The 3D Structure of Northern Hemisphere Blocking Events: Climatology, Role of Moisture, and Response to Climate Change

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Authors

Ebrahim Nabizadeh , Sandro W Lubis , Pedram Hassanzadeh 

Abstract

We present a comprehensive composite analysis of the 3D structure of blocks and its response to future climate change over North Pacific,
North Atlantic, and Russia in summers and winters. Using reanalysis and two large-ensemble datasets from CESM1 and GFDL-CM3, we investigate the following: The climatology of 3D structure, physical processes governing the temperature anomaly associated with blocks, ability of GCMs to reproduce the 3D structure, and its response to RCP8.5. In reanalysis, over both ocean and land, the anomalous winds are equivalent-barotropic in the troposphere and stratosphere, and temperature anomalies are positive throughout the troposphere
and negative in the lower stratosphere. The main seasonal and regional differences are that blocks are larger/stronger in winters, and over oceans, the temperature anomaly is shifted westward due to latent heating. Analyzing the temperature tendency equation shows that in all three sectors, adiabatic warming due to subsidence is the main driver of the positive temperature anomaly; however, depending on season and region, meridional thermal advection and latent heating might have leading-order contributions too. Both GCMs are found to reproduce the climatological 3D structure remarkably well, but sometimes disagree on future changes. Overall, the future summertime response is
weakening of all fields (except for specific humidity), although the impact on near-surface temperature is not necessarily weakened; e.g., the blocking-driven near-surface warming over Russia intensifies. The wintertime response is strengthening of all fields, except for temperature
in some cases. Responses of geopotential height and temperature are shifted westward in winters, most likely due to latent heating.

DOI

https://doi.org/10.31223/X5H604

Subjects

Atmospheric Sciences, Climate

Keywords

Atmospheric Circulation, Atmospheric blocking events

Dates

Published: 2021-02-16 06:55

Last Updated: 2021-02-16 14:55

License

CC BY Attribution 4.0 International

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