Two types of North American droughts related to different atmospheric circulation patterns
<p>Proxy-based studies suggest that the southwestern USA is affected by two types of summer drought, often termed Dust Bowl-type droughts and 1950s-type droughts. The spatial drought patterns of the two types are distinct. It has been suggested that they are related to different circulation ch...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-12-01
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| Series: | Climate of the Past |
| Online Access: | https://www.clim-past.net/15/2053/2019/cp-15-2053-2019.pdf |
| Summary: | <p>Proxy-based studies suggest that the southwestern USA is affected by two
types of summer drought, often termed Dust Bowl-type droughts and 1950s-type
droughts. The spatial drought patterns of the two types are distinct. It has
been suggested that they are related to different circulation
characteristics, but a lack of observation-based data has precluded further
studies. In this paper, we analyze multi-annual summer droughts in North
America back to 1600 in tree-ring-based drought reconstructions and in a
global, monthly three-dimensional reconstruction of the atmosphere. Using
cluster analysis of drought indices, we confirm the two main drought types
and find a similar catalog of events as previous studies. These two main
types of droughts are then analyzed with respect to 2 m temperatures (T2m),
sea-level pressure (SLP), and 500 hPa geopotential height (GPH) in boreal summer.
1950s-type droughts are related to a stronger wave train over the
Pacific–North American sector than Dust Bowl-type droughts, whereas the
latter show the imprint of a poleward-shifted jet and establishment of a
Great Plains ridge. The 500 hPa GPH patterns of the two types differ
significantly not only over the contiguous United States and Canada but also
over the extratropical North Atlantic and the Pacific. Dust Bowl-type droughts are
associated with positive GPH anomalies, while 1950s-type droughts exhibit
strong negative GPH anomalies. In comparison with 1950s-type droughts, the
Dust Bowl-type droughts are characterized by higher sea-surface temperatures
(SSTs) in the northern North Atlantic. Results suggest that atmospheric circulation
and SST characteristics not only over the Pacific but also over the
extratropical North Atlantic affect the spatial pattern of North American
droughts.</p> |
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| ISSN: | 1814-9324 1814-9332 |