HR: 13:50h
AN: A53E-02    [Abstracts]
TI: Temporal and Spatial Changes in Northern Hemisphere Floating Climatological Seasons
AU: * Choi, G
EM: tribute@hanmail.net
AF: Rutgers University, Department of Geography 54 Joyce Kilmer Avenue, Piscataway, NJ 08854, United States
AU: Robinson, D A
EM: drobins@rci.rutgers.edu
AF: Rutgers University, Department of Geography 54 Joyce Kilmer Avenue, Piscataway, NJ 08854, United States
AB: Floating climatological seasons, for which onsets and durations vary temporally and spatially, are examined over Northern Hemisphere continents and oceans. Among the variables evaluated are surface air temperature, snow extent, vegetation greenness, and atmospheric carbon dioxide concentrations. Seasonal thresholds are defined for each variable (e.g. daily mean temperature exceeding 5°C (20°C) to mark the beginning of spring (summer)). The dates on which these thresholds are reached at a given location are determined for each year over the past three decades. These seasonal onsets and offsets "float" temporally and spatially from year to another. An analysis of floating dates finds that winter duration has shortened in Europe, eastern Asia, and western North America, primarily due to an earlier spring onset. The spatial pattern of this earlier onset is associated with a positive Arctic Oscillation (AO) regime in the previous winter months. The positive winter AO finds anomalously high pressure sitting in the middle latitudes in locations where spring arrives early. This is likely due to a combination of advective fluxes of warmth and moisture and the local enhancement of solar radiation reaching the surface under clear skies. This, in turn, promotes earlier snow melt that further enhances warming and an earlier green-up. Extended summer duration is observed over continents and oceans (except the Arctic Ocean, where summer does not exist). The oceanic zone along 30°N has experienced a particularly large increase in duration, suggesting Hadley cell expansion.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting