The changing influences of the AMO and PDO on the decadal variation of the Santa Ana winds

Abstract

Santa Ana wind (SAW) events have great implications for the environment of Southern California, but the cause of their decadal variability has not been fully understood. We show with observational analysis that the Atlantic multi-decadal oscillation (AMO) has a stronger influence than the Pacific decadal oscillation (PDO) in modulating SAW activity through two mechanisms: the Great Basin pressure gradient mechanism, in which a strengthened Great Basin high promotes SAW activity and vice versa through the northeast-southwest pressure gradient across Southern California, and the Pacific jetstream displacement mechanism, in which a strengthened Pacific subtropical high (PSH) prohibits mid-latitude cyclones from traveling toward California, consequently encouraging SAW development and vice versa. While the AMO strengthens or weakens both the Great Basin and PSHs to strongly modulate SAW activity through these two mechanisms, the PDO strengthens one of the highs but weakens the other, causing the two mechanisms to cancel each other, producing little influence on SAW activity. A projection based on the AMO and PDO indicates that the above-average SAW activity observed since the beginning of the 21st century is likely to terminate after 2016, after which Southern California may experience an extended period of below-average SAW activity through

Future projections of wind patterns in California with the variable-resolution CESM: a clustering analysis approach

“…The second largest change in cluster frequency for the SC domain occurs in cluster 6, which is 2.3% less frequent by end-of-century. The synoptic fields for these days is depicted in Figure 11, and corresponds to a typical wind pattern from Santa Ana events (Raphael, 2003;Westerling et al, 2004;Li et al, 2016;Millstein et al, 2019;Guzman-Morales and Gershunov, 2019). The relatively high 700hPa geopotential height field over the western US, along with the high center sitting off-shore, leads to the northeasterly wind field throughout the SC region.…”

Climatology of diablo winds in Northern California and their relationships with large-scale climate variabilities

“…The red-ish colors represent higher wind speeds and lower RH, while blue-ish colors represent lower wind speeds and higher RH controls the low-level wind patterns over SFBA. Second, they can modulate the latitudinal location of the 350-hPa Pacific jet stream, which steers the path of winter cyclones and atmospheric rivers (ARs) (Li et al 2016;Liu et al 2018;Raphael and Mills 1996). The former will be referred to as the pressure anomaly mechanism, while the latter will be referred to as the jet stream displacement mechanism.…”

“…The DWs, which are a type of downslope wind, are characterized as warm, dry, and gusty northerly to northeasterly winds. They occur most frequently during the fall to early winter from the Northern Coast Ranges into the SFBA, and down the western slopes of the Sierra Nevada Mountain Range into the Great Central Valley (Li et al 2016). Occurrences of DWs are often associated with near-surface ridges that settle either along the coast of Oregon and Washington and/or over the Great Basin (Abatzoglou et al 2013;Brewer and Clements 2020;Hughes and Hall 2010;Mass and Ovens 2019), which feature a stable low-level atmosphere.…”

“…Despite DWs' strong linkage to ignition and spread of destructive wildfires in Northern California, there have been very limited studies dedicated to the DWs, especially when compared to the Santa Ana Winds (SAWs) in Southern California (Abatzoglou et al 2013;Guzman-Morales and Gershunov 2019;Guzman-Morales et al 2016;Hughes and Hall 2010;Jones et al 2010;Li et al 2016;Monteverdi 1973;Rolinski et al 2019). A long-term climatology study on DWs is still lacking and their relations with large-scale climate variabilities have not been elucidated.…”

Five-century record of climate and groundwater recharge variability in southern California

“…In southern California, positive phases of the PDO Index are associated with higher precipitation and vice versa 22 . In this region, past studies identified the influence of the PDO on precipitation 12,24 , streamflow 13 , lake levels 25 , wind 26 , and water levels in groundwater wells 12,13 .…”