Environmental Factors Controlling the Precipitation in California

Feng Hu,Qiao Liu,Dorina Chyi,Leying Zhang

doi:10.3390/atmos12080997

Abstract

Using observational data covering 1948–2020, the environmental factors controlling the winter precipitation in California were investigated. Empirical orthogonal function (EOF) analysis was applied to identify the dominant climate regimes contributing to the precipitation. The first EOF mode described a consistent change, with 70.1% variance contribution, and the second mode exhibited a south–east dipole change, with 11.7% contribution. For EOF1, the relationship was positive between PC1(principal component) and SST (sea surface temperature) in the central Pacific Ocean, while it was negative with SST in the southeast Indian Ocean. The Pacific–North America mode, induced by the positive SST and precipitation in the central Pacific Ocean, leads to California being occupied by southwesterlies, which would transport warm and wet flow from the ocean, beneficial for precipitation. As for the negative relationship, California is controlled by biotrophically high pressure, representing part of the Rossby wave train induced by the positive SST in the Indian ocean, which is unfavorable for the precipitation. For EOF2, California is controlled by positive vorticity at the upper level, whereas at the lower level, there is positive vorticity to the south and negative vorticity to the north, the combination of which leads to the dipole mode change in the precipitation.

Highlights

The state of California is the largest agricultural producer of the United States (US) and one of the major agricultural areas of the world [1,2]
In the north of California, there is negative vorticity, which is unfavorable for precipitation
Considering the seasonal mean and standard deviation of precipitation, this paper focused on winter as the main rainy season with the greatest variation

Summary

Introduction

The state of California is the largest agricultural producer of the United States (US) and one of the major agricultural areas of the world [1,2]. Global warming caused by human activities accounts for 5–18% of the abnormal droughts, natural variability is still the main controlling factor for the precipitation anomaly [10,11]. A number of previous studies has investigated the precipitation in summer in the US They proposed that convective heating over the subtropical western Pacific Ocean could induce a wave train pattern, which spans the northern Pacific Ocean and North America, affecting US precipitation [12,13,14]. The objective of the current study was to investigate the environmental factors controlling precipitation in the winter in California. The EOF method allows for the decomposition of the original three-dimensional variable field into orthogonal spatial modes and time series, Atmosphere 2021, 12, 997 so that each mode contains the specific information of the original field. Only the first two leading EOF modes were considered

Regression Analysis

Anomaly General Circulation Model

Basic Evolution of Precipitation

Summary and Discussion