanalyses combine an atmospheric model with a range of observations from different measurement systems to approximate the atmospheric state as accurately as possible Due to this data assimilation the accuracy of reanalyses is less well understood compared to observations (Parker, 2016). GPS RO provides highly accurate measurements of atmospheric variables and has the potential to complement models and reanalyses as data set for blocking research.
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