scholarly journals Development of Anomalous Temperature Regimes over the Southeastern United States: Synoptic Behavior and Role of Low-Frequency Modes

2015 ◽  
Vol 30 (3) ◽  
pp. 553-570 ◽  
Author(s):  
Rebecca M. Westby ◽  
Robert X. Black
Keyword(s):  
United States ◽  
Geopotential Height ◽  
Southeastern United States ◽  
Low Frequency ◽  
Height Anomaly ◽  
Geopotential Height Anomaly ◽  
Upper Troposphere ◽  
The North ◽  
Temperature Regimes

Abstract During winter, anomalous temperature regimes (ATRs), which include cold-air outbreaks (CAOs) and warm waves (WWs), have important impacts in the southeastern United States. This study provides a synoptic–dynamic characterization of ATRs in the southeastern United States from 1949 to 2011 through composite time-evolution analyses. Events are categorized by the sign and amplitude of relevant low-frequency modes. During CAO (WW) onset, negative (positive) geopotential height anomalies are observed in the upper troposphere over the Southeast with oppositely signed anomalies in the lower troposphere over the central United States. In most cases, there is a surface east–west geopotential height anomaly dipole, with anomalous northerly (CAO) or southerly (WW) flow into the Southeast leading to cold or warm surface air temperature anomalies, respectively. Companion potential vorticity anomaly analyses reveal prominent features in the mid- to upper troposphere consistent with the coincident geopotential height anomaly patterns. Ultimately, synoptic-scale disturbances are found to serve as dynamic triggers for ATR events, while low-frequency modes provide a favorable environment for ATR onset. The results provide a qualitative indication of the role of low-frequency modes in ATR onset. In WW (CAO) events influenced by low-frequency modes, the North American geopotential height anomaly pattern arises in part as a downstream (regional) manifestation of the negative Pacific–North American pattern (North Atlantic Oscillation). Interestingly, the North Atlantic Oscillation contributes to both CAO onset and demise. Thus, these results indicate that low-frequency modes also affect event duration (CAOs). One general distinction found for ATRs is that CAOs involve substantial airmass transport while WW formation is more regional in nature.

scholarly journals The Quasi-Biweekly Oscillation of Summer Rainfall in Southern China and Its Relationship With the Geopotential Height Anomaly Over the North Atlantic Ocean

2021 ◽  
Vol 9 ◽  
Author(s):  
Qian Huang ◽  
Xinyu Yin ◽  
Suxiang Yao
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Geopotential Height ◽  
North Atlantic Ocean ◽  
Southern China ◽  
Summer Precipitation ◽  
Height Anomaly ◽  
Geopotential Height Anomaly ◽  
The North ◽  
The North Atlantic

Summer precipitation in East Asia has significant quasi-biweekly (10–30-day) oscillation characteristics. By using gauge-based precipitation and ERA-Interim reanalysis data, the basic mode of the quasi-biweekly oscillation of summer precipitation in East Asia and the related circulation from 1979 to 2012 were analyzed. It was found that the middle and lower reaches of the Yangtze River and its south in China were among the key areas for the 10- to 30-day oscillation of summer precipitation. After selecting typical summer precipitation events with 10- to 30-day oscillation characteristics in key areas and conducting composite analysis, it is found that in the dry (wet) phase of quasi-biweekly precipitation in southern China, it is controlled by quasi-biweekly anticyclone (cyclone) at 500 hPa above the key area. During the evolution of quasi-biweekly precipitation, the ridge of the Northwest Pacific Subtropical High is located between 20 and 22°N latitude, and there is no significant variability in the large-scale background circulation. Furthermore, composite analysis of the precursory signal at 500 hPa during quasi-biweekly precipitation in southern China found that there was an obvious quasi-biweekly geopotential height anomaly over the North Atlantic Ocean almost 30 days before the peak day of quasi-biweekly precipitation. While the quasi-biweekly geopotential height anomaly at 500 hPa in the North Atlantic propagates eastward, it also leads the cold air to transport southward. Cold air from high latitudes and warm air from low latitudes converge in southern China, which affects the quasi-biweekly oscillation of precipitation. Hysteresis synthesis of precipitation based on 500 hPa geopotential height’s quasi-biweekly oscillation events over the North Atlantic Ocean comes to almost the same conclusion. Therefore, the 500 hPa geopotential height quasi-biweekly anomaly in the North Atlantic may have important prediction significance for an extended-range forecast of summer rainfall in China.

scholarly journals Blocking Detection Based on Synoptic Filters

2011 ◽  
Vol 2011 ◽  
pp. 1-11 ◽  
Author(s):  
Bernd Schalge ◽  
Richard Blender ◽  
Klaus Fraedrich
Keyword(s):  
Case Studies ◽  
Southern Hemisphere ◽  
Geopotential Height ◽  
Height Anomaly ◽  
Geopotential Height Anomaly ◽  
Minimum Duration ◽  
Additional Filter ◽  
Blocking Index

The Tibaldi-Molteni blocking index is supplemented by additional filter criteria to eliminate cut-off lows and subsynoptic structures. We introduce three blocking filters and analyse their sensitivities: (i) a quantile filter requiring a minimum geopotential height anomaly to reject cut-off lows, (ii) an extent filter to extract scales above a minimum zonal width, and (iii) a persistence filter to extract events with a minimum duration. Practical filter application is analysed in two case studies and the blocking climatologies for the Northern and the Southern Hemisphere.

The Role of Extratropical Air–Sea Interaction in the Autumn Subseasonal Variability of the North Atlantic Oscillation

2019 ◽  
Vol 32 (22) ◽  
pp. 7697-7712 ◽  
Author(s):  
Yu Nie ◽  
Hong-Li Ren ◽  
Yang Zhang
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Gulf Stream ◽  
Low Frequency ◽  
Mean Flow ◽  
The North ◽  
Subseasonal Variability ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Considerable progress has been made in understanding the internal eddy–mean flow feedback in the subseasonal variability of the North Atlantic Oscillation (NAO) during winter. Using daily atmospheric and oceanic reanalysis data, this study highlights the role of extratropical air–sea interaction in the NAO variability during autumn when the daily sea surface temperature (SST) variability is more active and eddy–mean flow interactions are still relevant. Our analysis shows that a horseshoe-like SST tripolar pattern in the North Atlantic Ocean, marked by a cold anomaly in the Gulf Stream and two warm anomalies to the south of the Gulf Stream and off the western coast of northern Europe, can induce a quasi-barotropic NAO-like atmospheric response through eddy-mediated processes. An initial southwest–northeast tripolar geopotential anomaly in the North Atlantic forces this horseshoe-like SST anomaly tripole. Then the SST anomalies, through surface heat flux exchange, alter the spatial patterns of the lower-tropospheric temperature and thus baroclinicity anomalies, which are manifested as the midlatitude baroclinicity shifted poleward and reduced baroclinicity poleward of 70°N. In response to such changes of the lower-level baroclinicity, anomalous synoptic eddy generation, eddy kinetic energy, and eddy momentum forcing in the midlatitudes all shift poleward. Meanwhile, the 10–30-day low-frequency anticyclonic wave activities in the high latitudes decrease significantly. We illustrate that both the latitudinal displacement of midlatitude synoptic eddy activities and intensity variation of high-latitude low-frequency wave activities contribute to inducing the NAO-like anomalies.

A revision of the New World genus Fidia Baly 1863 (Coleoptera: Chrysomelidae: Eumolpinae: Adoxini)

Zootaxa ◽  
2008 ◽  
Vol 1798 (1) ◽  
pp. 1 ◽  
Author(s):  
M. S. STROTHER ◽  
C. L. STAINES
Keyword(s):  
United States ◽  
Costa Rica ◽  
New World ◽  
Southeastern United States ◽  
Central American ◽  
Nomen Nudum ◽  
Distribution Maps ◽  
The North

The North and Central American genus Fidia Baly 1863 (Coleoptera: Chrysomelidae) is revised. The genus is redescribed and a diagnosis separating Fidia from similar genera is provided. Twenty-four species are recognized: F. lateralis Jacoby 1882 is transferred to Xanthonia; Colaspis flavescens Sturm 1826 is a nomen nudum; F. sallei Lefèvre 1877 and F. unistriata Jacoby 1882 are synonymized with F. albovittata Lefèvre 1877; F. atra Jacoby 1882 is synonymized with F. spuria Lefèvre 1877. Twelve species are described as new- F. chapini from Mexico; F. comalensis from Mexico; F. convexicollis from Texas and Oklahoma; F. costaricensis from Costa Rica; F. delilahae from Alabama and Mississippi; F. dicelloposthe from Mexico; F. dichroma from Mexico; F. marraverpa from Mexico; F. papillata from Mexico; F. pedinops from Alabama, Florida, and Georgia; F. rileyorum from the southeastern United States; and F. xanthonioides from Mexico. Lectotypes are designated for F. albovittata Lefèvre 1877, F. cana Horn 1892, F. guatemalensis Jacoby 1879, F. lurida Lefèvre 1885, F. plagiata Lefèvre 1877, F. sallei Lefèvre 1877, F. spuria Lefèvre 1877, and F. unistriata Jacoby 1882. A key to the recognized species is presented and important taxonomic characters are illustrated. Distribution maps are provided for each species.

scholarly journals Identification of the Eurasian–North Pacific Multidecadal Oscillation and Its Relationship to the AMO

2013 ◽  
Vol 26 (20) ◽  
pp. 8139-8153 ◽  
Author(s):  
Ming-Ying Lee ◽  
Huang-Hsiung Hsu
Keyword(s):  
North Pacific ◽  
Geopotential Height ◽  
Western Europe ◽  
Atlantic Multidecadal Oscillation ◽  
Warming Trend ◽  
Multidecadal Variability ◽  
Upper Troposphere ◽  
The North ◽  
The Tropics ◽  
The North Pacific

Abstract A multidecadal geopotential height pattern in the upper troposphere of the extratropical Northern Hemisphere (NH) is identified in this study. This pattern is characterized by the nearly zonal symmetry of geopotential height and temperature between 35° and 65°N and the equivalent barotropic vertical structure with the largest amplitude in the upper troposphere. This pattern is named the Eurasian–Pacific multidecadal oscillation (EAPMO) to describe its multidecadal time scale and the largest amplitudes over Eurasia and the North Pacific. Although nearly extending over the entire extratropics, the EAPMO exhibits larger amplitudes over western Europe, East Asia, and the North Pacific with a zonal scale equivalent to zonal wavenumbers 4 and 5. The zonally asymmetric perturbation tends to amplify over the major mountain ranges in the region, suggesting a significant topographic influence. The EAPMO has fluctuated concurrently with the Atlantic multidecadal oscillation (AMO) at least since the beginning of the twentieth century. The numerical simulation results suggest that the EAPMO could be induced by the AMO-like sea surface temperature anomaly and strengthened regionally by topography, especially over the Asian highland region, although the amplitude was undersimulated. This study found that the multidecadal variability of the upper-tropospheric geopotential height in the extratropical NH is much more complicated than in the tropics and the Southern Hemisphere (SH). It takes both first (warming trend) and second (multidecadal) EOFs to explain the multidecadal variability in the extratropical NH, while only the first EOF, which exhibited a warming trend, is sufficient for the tropics and SH.

Anomalous Temperature Regimes during the Cool Season: Long-Term Trends, Low-Frequency Mode Modulation, and Representation in CMIP5 Simulations

2013 ◽  
Vol 26 (22) ◽  
pp. 9061-9076 ◽  
Author(s):  
Rebecca M. Westby ◽  
Yun-Young Lee ◽  
Robert X. Black
Keyword(s):  
United States ◽  
Linear Regression Analysis ◽  
Low Frequency ◽  
The United States ◽  
Cmip5 Models ◽  
Southern United States ◽  
Anomalous Temperature ◽  
Temperature Regimes ◽  
Collective Influence

Abstract During boreal winter, anomalous temperature regimes (ATRs), including cold air outbreaks (CAOs) and warm waves (WWs), provide important societal influences upon the United States. The current study analyzes reanalysis and model data for the period from 1949 to 2011 to assess (i) long-term variability in ATRs, (ii) interannual modulation of ATRs by low-frequency modes, and (iii) the representation of ATR behavior in models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). No significant trends in either WWs or CAOs are identified for the continental United States. On interannual time scales, CAOs are modulated by the (i) North Atlantic Oscillation (NAO) over the U.S. Southeast and (ii) the Pacific–North American (PNA) pattern over the Northwest. WW frequency is modulated by (i) the NAO over the eastern United States and (ii) the combined influence of the PNA, Pacific decadal oscillation (PDO), and ENSO over the southern United States. In contrast to previous studies of seasonal-mean temperature, the influence of ENSO upon ATRs is found to be mainly limited to a modest modulation of WWs over the southern United States. Multiple linear regression analysis reveals that the regional collective influence of low-frequency modes accounts for as much as 50% of interannual ATR variability. Although similar behavior is observed in CMIP5 models, WW (CAO) frequency is typically overestimated (underestimated). All models considered are unable to replicate observed associations between ATRs and the PDO. Further, the collective influence of low-frequency modes upon ATRs is generally underestimated in CMIP5 models. The results indicate that predictions of future ATR behavior are limited by climate model ability to represent the evolving behavior of low-frequency modes of variability.

scholarly journals Regional Changes in the Interannual Variability of U.S. Warm Season Precipitation

2016 ◽  
Vol 29 (14) ◽  
pp. 5157-5173 ◽  
Author(s):  
Scott J. Weaver ◽  
Stephen Baxter ◽  
Kirstin Harnos
Keyword(s):  
United States ◽  
The United States ◽  
Precipitation Variability ◽  
Height Anomaly ◽  
Epochal Change ◽  
Upper Level ◽  
Recent Epoch ◽  
Level Height ◽  
Circulation Changes

Abstract Intensification of regional springtime precipitation variability over the United States and the role of North American low-level jets (NALLJs) are investigated for the 1950–2010 period. The analysis reveals that the primary modes of NALLJ fluctuations are related to the strengthening of AMJ precipitation variability over the northern Great Plains and southeastern United States during the last 60 years. Examination of the epochal change in NALLJ variations shows a stronger connectivity to SST variability during 1980–2010 than in the 1950–79 period. In the context of the first three NALLJ variability modes it appears that the role of decadal SST variations (NALLJ mode 1) and the recent emergence of tropical Pacific connectivity (NALLJ modes 1 and 2) via SST-induced atmospheric heating and large-scale circulation changes may act to strengthen and spatially shift the NALLJ variability modes southward and/or eastward, intensifying regional precipitation variability in the recent epoch. Although notable NALLJ variability also exists in the earlier epoch, the upper-level height field is significantly lacking in meridional gradients, leading to weak upper-level zonal wind anomalies over the United States and diminished NALLJ variability. Conversely, the intensified and spatially shifted upper-level height anomaly in the recent epoch produces enhanced meridional height gradients in all three modes, strengthening NALLJ variability—highlighting that seemingly subtle shifts in hemispheric-scale atmospheric circulation changes can have important impacts on regional climate variability and change.

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