scholarly journals Decadal variability and trends of the Benguela Upwelling System as simulated in a high-resolution ocean simulation

2015 ◽  
Vol 12 (2) ◽  
pp. 403-447
Author(s):  
N. Tim ◽  
E. Zorita ◽  
B. Hünicke
Keyword(s):  
Statistical Analysis ◽  
Pressure Gradient ◽  
Sea Level ◽  
Wind Stress ◽  
Large Scale ◽  
Sea Level Pressure ◽  
Subtropical Anticyclone ◽  
Level Pressure ◽  
Benguela Upwelling ◽  
Atmospheric Variables

Abstract. Detecting the atmospheric drivers of the Benguela Upwelling Systems is essential to understand its present variability and its past and future changes. We present a statistical analysis of an ocean-only simulation driven by observed atmospheric fields over the last decades with the aim of identifying the large-scale atmospheric drivers of upwelling variability and trends. The simulation is found to reproduce well the seasonal cycle of upwelling intensity, with a maximum in the June-to-August season in North Benguela and in the December-to-February season in South Benguela. The statistical analysis of the interannual variability of upwelling focuses on its relationship to atmospheric variables (sea level pressure, 10 m-wind, wind stress). The relationship between upwelling and the atmospheric variables differ somewhat in the two regions, but generally, the correlation patterns reflect the common atmospheric pattern favoring upwelling: southerly wind/wind stress, strong subtropical anticyclone, and an ocean-land sea level pressure gradient. In addition, the statistical link between upwelling and large-scale climate variability modes was analyzed. The El Niño Southern Oscillation and the Antarctic Oscillation exert some influence on austral summer upwelling velocities in South Benguela. The decadal evolution and the long-term trends of upwelling and of ocean-minus-land air pressure gradient do not agree with Bakun's hypothesis that anthropogenic climate change should generally intensify coastal upwelling.

scholarly journals Decadal variability and trends of the Benguela upwelling system as simulated in a high-resolution ocean simulation

Ocean Science ◽  
2015 ◽  
Vol 11 (3) ◽  
pp. 483-502 ◽  
Author(s):  
N. Tim ◽  
E. Zorita ◽  
B. Hünicke
Keyword(s):  
Statistical Analysis ◽  
High Resolution ◽  
Pressure Gradient ◽  
Sea Level ◽  
Wind Stress ◽  
Large Scale ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Benguela Upwelling ◽  
Atmospheric Variables

Abstract. Detecting the atmospheric drivers of the Benguela upwelling systems is essential to understand its present variability and its past and future changes. We present a statistical analysis of a high-resolution (0.1°) ocean-only simulation driven by observed atmospheric fields over the last 60 years with the aim of identifying the large-scale atmospheric drivers of upwelling variability and trends. The simulation is found to reproduce well the seasonal cycle of upwelling intensity, with a maximum in the June–August season in North Benguela and in the December–February season in South Benguela. The statistical analysis of the interannual variability of upwelling focuses on its relationship to atmospheric variables (sea level pressure, 10 m wind, wind stress). The relationship between upwelling and the atmospheric variables differ somewhat in the two regions, but generally the correlation patterns reflect the common atmospheric pattern favouring upwelling: southerly wind/wind stress, strong subtropical anticyclone, and an ocean–land sea level pressure gradient. In addition, the statistical link between upwelling and large-scale climate variability modes was analysed. The El Niño–Southern Oscillation and the Antarctic Oscillation exert some influence on austral summer upwelling velocities in South Benguela. The decadal evolution and the long-term trends of simulated upwelling and of ocean-minus-land air pressure gradient do not agree with Bakun's hypothesis that anthropogenic climate change should generally intensify coastal upwelling.

scholarly journals Influence of Long-Term Changes in the Large-Scale Sea Level Pressure Field on the Wind Regime and the Wind Stress Curl in the Black Sea

2021 ◽  
Vol 28 (2) ◽  
Author(s):  
I. G. Shokurova ◽  
A. A. Kubryakov ◽  
M. V. Shokurov ◽  
◽  
◽  
...  
Keyword(s):  
Sea Level ◽  
Black Sea ◽  
Wind Stress ◽  
Large Scale ◽  
Pressure Field ◽  
The Black Sea ◽  
Wind Stress Curl ◽  
Sea Level Pressure ◽  
Level Pressure

Purpose. The paper is aimed at studying the relationship between the wind regime and the wind stress curl in the Black Sea and the long-term changes in the large-scale sea level pressure field in winter months. Methods and Results. The data on wind speed and sea level pressure in January – February from the NCEP/NСAR reanalysis for 1948–2018 are used. Based on the 6-hour data, the synoptic conditions accompanied by high and low values of the wind stress curl in the sea were determined. The synoptic situations in which a vast anticyclone is located north and northeast of the sea, and the area of low pressure – to the southwest of the sea in the Mediterranean region, are accompanied by the northeast and east winds, and by the cyclonic curl predominance. On the contrary, passing of the cyclones to the north of the sea and increase of pressure to the southwest are followed by the westerly and southwesterly winds, and by the anticyclonic curl predominance. Extremely high monthly mean values of the cyclonic curl were observed in those years, when the area occupied by the Siberian anticyclone increased and expanded westward, so that the Black Sea was on the southwestern periphery of its spur. Extremely low values of the anticyclonic curl were noted when the Azores anticyclone area expanded to the Mediterranean region. The wind stress curl changes on the multidecadal scales have shown its relation to the global changes in the field of the sea level pressure and the sign of the pressure anomalies at the low latitudes. Conclusions. The opposite sign of the surface pressure anomalies to the northeast and southwest of the sea is accompanied by the highest values of the wind stress curl.

scholarly journals European precipitation connections with large-scale mean sea-level pressure (MSLP) fields

2013 ◽  
Vol 58 (2) ◽  
pp. 310-327 ◽  
Author(s):  
David Lavers ◽  
Christel Prudhomme ◽  
David M. Hannah
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Sea Level Pressure ◽  
Mean Sea Level ◽  
Level Pressure

Searching for resemblance between large-scale sea level pressure patterns leading to “intense” precipitation events over Italy

2008 ◽  
Vol 95 (1-2) ◽  
pp. 183-196 ◽  
Author(s):  
N. Tartaglione ◽  
M. Maugeri ◽  
F. Dalan ◽  
M. Brunetti ◽  
T. Nanni ◽  
...  
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Intense Precipitation ◽  
Precipitation Events

Variability of Saharan Cyclone Tracks, I: Climatology Study

2021 ◽  
Author(s):  
Abdulhaleem H. Labban ◽  
Adel M. Awad
Keyword(s):  
Statistical Analysis ◽  
Sea Level ◽  
Nearest Neighbor ◽  
Sea Level Pressure ◽  
Study Region ◽  
Mean Sea Level ◽  
Level Pressure ◽  
Cyclone Tracks ◽  
Monthly Distribution ◽  
Area Of Influence

Abstract Objectively, Saharan cyclones have been detected for the period from 1967 to 2019 using mean sea level pressure (SLP); their tracks have been specified from nearest neighbor cyclonic positions and classified into long/short tracks depending on the area of influence of the cyclones. Additionally, the detected long tracks have been objectively classified into five main routes directed generally eastward, northeastward and northward, accounting for approximately 41.6%, 19.7% and 30.4% of the total long tracks, respectively. Mainly for long tracks, three cyclogenesis areas, where more than 99% of cyclones are generated, were identified, with more than 61% generated in the Atlas region. Moreover, four far cyclolysis areas were identified, where approximately 74% of these cyclones terminated, with more than 66% of them terminating in the eastern study region. Furthermore, statistical analysis indicated that Saharan cyclones are commonly generated in the spring and summer, with ~35.3% and 46.3%, respectively. However, the highest numbers occur in spring in the northern Saharan and in summer in the southern Saharan, with ~49.1% and 57.7%, respectively. Temporally, the monthly distribution indicates that most of the cyclones moving along the five main routes are generated in warm months, namely, May to August. Approximately 85% of these cyclones have a lifespan of three days, while only 1% span more than five days.

Graphical Determination of the Geostrophic Wind Over a Point or Small Area

1952 ◽  
Vol 33 (8) ◽  
pp. 326-328
Author(s):  
John E. Hovde ◽  
Carl M. Reber
Keyword(s):  
Pressure Gradient ◽  
Sea Level ◽  
Total Pressure ◽  
Small Area ◽  
Geostrophic Wind ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Sea Level Pressure ◽  
Level Pressure

Assuming straight, parallel, and equally-spaced contour heights or isobars over a small area, the total pressure-gradient force (and the geostrophic wind) may be determined graphically using the contour-height or sea-level pressure differences between 3 stations around the area. The method is objective and eliminates personal discrepancies in scaling geostrophic wind from pressure or contour-height analyses.

scholarly journals Patterns of Sea Ice Retreat in the Transition to a Seasonally Ice-Free Arctic

2016 ◽  
Vol 29 (19) ◽  
pp. 6993-7008 ◽  
Author(s):  
Patricia DeRepentigny ◽  
L. Bruno Tremblay ◽  
Robert Newton ◽  
Stephanie Pfirman
Keyword(s):  
Sea Ice ◽  
Sea Level ◽  
Large Scale ◽  
System Model ◽  
The Arctic ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
The Pacific ◽  
Ice Retreat ◽  
Sea Ice Retreat

Abstract The patterns of sea ice retreat in the Arctic Ocean are investigated using two global climate models (GCMs) that have profound differences in their large-scale mean winter atmospheric circulation and sea ice drift patterns. The Community Earth System Model Large Ensemble (CESM-LE) presents a mean sea level pressure pattern that is in general agreement with observations for the late twentieth century. The Community Climate System Model, version 4 (CCSM4), exhibits a low bias in its mean sea level pressure over the Arctic region with a deeper Icelandic low. A dynamical mechanism is presented in which large-scale mean winter atmospheric circulation has significant effect on the following September sea ice extent anomaly by influencing ice divergence in specific areas. A Lagrangian model is used to backtrack the 80°N line from the approximate time of the melt onset to its prior positions throughout the previous winter and quantify the divergence across the Pacific and Eurasian sectors of the Arctic. It is found that CCSM4 simulates more sea ice divergence in the Beaufort and Chukchi Seas and less divergence in the Eurasian seas when compared to CESM-LE, leading to a Pacific-centric sea ice retreat. On the other hand, CESM-LE shows a more symmetrical retreat between the Pacific, Eurasian, and Atlantic sectors of the Arctic. Given that a positive trend in the Arctic Oscillation (AO) index, associated with low sea level pressure anomalies in the Arctic, is a robust feature of GCMs participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5), these results suggest that the sea ice retreat in the Pacific sector could be amplified during the transition to a seasonal ice cover.

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