Role of Multiple-Level Tropospheric Circulations in Forcing ENSO Winter Precipitation Anomalies

Abstract

Regionally organized winter (DJF) precipitation anomalies over North America are presented in association with cold and warm phases of the ~ Nifio-Southern Oscillation. Variations in low-level flow from moisture sources aDd in upper-level dynamic properties are diagnosed for eKb anomalous precipitation region using DJF composites of upper-and lower-tropospheric winds. sea level pressure. divergence, and vorticity advection. Variance analysis determines which precipitation and circulation patterns are robust and evaluates the predictability of the extreme phase composites with respect to the climatology. In cold phases. the P-=ific Northwest aDd the lower Mississippi Valley regions have above-nonnal precipitation tOtals. The heavier precipitation over the Pacific Northwest is the result of a multilevel onshore flow forced by an amplified Pacific high off the California coast and a single zonal upper-tropospheric jet. In the Lower Mississippi and Tennessee Valleys, the equatorward entrance region of a west-east-oriented jet core combines with anomalous positive vorticity advection (pV A) and a convergent low-level flow off the Gulf of Mexico. resulting in heavier precipitation. Drier than nonnal conditions occur in coastal Aluka aDd California due to negative vorticity advection anomalies aloft, low-level divergence. and weaker onshore ftow. The increased precipitation over the southern Mississippi Valley and the Pacific Northwest, and the drier conditions over Florida. are statistically robust. During warm phases. more precipitation occurs in the coastal regions of Alaska. California, aDd the Gulf of Mexico, whereas drier conditions persist over the Pacific Northwest. Alaskan precipitation is enhanced by strong. convergent. onshore ftow associated with a deeper Aleutian low. upper-level PV A. aDd the northern branch of a split jet pattern. A strong southern subtropical branch of the split jet provides dynamic support for uplift of moisture along the Gulf Coast. The drier conditions in the Pacific Northwest and the wet conditions in Texas aDd Florida are predictable relative to the climatology and are statistically robust.

Lagged relationships between North American snow mass and atmospheric teleconnection indices

“…This study complements earlier research into atmospheric circulation and winter climate over North America (Barton and Ramirez, 2004;Cayan, 1996;Coleman and Rogers, 2003;Serreze et al, 1998;Smith et al, 1998). A new association is suggested between preceding season PDO and winter SWE over the eastern portion of the continent.…”

Variability of Winter Storminess in the Eastern United States during the Twentieth Century from Tide Gauges

“…Their results are consistent with others who found similar relationships between ENSO phase and storm activity in the region of the SOC track (Noel and Changnon 1998;Hirsch et al 2001;Schubert et al 2005). The ENSO teleconnection with storminess in the eastern United States occurs via strengthening of the southern branch of the jet stream over North America (Smith et al 1998) and an increase in sea surface temperature in the GOM and southeastern U.S. coastal regions (DeGaetano et al 2002). Despite the advantages of modern meteorological products, they are not suitable for analyses of multidecadal variability in storminess, because they are limited temporally to the second half of the twentieth century.…”

Meteotsunamis in the northeastern Gulf of Mexico and their possible link to El Niño Southern Oscillation

“…Previous studies have shown that the frequency and intensity of tropical cyclones and winter cold fronts in this area are affected by climate variability. For example, Eichler and Higgins (2006) found Gulf of Mexico cyclogenesis occurred more often during the warm El Niño Southern Oscillation (ENSO) phase, because of strengthening of the southern branch of the jet stream over North America (Smith et al 1998) and increased sea surface temperature in the Gulf of Mexico (DeGaetano et al 2002). Thompson et al (2013) corroborated the previous findings and identified a multidecadal increase in storm frequency from early to late twentieth century along the Gulf of Mexico and over the southeastern coast.…”