scholarly journals Seasonal Variation and Spatial Patterns of the Atmospheric Component of the Pacific Decadal Oscillation

2013 ◽  
Vol 26 (5) ◽  
pp. 1575-1594 ◽  
Author(s):  
Catrin M. Mills ◽  
John E. Walsh
Keyword(s):  
United States ◽  
North America ◽  
Air Temperature ◽  
Pacific Decadal Oscillation ◽  
Southern Oscillation ◽  
Grid Point ◽  
Southeastern United States ◽  
Surface Air Temperature ◽  
The Pacific ◽  
Difference Fields

Abstract The Pacific decadal oscillation (PDO) is an El Niño–Southern Oscillation (ENSO)-like climate oscillation that varies on multidecadal and higher-frequency scales, with a sea surface temperature (SST) dipole in the Pacific. This study addresses the seasonality, vertical structure, and across-variable relationships of the local North Pacific and downstream North American atmospheric signal of the PDO. The PDO-based composite difference fields of 500-mb geopotential height, surface air temperature, sea level pressure, and precipitation vary not only across seasons, but also from one calendar month to another within a season, although month-to-month continuity is apparent. The most significant signals occur in western North America and in the southeastern United States, where a positive PDO is associated with negative heights, consistent with underlying temperatures in the winter. In summer, a negative precipitation signal in the southeastern United States associated with a positive PDO phase is consistent with a ridge over the region. When an annual harmonic is fit to the 12 monthly surface air temperature differences at each grid point, the PDO temperature signal peaks in winter in most of North America, while a peak in summer occurs in the southeastern United States. Approximately 25% of the variance of the PDO index is accounted for by ENSO. Atmospheric composite differences based on a residual (ENSO linearly removed) PDO index have many similarities to those of the full PDO signal.

scholarly journals The Interannual Variability of the Haines Index over North America

2013 ◽  
Vol 52 (11) ◽  
pp. 2396-2409 ◽  
Author(s):  
Lejiang Yu ◽  
Shiyuan Zhong ◽  
Xindi Bian ◽  
Warren E. Heilman ◽  
Joseph J. Charney
Keyword(s):  
United States ◽  
Pacific Ocean ◽  
North America ◽  
Interannual Variability ◽  
Large Scale ◽  
Southern Oscillation ◽  
Southeastern United States ◽  
Lower Atmosphere ◽  
The Arctic ◽  
Fire Weather Index

AbstractThe Haines index (HI) is a fire-weather index that is widely used as an indicator of the potential for dry, low-static-stability air in the lower atmosphere to contribute to erratic fire behavior or large fire growth. This study examines the interannual variability of HI over North America and its relationship to indicators of large-scale circulation anomalies. The results show that the first three HI empirical orthogonal function modes are related respectively to El Niño–Southern Oscillation (ENSO), the Arctic Oscillation (AO), and the interdecadal sea surface temperature variation over the tropical Pacific Ocean. During the negative ENSO phase, an anomalous ridge (trough) is evident over the western (eastern) United States, with warm/dry weather and more days with high HI values in the western and southeastern United States. During the negative phase of the AO, an anomalous trough is found over the western United States, with wet/cool weather and fewer days with high HI, while an anomalous ridge occurs over the southern United States–northern Mexico, with an increase in the number of days with high HI. After the early 1990s, the subtropical high over the eastern Pacific Ocean and the Bermuda high were strengthened by a wave train that was excited over the tropical western Pacific Ocean and resulted in warm/dry conditions over the southwestern United States and western Mexico and wet weather in the southeastern United States. The above conditions are reversed during the positive phase of ENSO and AO and before the early 1990s.

Predictable Patterns of Wintertime Surface Air Temperature in Northern Hemisphere and Their Predictability Sources in the SEAS5

2020 ◽  
Vol 33 (24) ◽  
pp. 10743-10754
Author(s):  
Hongdou Fan ◽  
Lin Wang ◽  
Yang Zhang ◽  
Youmin Tang ◽  
Wansuo Duan ◽  
...  
Keyword(s):  
North America ◽  
Northern Hemisphere ◽  
Air Temperature ◽  
Southern Oscillation ◽  
Arctic Sea Ice ◽  
Prediction Skill ◽  
The Arctic ◽  
The Tibetan Plateau ◽  
Central Pacific ◽  
The Pacific

AbstractBased on 36-yr hindcasts from the fifth-generation seasonal forecast system of the European Centre for Medium-Range Weather Forecasts (SEAS5), the most predictable patterns of the wintertime 2-m air temperature (T2m) in the extratropical Northern Hemisphere are extracted via the maximum signal-to-noise (MSN) empirical orthogonal function (EOF) analysis, and their associated predictability sources are identified. The MSN EOF1 captures the warming trend that amplifies over the Arctic but misses the associated warm Arctic–cold continent pattern. The MSN EOF2 delineates a wavelike T2m pattern over the Pacific–North America region, which is rooted in the tropical forcing of the eastern Pacific-type El Niño–Southern Oscillation (ENSO). The MSN EOF3 shows a wavelike T2m pattern over the Pacific–North America region, which has an approximately 90° phase difference from that associated with MSN EOF2, and a loading center over midlatitude Eurasia. Its sources of predictability include the central Pacific-type ENSO and Eurasian snow cover. The MSN EOF4 reflects T2m variability surrounding the Tibetan Plateau, which is plausibly linked to the remote forcing of the Arctic sea ice. The information on the leading predictable patterns and their sources of predictability is further used to develop a calibration scheme to improve the prediction skill of T2m. The calibrated prediction skill in terms of the anomaly correlation coefficient improves significantly over midlatitude Eurasia in a leave-one-out cross-validation, implying a possible way to improve the wintertime T2m prediction in the SEAS5.

scholarly journals Impacts of the Madden–Julian Oscillation on Storm-Track Activity, Surface Air Temperature, and Precipitation over North America

2018 ◽  
Vol 31 (15) ◽  
pp. 6113-6134 ◽  
Author(s):  
Cheng Zheng ◽  
Edmund Kar-Man Chang ◽  
Hye-Mi Kim ◽  
Minghua Zhang ◽  
Wanqiu Wang
Keyword(s):  
United States ◽  
North America ◽  
Air Temperature ◽  
West Coast ◽  
Storm Track ◽  
Surface Air Temperature ◽  
Madden Julian Oscillation ◽  
Temperature And Precipitation ◽  
Storm Track Activity ◽  
Wave Trains

In this study, the intraseasonal variations in storm-track activity, surface air temperature, and precipitation over North America associated with the Madden–Julian oscillation (MJO) in boreal winter (November–April) are investigated. A lag composite strategy that considers different MJO phases and different lag days is developed. The results highlight regions over which the MJO has significant impacts on surface weather on intraseasonal time scales. A north–south shift of storm-track activity associated with the MJO is found over North America. The shift is consistent with the MJO-related surface air temperature anomaly over the eastern United States. In many regions over the western, central, and southeastern United States, the MJO-related precipitation signal is also consistent with nearby storm-track activity. An MJO-related north–south shift of precipitation is also found near the west coast of North America, with the precipitation over California being consistent with the MJO-related storm-track activity over the eastern Pacific. MJO-related temperature and storm-track anomalies are also found near Alaska. Further analyses of streamfunction anomalies and wave activity flux show clear signatures of Rossby wave trains excited by convection anomalies related to MJO phases 3 and 8. These wave trains propagate across the Pacific and North America, bringing an anticyclonic (cyclonic) anomaly to the eastern part of North America, shifting the westerly jet to the north (south), thereby modulating the surface air temperature and storm-track activity over the continent. Rossby waves associated with phases 2 and 6 are also found to impact the U.S. West Coast.

Comparisons of different definitions of the western Pacific pattern and associated winter climate anomalies in Eurasia and North America

2020 ◽  
Author(s):  
Hasi Aru
Keyword(s):  
North America ◽  
Air Temperature ◽  
Southern Oscillation ◽  
Surface Air Temperature ◽  
Western Pacific ◽  
The Arctic ◽  
Temperature Anomalies ◽  
The Western Pacific ◽  
Air Temperature Anomalies ◽  
Western Pacific Pattern

<p>The western Pacific pattern (WP) is one of the most prominent teleconnection patterns over the Northern Hemisphere (NH) in boreal winter. There exist several methods employed to identify the WP in the literature. This study compares eight WPs defined by different methods. Correlation coefficients among the eight WP indices (WPIs) show considerable spreads, though most of them are statistically significant. The meridional dipole structure of WP can be captured by all of the WPIs, but it shows large spreads in the locations of the centers. Several WPIs produce a significant correlation with the winter Arctic Oscillation, with marked signals of atmospheric anomalies over the Arctic region. Connections of the WPs with the simultaneous winter El Niño-Southern Oscillation (ENSO) depend largely upon their definitions. Impacts of the WPs on the surface air temperature over many parts of Eurasia and North America are also sensitive to their definitions. Differences in the surface air temperature anomalies are closely related to differences in the spatial structure of the WPs. Finally, we define a new WP index as differences in the area-average 500-hPa geopotential height anomalies between subtropics and mid-latitude of northwestern Pacific. This newly defined WP index has a close relation with the above eight WPIs, the tropical Pacific sea surface temperature and surface air temperature anomalies over Eurasia and North America.</p>

Diagnosing Sources of U.S. Seasonal Forecast Skill

2006 ◽  
Vol 19 (13) ◽  
pp. 3279-3293 ◽  
Author(s):  
X. Quan ◽  
M. Hoerling ◽  
J. Whitaker ◽  
G. Bates ◽  
T. Xu
Keyword(s):  
Air Temperature ◽  
Southern Oscillation ◽  
Surface Air Temperature ◽  
Seasonal Forecast ◽  
Forecast Skill ◽  
Diagnostic Methods ◽  
Sea Surface ◽  
Empirical Methods ◽  
Spatial Coverage ◽  
Sst Anomalies

Abstract In this study the authors diagnose the sources for the contiguous U.S. seasonal forecast skill that are related to sea surface temperature (SST) variations using a combination of dynamical and empirical methods. The dynamical methods include ensemble simulations with four atmospheric general circulation models (AGCMs) forced by observed monthly global SSTs from 1950 to 1999, and ensemble AGCM experiments forced by idealized SST anomalies. The empirical methods involve a suite of reductions of the AGCM simulations. These include uni- and multivariate regression models that encapsulate the simultaneous and one-season lag linear connections between seasonal mean tropical SST anomalies and U.S. precipitation and surface air temperature. Nearly all of the AGCM skill in U.S. precipitation and surface air temperature, arising from global SST influences, can be explained by a single degree of freedom in the tropical SST field—that associated with the linear atmospheric signal of El Niño–Southern Oscillation (ENSO). The results support previous findings regarding the preeminence of ENSO as a U.S. skill source. The diagnostic methods used here exposed another skill source that appeared to be of non-ENSO origins. In late autumn, when the AGCM simulation skill of U.S. temperatures peaked in absolute value and in spatial coverage, the majority of that originated from SST variability in the subtropical west Pacific Ocean and the South China Sea. Hindcast experiments were performed for 1950–99 that revealed most of the simulation skill of the U.S. seasonal climate to be recoverable at one-season lag. The skill attributable to the AGCMs was shown to achieve parity with that attributable to empirical models derived purely from observational data. The diagnostics promote the interpretation that only limited advances in U.S. seasonal prediction skill should be expected from methods seeking to capitalize on sea surface predictors alone, and that advances that may occur in future decades could be readily masked by inherent multidecadal fluctuations in skill of coupled ocean–atmosphere systems.

An Updated Climatology of Tropical Cyclone Impacts on the Southwestern United States

2013 ◽  
Vol 141 (12) ◽  
pp. 4322-4336 ◽  
Author(s):  
Kimberly M. Wood ◽  
Elizabeth A. Ritchie
Keyword(s):  
United States ◽  
North Pacific ◽  
General Circulation ◽  
Southern Oscillation ◽  
Eof Analysis ◽  
Southwestern United States ◽  
Oscillation Phenomenon ◽  
The Pacific ◽  
Sea Surface Temperature Anomalies ◽  
Significant Patterns

Abstract A dataset of 167 eastern North Pacific tropical cyclones (TCs) is investigated for potential impacts in the southwestern United States over the period 1989–2009 and evaluated in the context of a 30-yr climatology. The statistically significant patterns from empirical orthogonal function (EOF) analysis demonstrate the prevalence of a midlatitude trough pattern when TC-related rainfall occurs in the southwestern United States. Conversely, the presence of a strong subtropical ridge tends to prevent such events from occurring and limits TC-related rainfall to Mexico. These statistically significant patterns correspond well with previous work. The El Niño–Southern Oscillation phenomenon is shown to have some effect on eastern North Pacific TC impacts on the southwestern United States, as shifts in the general circulation can subsequently influence which regions receive rainfall from TCs or their remnants. The Pacific decadal oscillation may have a greater influence during the period of study as evidenced by EOF analysis of sea surface temperature anomalies.

scholarly journals Progression of Sugarberry (Celtis laevigata) Dieback and Mortality in the Southeastern United States

2021 ◽  
Author(s):  
Emilee M Poole ◽  
Michael D Ulyshen ◽  
Scott Horn ◽  
Patrick Anderson ◽  
Chip Bates ◽  
...  
Keyword(s):  
United States ◽  
North America ◽  
Invasive Plants ◽  
Southeastern United States ◽  
Public Spaces ◽  
Canopy Gaps ◽  
Leaf Fall ◽  
Affected Area ◽  
Celtis Laevigata ◽  
Branch Dieback

Abstract The southeastern United States has been experiencing unexplained sugarberry (Celtis laevigata) mortality for over a decade, representing one of the most severe and widespread Celtis mortality episodes ever reported from North America. Here we describe external symptoms, progression of mortality, and the known geographic extent of the problem. More than half of all trees monitored at one site within the affected area died over five years of observation. Although many trees died within a year of first exhibiting symptoms (e.g., small yellow leaves, branch dieback, premature leaf fall), many others continued living for years after becoming symptomatic. A preliminary insecticide trial found no improvements in survivorship among trees treated with insecticides, emamectin benzoate and imidacloprid, relative to control trees. Our findings suggest the problem will likely continue and become more widespread in the coming years. Study Implications Sugarberry mortality in urban and forested environments is an ongoing problem that has the potential to spread throughout the southeastern United States and perhaps more widely, depending on the susceptibility of other native Celtis species. Many trees die within a year of first showing external symptoms, whereas others can live for many years after appearing symptomatic. Declining trees in rights-of-way and public spaces are presenting costly hazards to cities, and canopy gaps in natural areas are likely to facilitate the establishment and spread of invasive plants. Studies aimed at determining the cause of this problem are urgently needed.

Do centers of origin have a center?

Paleobiology ◽  
1981 ◽  
Vol 7 (3) ◽  
pp. 305-307 ◽  
Author(s):  
John C. Briggs
Keyword(s):  
United States ◽  
North America ◽  
Southeastern United States ◽  
Important Criterion ◽  
Centers Of Origin ◽  
Single Region ◽  
Evolutionary Radiation ◽  
A Current ◽  
Considerable Intensity

A current question being debated with considerable intensity is whether or not certain geographic areas act as centers of evolutionary radiation and supply species to other areas that are less active or less effective in an evolutionary sense. Darwin (1859) was the first to write about centers of origin which he called “single centers of creation.” He argued that each species was first produced within a single region and that it subsequently migrated from that area as far as its powers of migration and subsistence under past and present conditions permitted. Adams (1902), in discussing the influence of the southeastern United States as a center of distribution for the flora and fauna of North America, provided a series of criteria for the determination of “centers of dispersal.” His first, and evidently most important criterion was the location of “the greatest differentiation of a type.”

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