Extended Abstract (172K)J12.12
The lifespan of subseasonal locally coupled anomalies
Malaquias Pena, University of Maryland, College Park, MD; and M. Cai and E. Kalnay
Using five-day average data from the NCEP/NCAR Reanalysis, we found that most of the long lasting atmospheric anomalies are locally coupled with SST anomalies. The longer lasting anomalies tend to have a cyclonic-over-cold/anticyclonic-over-warm phase relation in the extratropics, and cyclonic-over-warm/anticyclonic-over-cold in the tropics. This preferential phase relationship of the long lasting anomalies is consistent with a predominant “atmosphere-driving” situation in the extratropics and “ocean-driving” in the tropics. A similar analysis using data from a one-way interaction model, with the ocean always forcing the atmosphere is carried out to compare the results with those from the Reanalysis. The results show that the one-way interaction produces fewer long lasting anomalies in the extratropics. These differences arise mostly in “atmosphere-driving” situations, namely, cyclonic-over-cold / anticyclonic-over-warm phase relation. This suggests that ignoring the atmosphere’s feedback effect on the ocean can lead to erroneous damping of atmospheric anomalies in the extratropics and lengthening them in the tropics.
A similar analysis over land also indicates the presence of strong directional coupling between atmospheric anomalies and surface temperature anomalies with defined geographical distributions. For example, in the eastern US, there is a tendency of long-lasting anticyclonic atmospheric anomalies to overlay warm surface anomalies, but the opposite occurs on the lee of the Rockies. We will present results relating to the impact of coupling and atmospheric and surface phase relationships over land and ocean.
Joint Session 12, Subseasonal forecasting (Joint with 15th Symp. on Global Change and Climate Variations and the Symp on Forecasting the Weathe and Climate of the Atmosphere and Ocean; Room 6C)
Tuesday, 13 January 2004, 8:30 AM-5:30 PM, Room 6C
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