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Hawaiian Winter Rainfall Variability during Central Pacific (CP) and Eastern Pacific (EP) El Niño Events.

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Title:Hawaiian Winter Rainfall Variability during Central Pacific (CP) and Eastern Pacific (EP) El Niño Events.
Authors:Bai, Xiaoyu
Contributors:Atmospheric Sciences (department)
Date Issued:Aug 2017
Publisher:University of Hawaiʻi at Mānoa
Abstract:Historically, Hawaiian winter (December through February) rainfall is known to be drierthan-
normal during El Ni~no events due to the eastward shift in the subtropical jet stream
core over the North Paci c and enhanced sinking motion associated with the local Hadley
circulation over the central Paci c. Recent studies suggest that El Ni~no can be broadly
separated into two types: (1) Eastern Paci c (EP) El Ni~no which has its largest sea surface
temperature (SST) anomalies centered in the equatorial eastern Paci c, and (2) Central
Paci c (CP) El Ni~no which has its largest SST anomalies centered in the equatorial central
Paci c. When considering El Ni~no events according to these two types, is Hawaiian winter
rainfall still drier-than-normal?
This study rst compares precipitation records between 1957 to present of 21 stations
from Kauai, Oahu, Maui and Hawaii during the two types of El Ni~no winters. Results show
that all stations are wetter during CP winters than EP winters. Comparison between EP, CP
winters and climatology shows that during EP El Ni~no winters the Hawaiian Islands have a
drier-than-normal precipitation pattern, while during CP El Ni~no winters the Hawaiian Islands
have a normal precipitation distribution and, for some stations, slightly wetter-than-normal
precipitation anomalies. To nd the mechanisms behind these rainfall anomalies during CP
and EP winters, further analysis is on the subtropical jet stream, horizontal wind eld, vertical
velocity, outgoing longwave radiation, speci c humidity, and moisture transport. Dynamical
downscaling using Advanced Research Weather Research and Forecasting (WRF-ARW) model
is adopted to show a detailed wind eld distribution and rainfall simulation. The Hawaiian
Rainfall Atlas, which is a set of high resolution Hawaiian rainfall maps, is also analyzed to
show spatial rainfall anomalies during the two types of El Ni~no.
Although more research needs to be done, the hypothetical contributions to the wetter
conditions on the Hawaiian Islands during CP winters as compared to EP winters are: lower
level southwesterly wind anomalies, weaker descending motion over the Islands, and positive
speci c humidity anomalies over the Islands.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2017.
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Atmospheric Sciences

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