scholarly journals Un indice climatique contrôlant les conditions de vagues en hiver le long de la côte atlantique européenne : WEPA (West Europe Pressure Anomaly)

2018 ◽  
Author(s):  
Bruno CASTELLE ◽  
Guillaume DODET ◽  
Gerd MASSELINK ◽  
Tim SCOTT
Keyword(s):  
Pressure Anomaly

scholarly journals Subseasonal relationship between Arctic and Eurasian surface air temperature

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hye-Jin Kim ◽  
Seok-Woo Son ◽  
Woosok Moon ◽  
Jong-Seong Kug ◽  
Jaeyoung Hwang
Keyword(s):  
Air Temperature ◽  
Diabatic Heating ◽  
Surface Air Temperature ◽  
Significant Negative Correlation ◽  
Cold Season ◽  
Reanalysis Data ◽  
Necessary Condition ◽  
Sea Level Pressure ◽  
Blocking High ◽  
Pressure Anomaly

AbstractThe subseasonal relationship between Arctic and Eurasian surface air temperature (SAT) is re-examined using reanalysis data. Consistent with previous studies, a significant negative correlation is observed in cold season from November to February, but with a local minimum in late December. This relationship is dominated not only by the warm Arctic-cold Eurasia (WACE) pattern, which becomes more frequent during the last two decades, but also by the cold Arctic-warm Eurasia (CAWE) pattern. The budget analyses reveal that both WACE and CAWE patterns are primarily driven by the temperature advection associated with sea level pressure anomaly over the Ural region, partly cancelled by the diabatic heating. It is further found that, although the anticyclonic anomaly of WACE pattern mostly represents the Ural blocking, about 20% of WACE cases are associated with non-blocking high pressure systems. This result indicates that the Ural blocking is not a necessary condition for the WACE pattern, highlighting the importance of transient weather systems in the subseasonal Arctic-Eurasian SAT co-variability.

scholarly journals A “Cold Path” for the Gulf Stream–Troposphere Connection

2017 ◽  
Vol 30 (4) ◽  
pp. 1363-1379 ◽  
Author(s):  
Benoît Vannière ◽  
Arnaud Czaja ◽  
Helen Dacre ◽  
Tim Woollings
Keyword(s):  
Boundary Layer ◽  
Gulf Stream ◽  
Surface Wind ◽  
Extratropical Cyclone ◽  
Convective Precipitation ◽  
Dynamical Response ◽  
Sst Front ◽  
Simple Boundary ◽  
Pressure Anomaly ◽  
Sst Gradient

Abstract The mechanism by which the Gulf Stream sea surface temperature (SST) front anchors a band of precipitation on its warm edge is still a matter of debate, and little is known about how synoptic activity contributes to the mean state. In the present study, the influence of the SST front on precipitation is investigated during the course of a single extratropical cyclone using a regional configuration of the Met Office Unified Model. The comparison of a control run with a simulation in which SST gradients were smoothed brought the following conclusions: a band of precipitation is reproduced for a single extratropical cyclone, and the response to the SST gradient is dominated by a change of convective precipitation in the cold sector of the storm. Several climatological features described by previous studies, such as surface wind convergence on the warm edge or a meridional circulation cell across the SST front, are also reproduced at synoptic time scales in the cold sector. Based on these results, a simple boundary layer model is proposed to explain the convective and dynamical response to the SST gradient in the cold sector. In this model, cold and dry air parcels acquire more buoyancy over a sharp SST gradient and become more convectively unstable. The convection sets a pressure anomaly over the entire depth of the boundary layer that drives wind convergence. This case study offers a new pathway by which the SST gradient can anchor a climatological band of precipitation.

scholarly journals Dynamical Processes Related to the Appearance of the Okhotsk High during Early Midsummer

2007 ◽  
Vol 20 (19) ◽  
pp. 4982-4994 ◽  
Author(s):  
Naoki Sato ◽  
Masaaki Takahashi
Keyword(s):  
Energy Conversion ◽  
Heat Budget ◽  
Lower Troposphere ◽  
Positive Pressure ◽  
Basic Field ◽  
Anomaly Field ◽  
Anomaly Pattern ◽  
Pressure Anomaly ◽  
Okhotsk High ◽  
Upper Level

Abstract The authors identified an upper-level pressure anomaly pattern corresponding to the interannual variability of the Okhotsk high in midsummer (late July and early August) as a predominant anomaly pattern in the Northern Hemisphere, by using objectively analyzed data. According to the results of empirical orthogonal function (EOF) analyses and composite analyses, a positive pressure anomaly appeared near the tropopause over eastern Siberia in years with strong Okhotsk highs. Examination of the heat budget in the lower troposphere revealed that a negative surface temperature anomaly observed in northern Japan was brought by the advection of the climatological temperature gradient from the anomalous wind associated with the upper-level anticyclonic anomaly. It was also demonstrated that the anomaly field over Siberia does not accompany predominant vorticity forcing or Rossby wave propagation from the west with a specific phase. However, positive kinetic energy conversion from the climatological basic field to the anomaly field is estimated. The energy conversion contributes to maintaining the anomaly pattern. By the numerical experiments using a linear barotropic model, it is suggested that the upper-level anomaly pattern related to the anomalous Okhotsk high appears through the interaction with the climatological basic field, even though the external forcings are homogeneously distributed.

scholarly journals The Icelandic Low as a Predictor of the Gulf Stream North Wall Position

2016 ◽  
Vol 46 (3) ◽  
pp. 817-826 ◽  
Author(s):  
Alejandra Sanchez-Franks ◽  
Sultan Hameed ◽  
Robert E. Wilson
Keyword(s):  
Gulf Stream ◽  
Southern Oscillation ◽  
Time Lags ◽  
Grand Banks ◽  
The North ◽  
Cape Hatteras ◽  
Pressure Anomaly ◽  
Icelandic Low ◽  
North Wall ◽  
Wall Position

AbstractThe Gulf Stream’s north wall east of Cape Hatteras marks the abrupt change in velocity and water properties between the slope sea to the north and the Gulf Stream itself. An index of the north wall position constructed by Taylor and Stephens, called Gulf Stream north wall (GSNW), is analyzed in terms of interannual changes in the Icelandic low (IL) pressure anomaly and longitudinal displacement. Sea surface temperature (SST) composites suggest that when IL pressure is anomalously low, there are lower temperatures in the Labrador Sea and south of the Grand Banks. Two years later, warm SST anomalies are seen over the Northern Recirculation Gyre and a northward shift in the GSNW occurs. Similar changes in SSTs occur during winters in which the IL is anomalously west, resulting in a northward displacement of the GSNW 3 years later. Although time lags of 2 and 3 years between the IL and the GSNW are used in the calculations, it is shown that lags with respect to each atmospheric variable are statistically significant at the 5% level over a range of years. Utilizing the appropriate time lags between the GSNW index and the IL pressure and longitude, as well as the Southern Oscillation index, a regression prediction scheme is developed for forecasting the GSNW with a lead time of 1 year. This scheme, which uses only prior information, was used to forecast the GSNW from 1994 to 2015. The correlation between the observed and forecasted values for 1994–2014 was 0.60, significant at the 1% level. The predicted value for 2015 indicates a small northward shift of the GSNW from its 2014 position.

Atmospheric response to Gulf Stream SST front shifting: impact of horizontal resolution in an ensemble of global climate models

2021 ◽  
Author(s):  
Luca Famooss Paolini ◽  
Alessio Bellucci ◽  
Paolo Ruggieri ◽  
Panos Athanasiadis ◽  
Silvio Gualdi
Keyword(s):  
High Resolution ◽  
Gulf Stream ◽  
General Circulation ◽  
Diabatic Heating ◽  
Storm Track ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Atmospheric Response ◽  
Sst Front ◽  
Pressure Anomaly

<p>Western boundary currents transport a large amount of heat from the Tropics toward higher latitudes; furthermore they are characterized by a strong sea surface temperature (SST) gradient, which anchors zones of intense upward motion extending up to the upper-troposphere and shapes zones of intense baroclinic eddy activity (storm tracks). For such reasons they have been shown to be fundamental in influencing the climate of the Northern Hemisphere and its variability, and a potentially relevant source of atmospheric predictability. </p><p> </p><p>General circulation models show deficiencies in simulating the observed atmospheric response to SST front variability. The atmospheric horizontal resolution has been recently proposed as a key element in understanding such differences. However, the number of studies on this subject is still limited. Furthermore, a multi-model analysis to systematically investigate differences between low-resolution and high-resolution atmospheric response to oceanic forcing is still lacking. </p><p> </p><p>The present work has the objective to fill this gap, analysing the atmospheric response to Gulf Stream SST front shifting using data from recent High Resolution Model Intercomparison Project (HighResMIP). This project was designed with the specific objective of investigating the impact of increased model horizontal resolution on the representation of the observed climate. Ensembles of historical simulations performed with three atmospheric general circulation models (AGCMs) have been analysed, each conducted with a low-resolution (LR, about 1°) and a high-resolution (HR, about 0.25°) configuration. AGCMs have been forced with observed SSTs (HadISST2 dataset), available at daily frequency on a 0.25° grid, during 1950–2014. </p><p><br>Results show atmospheric responses to the SST-induced diabatic heating anomalies that are strongly resolution dependent. In LR simulations a low-pressure anomaly is present downstream of the SST anomaly, while the diabatic heating anomaly is mainly balanced by meridional advection of air coming from higher latitudes, as expected for an extra-tropical shallow heat source. In contrast, HR simulations generate a high-pressure anomaly downstream of the SST anomaly, thus driving positive temperature advection from lower latitudes (not balancing diabatic heating). Along the vertical direction, both in LR and HR simulation, the diabatic heating in the interior of the atmosphere is balanced by upward motion south of GS SST front and downward motion north and further south of the Gulf Stream. Finally, LR simulations show a reduction in storm-track activity over the North Atlantic, whereas HR simulations show a meridional displacement of the storm-track considerably larger (yet in the same direction) than that of the SST front. HR simulations reproduce the atmospheric response obtained from observations, albeit weaker. This is a hint for the existence of a positive feedback between ocean and atmosphere, as proposed in previous studies. These findings are qualitatively consistent with previous results in literature and, leveraging on recent coordinated modelling efforts, shed light on the effective role of atmospheric horizontal resolution in modelling the atmospheric response to extra-tropical oceanic forcing.</p>

scholarly journals Regionally-Coherent Embayment Rotation: Behavioural Response to Bi-Directional Waves and Atmospheric Forcing

2019 ◽  
Vol 7 (4) ◽  
pp. 116 ◽  
Author(s):  
Mark Wiggins ◽  
Tim Scott ◽  
Gerd Masselink ◽  
Paul Russell ◽  
Nieves G. Valiente
Keyword(s):  
Wave Power ◽  
Rotational Behaviour ◽  
Easterly Waves ◽  
Wave Forcing ◽  
The North ◽  
Directional Waves ◽  
Pressure Anomaly ◽  
Forcing Mechanisms ◽  
Beach Rotation ◽  
The North Atlantic Oscillation

Bi-directional wave climates often drive beach rotation, increasing erosional risk at semi-sheltered locations. Identification of rotation and forcing mechanisms is vital to future coastal defence. In this study, regional investigation of modelled wave data revealed strong bi-directionality between dominant south-westerly and sub-dominant easterly waves for 14 offshore locations along the length of the south coast of England, U.K. South-westerly wave power was well correlated to positive phases of the West Europe Pressure Anomaly (WEPA), whilst easterly wave power was well correlated with negative phases of the North Atlantic Oscillation (NAO). Additionally, decadal records of beach morphological change and associated wave forcing, were investigated for 22 coastal sites across the same region. Significant rotational behaviour was identified at 11 sites, leading to the creation of a rotation index. Beach rotation was attributed to shoreline angle, with the strongest rotation occurring at south-east-facing beaches, with high obliquity to dominant south-westerly waves. The beach rotation index was well correlated with the normalized balance of wave power from opposing south-westerly and easterly directions. Direct correlations between beach rotation and WEPA at two sites showed that future forecasts of atmospheric indices may allow prediction of rotational beach state, at seasonal scales.

Winter climate change on the northern and southern Antarctic Peninsula

2020 ◽  
Vol 32 (5) ◽  
pp. 408-424
Author(s):  
Oleksandr M. Evtushevsky ◽  
Volodymyr O. Kravchenko ◽  
Asen V. Grytsai ◽  
Gennadi P. Milinevsky
Keyword(s):  
Time Series ◽  
Surface Temperature ◽  
Antarctic Peninsula ◽  
Southern Annular Mode ◽  
Meridional Wind ◽  
Winter Climate ◽  
Annular Mode ◽  
Temperature Trends ◽  
Pressure Anomaly ◽  
Tropical Sea

AbstractDifferences in the decadal trend in the winter surface temperature in the northern and southern Antarctic Peninsula have been analysed. Time series from the two stations Esperanza and Faraday/Vernadsky since the early 1950s are used. The two time series are strongly correlated only during the 1980s and 1990s when their variability and trends are associated with both the Niño-4 region and Southern Annular Mode impacts. The winter cooling at the Faraday/Vernadsky station contrasts with the winter warming at the Esperanza station during the period of 2006–17. The different temperature trends are accompanied by weak correlations between the temperatures at these two stations. Linearly congruent components of the station temperature trends in 2006–17 indicate a dominant contribution of Southern Annular Mode (tropical sea surface temperature anomalies) to warming (cooling) in the northern (southern) Peninsula. Distinctive impacts of climate modes are observed in combination with the recent deepening of the negative sea-level pressure anomaly to the west of the peninsula and the related change in the zonal and meridional wind components. These factors apparently contribute to the occurrence of the boundary that crosses the peninsula and divides it into sub-regions with warming and cooling.

High-pressure anomaly in the normal state ofMgB2

2004 ◽  
Vol 70 (18) ◽  
Author(s):  
P. Modak ◽  
A. K. Verma ◽  
D. M. Gaitonde ◽  
R. S. Rao ◽  
B. K. Godwal
Keyword(s):  
High Pressure ◽  
Normal State ◽  
Pressure Anomaly

Variations in Precipitation across the Southern Ocean

2020 ◽  
Vol 33 (24) ◽  
pp. 10653-10670
Author(s):  
M. J. Manton ◽  
Y. Huang ◽  
S. T. Siems
Keyword(s):  
Southern Ocean ◽  
Climate Model ◽  
Southern Oscillation ◽  
Zonal Flow ◽  
Southern Annular Mode ◽  
Accurate Estimate ◽  
Precipitation Anomaly ◽  
Unique Region ◽  
Pressure Anomaly ◽  
Climate Model Simulations

AbstractThe Southern Ocean lies beneath a unique region of the global atmosphere with minimal effects of landmasses on the zonal flow. The absence of landmasses also means that in situ observations of precipitation are limited to a few ocean islands. Two reanalyses and two satellite-based gridded datasets are analyzed to estimate the character of the distribution of precipitation across the region. The latitudinal variation is computed across three longitudinal sectors, representing the Pacific, Atlantic, and Indian Oceans. The most recent ECMWF reanalysis (ERA5) is found to produce the most accurate estimate of the mean profile and seasonal cycle of precipitation. However, there is little consistency in the estimates of trends in monthly anomalies of precipitation. A more consistent description of precipitation trends is found by using linear regression of the precipitation anomaly with the local mean sea level pressure anomaly, the southern annular mode, and the Southern Oscillation index. In broad terms, precipitation is found to be decreasing at lower latitudes and increasing at higher latitudes, which is consistent with earlier climate model simulations on the impacts of anthropogenic climate change.

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