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| Titel |
The influence of solar wind on extratropical cyclones – Part 2: A link mediated by auroral atmospheric gravity waves? |
| VerfasserIn |
P. Prikryl, D. B. Muldrew, G. J. Sofko |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 27, no. 1 ; Nr. 27, no. 1 (2009-01-06), S.31-57 |
| Datensatznummer |
250016354
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| Publikation (Nr.) |
 copernicus.org/angeo-27-31-2009.pdf |
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| Zusammenfassung |
| Cases of mesoscale cloud bands in extratropical cyclones
are observed a few hours after atmospheric gravity waves (AGWs) are launched
from the auroral ionosphere. It is suggested that the solar-wind-generated
auroral AGWs contribute to processes that release instabilities and initiate
slantwise convection thus leading to cloud bands and growth of extratropical
cyclones. Also, if the AGWs are ducted to low latitudes, they could
influence the development of tropical cyclones. The gravity-wave-induced
vertical lift may modulate the slantwise convection by releasing the moist
symmetric instability at near-threshold conditions in the warm frontal zone
of extratropical cyclones. Latent heat release associated with the mesoscale
slantwise convection has been linked to explosive cyclogenesis and severe
weather. The circumstantial and statistical evidence of the solar wind
influence on extratropical cyclones is further supported by a statistical
analysis of high-level clouds (<440 mb) extracted from the International
Satellite Cloud Climatology Project (ISCCP) D1 dataset. A statistically
significant response of the high-level cloud area index (HCAI) to fast solar
wind from coronal holes is found in mid-to-high latitudes during
autumn-winter and in low latitudes during spring-summer. In the
extratropics, this response of the HCAI to solar wind forcing is consistent
with the effect on tropospheric vorticity found by Wilcox et al. (1974) and
verified by Prikryl et al. (2009). In the tropics, the observed HCAI
response, namely a decrease in HCAI at the arrival of solar wind stream
followed by an increase a few days later, is similar to that in the northern
and southern mid-to-high latitudes. The amplitude of the response nearly
doubles for stream interfaces associated with the interplanetary magnetic
field BZ component shifting southward. When the IMF BZ after the
stream interface shifts northward, the autumn-winter effect weakens or
shifts to lower (mid) latitudes and no statistically significant response is
found at low latitudes in spring-summer. The observed effect persists
through years of low and high volcanic aerosol loading. The similarity of
the response in mid-to-high and low latitudes, the lack of dependence upon
aerosol loading, and the enhanced amplitude of the effect when IMF BZ
component shifts southward, favor the proposed AGW link over the atmospheric
electric circuit (AEC) mechanism (Tinsley et al., 1994). The latter requires
the presence of stratospheric aerosols for a significant effect and should
produce negative and positive cloud anomalies in mid-to-high and low
latitudes, respectively. However, if the requirement of aerosols for the AEC
mechanism can be relaxed, the AGW and AEC mechanisms should work in synergy
at least in mid-to-high latitudes. |
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