Relationships between winter atmospheric circulation patterns and extreme tree growth anomalies in the Sierra Nevada

Tree-ring data from id-elevation (~2000 m) giant sequoia (Sequoiadendron giganteum) and high elevation (~3500 m) pines (Pinus balfouriana, Pinus albicaulis) were used to select extreme growth years from which temperature, precipitation and large-scale winter (November-Marsh, NM) 500 mn 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 northern Pacific Ocean and a tendency for southwesterly flow 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 California during these winters. NM atmospheric circulation patterns associated with extreme low growth in the pines exhibit maximum 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 of temperature and precipitation, synoptic dendroclimatological studies such as this one provide useful insights about atmospheric circulation.