ABSTRACT: Relationships between winter atmospheric circulation patterns and extreme tree growth anomalies in the SierraNevada

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Abstract

Tree-ring data from mid-elevation (similar to 2000 m) giant sequoia (Sequoiadendron giganteum) and high elevation (similar to 3500 m) pines (Pinus balfouriana, Pinus albicaulis) were used to select extreme growth years from which temperature, precipitation and large-scale winter (November- March, NM) 500 mb circulation patterns associated with the extreme tree growth anomalies were examined.Winters preceding extreme high growth in both giant sequoia and pines are warm and wet and are characterized by anomalous low pressure in the northeastern Pacific Ocean and a tendency for southwesterly flow and advection of warm maritime air into California. For the pines, such winters exhibit a pattern of anomalous low pressure in the northern Pacific, anomalous high pressure over northwestern Canada and anomalous low pressure across the southern US. NM 500 mb heights suggest more meridional circulation during the warm and dry winters preceding extreme low growth in giant sequoia. Atmospheric circulation during these winters exhibits a persistent trough/ridge pattern between the central Pacific and the western US. Storms are deflected away from Californiaduring these winters. NM atmospheric circulation patterns associated with extreme low growth in the pines exhibitmaximum westerlies north of their mean position and the tendency for enhanced ridging in the northeast Pacific, which advects cool dry air into the Sierra Nevada.As dendroclimatic reconstructions are more frequently employed in order to better understand past variability oftemperature and precipitation, synoptic dendroclimatological studies such as this one provide useful insightsabout atmospheric circulation. (C) 1998 Royal Meteorological Society.

Bibliography of Canadian Geomorphology