Séminaire
Extreme hot days as defined for the California central valley (CV) have a characteristic large scale structure that affects much of the west coast of North America as well. Extreme cold air outbreaks affect much of the southwestern United States. The patterns for both types of extreme events (EEs) will be briefly summarized, including statistically highly significant regions far from California. Simple statistics (boostrap resampling and simple tail tests) for assigning significance to parts of the EE patterns in both cases will be summarized.
The EE patterns for the hottest 1% of summer days have been compared to daily weather maps in a simple calculation of a daily anomaly 'HDA index' to hindcast (and forecast) hottest days in daily anomaly values. The 'HDA index' captures ~1/2 of the hottest 1% days from a 25 year period using a peaks over a threshold test to find the highest 1% of HDA index and CV observed temperature. Perhaps unexpectedly, the HDA index has high correlation with maximum temperatures on near-normal and below-normal dates as well (overall correlation between daily maximum temperature at central valley stations and HDA index: 0.84).
Remaining questions include how the large scale patterns develop dynamically and improved extreme statistics.
Riwal Plougonven,
Laboratoire de Météorologie Dynamique - ENS,
24 rue Lhomond, 75005 Paris,
tel: 01 44 32 27 31