Early Spring in Europe: A Result of More Dominant North-Atlantic Southwesterlies?
Abstract A 1999 study reports an advancement of spring in Europe by 0.2 days per year in the 30 years since 1960. Our analysis indicates that this trend results directly from a change in the late-winter surface winds over the eastern North Atlantic: the southwesterly direction became more dominant,...
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ftnasantrs:oai:casi.ntrs.nasa.gov:20000097046 2023-05-15T17:30:12+02:00 Early Spring in Europe: A Result of More Dominant North-Atlantic Southwesterlies? Atlas, R. Otterman, J. Einaudi, Franco Sud, Y. C. Rogers, J. Russell, G. L. Schubert, S. D. Pielke, R. A., Sr. Chou, S.-H. Chase, T. N. Jusem, J. C. Unclassified, Unlimited, Publicly available [2000] application/pdf http://hdl.handle.net/2060/20000097046 unknown Document ID: 20000097046 http://hdl.handle.net/2060/20000097046 No Copyright CASI Meteorology and Climatology 2000 ftnasantrs 2015-03-15T02:39:26Z Abstract A 1999 study reports an advancement of spring in Europe by 0.2 days per year in the 30 years since 1960. Our analysis indicates that this trend results directly from a change in the late-winter surface winds over the eastern North Atlantic: the southwesterly direction became more dominant, and the speed of these southwesterlies increased slightly. Splitting the 52-year NCEP reanalysis dataset into the First Half, FH (1948-1973)), and the Second Half, SH (1974-1999), we analyze the wind direction for the February mean at three sites at 45N: site A at 30W, site B at 20W, and site C at 10W. The incidence (number of years) of the southwesterlies in SH Vs. (FH) at these sites respectively increased in SH as follows: 24(18), 19(12), 14(l 1); whereas the incidence of northeasterlies decreased: 0(2), 1(2), and 1(6). When the February mean wind is southwesterly, the monthly mean sensible heat flux from the ocean at these sites takes zero or slightly negative values, that is, the surface air is warmer than the ocean. Analyzing the scenario in the warm late winter 1990, we observe that the sensible heat flux from the ocean surface in February 1990 shows a "tongue" of negative values extending southwest from southern England to 7N. This indicates that the source of the maritime air advected into Europe lies to the south of the "tongue." Streamline analysis suggests that the Southwestern or southcentral North Atlantic is the source. For February 1990, we find strong, ascending motions over Europe at 700 mb, up to -0.4 Pa/s as monthly averages. Associated with the unstable low-levels of the troposphere are positive rain and cloud anomalies. Thus, positive in situ feedback over land in late winter (when shortwave absorption is not significant) apparently further enhances the surface temperature through an increase in the greenhouse effect due to increased water vapor and cloudiness. Other/Unknown Material North Atlantic NASA Technical Reports Server (NTRS) |
institution |
Open Polar |
collection |
NASA Technical Reports Server (NTRS) |
op_collection_id |
ftnasantrs |
language |
unknown |
topic |
Meteorology and Climatology |
spellingShingle |
Meteorology and Climatology Atlas, R. Otterman, J. Einaudi, Franco Sud, Y. C. Rogers, J. Russell, G. L. Schubert, S. D. Pielke, R. A., Sr. Chou, S.-H. Chase, T. N. Jusem, J. C. Early Spring in Europe: A Result of More Dominant North-Atlantic Southwesterlies? |
topic_facet |
Meteorology and Climatology |
description |
Abstract A 1999 study reports an advancement of spring in Europe by 0.2 days per year in the 30 years since 1960. Our analysis indicates that this trend results directly from a change in the late-winter surface winds over the eastern North Atlantic: the southwesterly direction became more dominant, and the speed of these southwesterlies increased slightly. Splitting the 52-year NCEP reanalysis dataset into the First Half, FH (1948-1973)), and the Second Half, SH (1974-1999), we analyze the wind direction for the February mean at three sites at 45N: site A at 30W, site B at 20W, and site C at 10W. The incidence (number of years) of the southwesterlies in SH Vs. (FH) at these sites respectively increased in SH as follows: 24(18), 19(12), 14(l 1); whereas the incidence of northeasterlies decreased: 0(2), 1(2), and 1(6). When the February mean wind is southwesterly, the monthly mean sensible heat flux from the ocean at these sites takes zero or slightly negative values, that is, the surface air is warmer than the ocean. Analyzing the scenario in the warm late winter 1990, we observe that the sensible heat flux from the ocean surface in February 1990 shows a "tongue" of negative values extending southwest from southern England to 7N. This indicates that the source of the maritime air advected into Europe lies to the south of the "tongue." Streamline analysis suggests that the Southwestern or southcentral North Atlantic is the source. For February 1990, we find strong, ascending motions over Europe at 700 mb, up to -0.4 Pa/s as monthly averages. Associated with the unstable low-levels of the troposphere are positive rain and cloud anomalies. Thus, positive in situ feedback over land in late winter (when shortwave absorption is not significant) apparently further enhances the surface temperature through an increase in the greenhouse effect due to increased water vapor and cloudiness. |
author |
Atlas, R. Otterman, J. Einaudi, Franco Sud, Y. C. Rogers, J. Russell, G. L. Schubert, S. D. Pielke, R. A., Sr. Chou, S.-H. Chase, T. N. Jusem, J. C. |
author_facet |
Atlas, R. Otterman, J. Einaudi, Franco Sud, Y. C. Rogers, J. Russell, G. L. Schubert, S. D. Pielke, R. A., Sr. Chou, S.-H. Chase, T. N. Jusem, J. C. |
author_sort |
Atlas, R. |
title |
Early Spring in Europe: A Result of More Dominant North-Atlantic Southwesterlies? |
title_short |
Early Spring in Europe: A Result of More Dominant North-Atlantic Southwesterlies? |
title_full |
Early Spring in Europe: A Result of More Dominant North-Atlantic Southwesterlies? |
title_fullStr |
Early Spring in Europe: A Result of More Dominant North-Atlantic Southwesterlies? |
title_full_unstemmed |
Early Spring in Europe: A Result of More Dominant North-Atlantic Southwesterlies? |
title_sort |
early spring in europe: a result of more dominant north-atlantic southwesterlies? |
publishDate |
2000 |
url |
http://hdl.handle.net/2060/20000097046 |
op_coverage |
Unclassified, Unlimited, Publicly available |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
CASI |
op_relation |
Document ID: 20000097046 http://hdl.handle.net/2060/20000097046 |
op_rights |
No Copyright |
_version_ |
1766126032714203136 |