Physical Sciences and Mathematics Commons^™

Observed Change In Sahel Rainfall, Circulations, African Easterly Waves, And Atlantic Hurricanes Since 1979, Shih-Yu (Simon) Wang, Robert R. Gillies

Plants, Soils, and Climate Faculty Publications

Here, we examine the dynamic properties associated with the recent increase in the Sahel rainfall using an ensemble of five global reanalysis datasets (1979–2010). The rainfall that has been observed to be increasing over the Sahel is accounted for by enhancements in both the tropical easterly jet and the African easterly jet, both of which are known to induce wet anomalies. Moreover, positional shifts in the African easterly jet and African easterly waves (AEWs) accompanied the northward migration of the Sahel rainband. Change in the African easterly jet and AEWs are coupled to a northward shift and amplification of convective …

Quasi-Decadal Spectral Peaks Of Tropical Western Pacific Ssts As A Precursor For Tropical Cyclone Threat, Shih-Yu (Simon) Wang, Adam J. Clark

Plants, Soils, and Climate Faculty Publications

A recent study identified significant spectral peaks in sea surface temperatures (SSTs) at quasi‐decadal frequency bands, which were unique to the tropical western Pacific (TWP). Using the multitaper method for spectral and coherence analysis, this study finds that the TWP SSTs at these quasi‐decadal time scales are coherent with western Pacific tropical cyclone threat [as measured by the power dissipation index (PDI)], but that the PDI lags TWP SSTs by about two years. Thus, the quasi‐decadal peaks in TWP SSTs may be a precursor for enhanced tropical cyclone threat two years later. Composite analyses are shown to illustrate how areal …

Nam Model Forecasts Of Warm Season Quasi-Stationary Frontal Environments In The Central U.S., Shih-Yu (Simon) Wang, Adam J. Clark

Plants, Soils, and Climate Faculty Publications

Using a composite procedure, North American Mesoscale Model (NAM) forecast and observed environments associated with zonally oriented, quasi-stationary surface fronts for 64 cases during July–August 2006–08 were examined for a large region encompassing the central United States. NAM adequately simulated the general synoptic features associated with the frontal environments (e.g., patterns in the low-level wind fields) as well as the positions of the fronts. However, kinematic fields important to frontogenesis such as horizontal deformation and convergence were overpredicted. Surface-based convective available potential energy (CAPE) and precipitable water were also overpredicted, which was likely related to the overprediction of the kinematic …

Atmospheric Scale Interaction On Wintertime Intermountain West Low-Level Inversions, Robert R. Gillies, Shih-Yu (Simon) Wang, Marty R. Booth

Plants, Soils, and Climate Faculty Publications

Persistent winter inversions result in poor air quality in the Intermountain West of the United States. Although the onset of an inversion is relatively easy to predict, the duration and the subsequent breakup of a persistent inversion event remains a forecasting challenge. For this reason and for this region, historic soundings were analyzed for Salt Lake City, Utah, with reanalysis and station data to investigate how persistent inversion events are modulated by synoptic and intraseasonal variabilities. The results point to a close linkage between persistent inversions and the dominant intraseasonal (30 day) mode that characterizes the winter circulation regime over …

Cfs Prediction Of Winter Persistent Inversions In The Intermountain Region, Robert R. Gillies, Shih-Yu (Simon) Wang, Jin Ho Yoon, Scott Weaver

Plants, Soils, and Climate Faculty Publications

A recent study by Gillies and others of persistent inversion events in the Intermountain West of the United States found a substantive linkage between the intraseasonal oscillation (ISO) and the development of persistent inversion events. Given that NCEP’s Climate Forecast System (CFS) has demonstrated skill in the prediction of the ISO as far out as 1 month, it was decided to examine the CFS forecast’s capability in the prediction of such winter persistent inversions. After initial analysis, a simple regression scheme is proposed that is coupled to the CFS output of geopotential height as a way to predict the occurrence …

A Planetary-Scale Land–Sea Breeze Circulation In East Asia And The Western North Pacific, W. R. Huang, J. C-L Chan, Shih-Yu (Simon) Wang

Plants, Soils, and Climate Faculty Publications

The diurnal wind variation over the East Asian continent is commonly considered to be a combination of a land-sea breeze near the coast and a mountain–valley breeze along the slopes of the Tibetan Plateau. The local land–sea breeze along the coastline typically spansHowever, a detailed examination of the global reanalysis data suggests that this local land–sea breeze circulation apparently couples with the global-scale diurnal atmospheric pressure tide to produce a planetary-scale land–sea breeze with a spatial scale of ∼1000 km over the western North Pacific. Computations of the momentum budget and equivalent potential temperatures indicate that the atmospheric diurnal tidal …

Coherence Between The Great Salt Lake Level And The Pacific Quasi-Decadal Oscillation, Shih-Yu (Simon) Wang, Robert R. Gillies, Jiming Jin, Lawrence E. Hipps

Plants, Soils, and Climate Faculty Publications

The lake level elevation of the Great Salt Lake (GSL), a large closed basin lake in the arid western United States, is characterized by a pronounced quasi-decadal oscillation (QDO).The variation of the GSL elevation is very coherent with the QDO of sea surface temperature anomalies in the tropical central Pacific (also known as the Pacific QDO). However, such coherence denies any direct association between the precipitation in the GSL watershed and the Pacific QDO because, in a given frequency, the precipitation variation always leads the GSL elevation variation. Therefore, the precipitation variation is phase shifted from the Pacific QDO. This …

Sudden Surface Warming/Drying Events Caused By Typhoon Passages Across Taiwan, T. C. Chen, Shih-Yu (Simon) Wang, M. C. Yen, A. J. Clark, J. D. Tsay

Plants, Soils, and Climate Faculty Publications

Typhoon passages across Taiwan can generate sudden surface warming in downslope regions. Special characteristics and mechanisms for 54 such warming events that were identified during the 1961–2007 period are examined. Preferred warming regions were identified in northwest Taiwan, where warming is generated by downslope flow from east or northeast winds in westward-moving typhoons, and in southeast Taiwan, where it is generated by downslope flow from west or northwest winds in northwestward-moving typhoons. In addition to the orographic effect, warmings occurred exclusively within nonprecipitation zones of typhoons. Most northwest (southeast) warmings occur during the day (night) with an average lifetime of …

A Transition-Phase Teleconnection Of The Pacific Quasi-Decadal Oscillation, Shih-Yu (Simon) Wang, R. R. Gillies, L. E. Hipps, J. Jin

Plants, Soils, and Climate Faculty Publications

The atmospheric circulation patterns associated with the Pacific quasi-decadal oscillation (QDO) are investigated using available observational data from 1948 to 2007. Previous studies indicate that the Pacific QDO is characterized by a distinct lifecycle in the form of sea surface temperature (SST) patterns. In the warm and cool phases of the Pacific QDO, the SST patterns resemble those associated with the El Niño-Southern Oscillation (ENSO). During the warm–cool and cool–warm transitions of the Pacific QDO, recurrent SST patterns are also clearly visible. The rotated empirical orthogonal function analysis on the 10–15 year filtered data shows that the evolutions of SST …

Utah Climate And Water Report, U.S. Natural Resources Conservation Service

Water

Provides a snapshot of current and immediate past climatic conditions and other information useful to agricultural and water user interests in Utah.

Evaluations Of Nam Forecasts On Midtropospheric Perturbation-Induced Convective Storms Over The U.S. Northern Plains, Shih-Yu (Simon) Wang, T. C. Chen, S. E. Taylor

Plants, Soils, and Climate Faculty Publications

In the U.S. northern plains, summer progressive convective storms that occur in weakly forced environ- ments are often coupled with short-wave perturbations that are embedded in the midlevel northwesterly flow. These midtropospheric perturbations (MPs) are capable of inducing propagating convection that contributes to a majority of the rainfall over the northern plains during July and August. There is a possibility that the difficulties of numerical weather prediction models in forecasting summer convective rainfall over the northern plains are partly attributed to their deficiency in forecasting MPs. The present study tests this possibility through examining operational forecasts by the North American …

Wind Climatology At 87 Km Above The Rocky Mountains At Bear Lake Observatory--Fabry-Perot Observations Of Oh, V. B. Wickwar, I K. Monson, C M. Vadnais, D Rees

Reports

This paper presents the neutral -wind climatology at approximately 87-km 53 altitude from Utah State University's Bear Lake Observatory (BLO). a mid-latitude site 54 situated in the middle of the Rocky Mountains. The winds were determined using a very 55 sensitive Fabry-Perot interferometer (FPI) observing the OH Me inel (6-2) PI (3) line al 56 843 nm. The climatology. determined from monthly averages of the nightly evolution of 57 the geographic meridional and zonal wind components over forty· five months, has three 58 distinct seasonal patterns: winter (November- February), summer (May-Jul y), and late 59 Slimmer (August and September). The …

Potential Regional Impacts Of Global Warming On Precipitation In The Western United States, United States Department Of The Interior, Bureau Of Reclamation

Meterology

Snow and melting of the snowpack provide the principal supply of water to much of the Western United States. Whether global warming threatens this water supply is the focus of this research. This study builds upon a previous Global Climate Change Response Program investigation. Charts were generated of four geopotential height parameters for a domain covering the eastern North Pacific Ocean and western North America. Out of 131 total winter months (from 1946-89), 35 were selected as analogues.

Monthly mean precipitation values for areas in western Montana, northern Utah, and east central Arizona were compared with median values for the …

Initial Climate Change Scenario For The Western United States, United States Department Of The Interior, Bureau Of Reclamation

Meterology

Observations of atmospheric carbon dioxide (CO₂) concentrations in recent decades have shown an accelerating upward trend due mainly to burning of fossil fuels. Physical considerations indicate that observed and projected increases in the concentrations of CO₂ and other greenhouse gases in the atmosphere will lead to significant global warming. Previous authors have followed both empirical and theoretical approaches to develop scenarios for changed climate conditions. The most common empirical approach is the use of analogs of global warming drawn from historical records and paleoclimates. The principal theoretical approach involves the interpretation of output for general circulation models …

Bulletin No. 47 - The Climate Of Utah, James Dryden

UAES Bulletins

In reporting the meteorological observations of the Station for the years 1895 and 1896, it has been thought well to include for purposes of comparison records of temperature and precipitation at several other Utah points, as well as other data of climatological importance. The bringing together of all the known facts of our climate is a work of necessity that has been too long neglected. Observers have been patiently collecting data, some of them for a quarter of a century or more, and of the mass that has been collected very little is known outside of the periodical records of …