Observational Studies of General Circulation Patterns

1951 ◽  
pp. 551-567 ◽  
Author(s):  
Jerome Namias ◽  
Philip F. Clapp
Keyword(s):  
Observational Studies ◽  
General Circulation ◽  
Circulation Patterns

scholarly journals Impact of COVID-19 Lockdown and Atmospheric Circulation on the Air Quality in Wuhan During Early 2020

2021 ◽  
Vol 299 ◽  
pp. 02011
Author(s):  
Youyong Xie ◽  
Xiefei Zhi
Keyword(s):  
Air Quality ◽  
Atmospheric Circulation ◽  
Air Pollutants ◽  
General Circulation ◽  
Circulation Pattern ◽  
Atmospheric Circulation Patterns ◽  
Atmospheric General Circulation ◽  
Circulation Patterns ◽  
The Impact

Previous studies indicated that the air quality was improved in Wuhan during COVID-19 lockdown. However, the impact of atmospheric general circulation on the changes of air quality has not been taken into account. The present study aims to discuss the improvement of air quality in Wuhan and its possible reasons during COVID-19 lockdown. The results showed that all air pollutants except O3 decreased in Wuhan during early 2020. The occurrence days of A, C, W and NW types’ circulation pattern during early 2020 are more than those during the same period of 1979-2020. The occurrence days of SW type’s circulation pattern is slightly less than those during early 1979-2020. With more occurrence days of these dominant atmospheric circulation patterns, the number of polluted days could rise in Wuhan during early 2020. Nevertheless, this scenario didn’t occur. The COVID-19 lockdown did improve the air quality in Wuhan during early 2020.

scholarly journals The dynamics of İzmir Bay under the effects of wind and thermohaline forces

Ocean Science ◽  
2018 ◽  
Vol 14 (2) ◽  
pp. 285-292
Author(s):  
Erdem Sayın ◽  
Canan Eronat
Keyword(s):  
Driving Force ◽  
General Circulation ◽  
Circulation Model ◽  
Aegean Sea ◽  
Circulation Pattern ◽  
Izmir Bay ◽  
Circulation Patterns ◽  
Westerly Winds ◽  
Seasonal Stratification ◽  
Sea Coast

Abstract. The dominant circulation pattern of İzmir Bay on the Aegean Sea coast of Turkey is studied taking into consideration the influence of wind and thermohaline forces. İzmir Bay is discussed by subdividing the bay into outer, middle and inner areas. Wind is the most important driving force in the İzmir coastal area. There are also thermohaline forces due to the existence of water types of different physical properties in the bay. In contrast to the two-layer stratification during summer, a homogeneous water column exists in winter. The free surface version of the Princeton model (Killworth's 3-D general circulation model) is applied, with the input data obtained through the measurements made by the research vessel K. Piri Reis. As a result of the simulations with artificial wind, the strong consistent wind generates circulation patterns independent of the seasonal stratification in the bay. Wind-driven circulation causes cyclonic or anticyclonic movements in the middle bay where the distinct İzmir Bay Water (IBW) forms. Cyclonic movement takes place under the influence of southerly and westerly winds. On the other hand, northerly and easterly winds cause an anticyclonic movement in the middle bay. The outer and inner bay also have the wind-driven recirculation patterns expected.

scholarly journals Climate change and outbreaks of amphibian chytridiomycosis in a montane area of Central Spain; is there a link?

2006 ◽  
Vol 274 (1607) ◽  
pp. 253-260 ◽  
Author(s):  
Jaime Bosch ◽  
Luís M Carrascal ◽  
Luis Durán ◽  
Susan Walker ◽  
Matthew C Fisher
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
Batrachochytrium Dendrobatidis ◽  
Global Scale ◽  
Amphibian Species ◽  
The North ◽  
Natural Park ◽  
Circulation Patterns ◽  
The North Atlantic Oscillation

Amphibian species are declining at an alarming rate on a global scale in large part owing to an infectious disease caused by the chytridiomycete fungus, Batrachochytrium dendrobatidis . This disease of amphibians has recently emerged within Europe, but knowledge of its effects on amphibian assemblages remains poor. Importantly, little is known about the environmental envelope that is associated with chytridiomycosis in Europe and the potential for climate change to drive future disease dynamics. Here, we use long-term observations on amphibian population dynamics in the Peñalara Natural Park, Spain, to investigate the link between climate change and chytridiomycosis. Our analysis shows a significant association between change in local climatic variables and the occurrence of chytridiomycosis within this region. Specifically, we show that rising temperature is linked to the occurrence of chytrid-related disease, consistent with the chytrid-thermal-optimum hypothesis. We show that these local variables are driven by general circulation patterns, principally the North Atlantic Oscillation. Given that B. dendrobatidis is known to be broadly distributed across Europe, there is now an urgent need to assess the generality of our finding and determine whether climate-driven epidemics may be expected to impact on amphibian species across the wider region.

Spatial early warnings of the transition to superrotation: Studying a bifurcation in the general circulation using an idealized GCM

2020 ◽  
Author(s):  
mark williamson
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Global Circulation ◽  
The Earth ◽  
Current Thinking ◽  
Circulation Patterns ◽  
Spatial Modes ◽  
Risk Event ◽  
Low Probability

<p>A superrotating atmosphere, one in which the angular momentum of the atmosphere exceeds the solid body rotation of the planet, occurs on Venus and Titan. However, it may have occurred on the Earth in the hot house climates of the Early Cenozoic and some climate models have transitioned abruptly to a superrotating state under the more extreme global warming scenarios. Applied to the Earth, the transition to superrotation causes the prevailing easterlies at the equator to become westerlies and accompanying large changes in global circulation patterns. Although current thinking is that this scenario is unlikely, it shares features of other global tipping points in that it is a low probability, high risk event.</p><p>More than anything though, this tipping point serves as an ideal example to test some spatial early warning methods. I’ll show some preliminary results how the critical spatial modes and time scales change through the transition to superrotation using an idealized general circulation model (GCM), Isca.</p>

scholarly journals On the outflow of dense water from the Weddell and Ross Seas in OCCAM model

Ocean Science ◽  
2012 ◽  
Vol 8 (3) ◽  
pp. 369-388 ◽  
Author(s):  
R. Kerr ◽  
K. J. Heywood ◽  
M. M. Mata ◽  
C. A. E. Garcia
Keyword(s):  
Observational Studies ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Weddell Sea ◽  
Global Ocean ◽  
Antarctic Bottom Water ◽  
Dense Water ◽  
Cumulative Volume ◽  
Volume Transports

Abstract. We describe the seasonal and interannual variability of volume transports in the Weddell and Ross Seas using the 1/12° 20-yr simulation of the OCCAM global ocean general circulation model. The average simulated full-depth cumulative volume transports were 28.5 ± 2.9 Sv (1 Sv ≡ 106 m3 s−1) and 13.4 ± 5.2 Sv, across the main export regions of the Weddell and Ross Seas, respectively. The values of mean outflow of Antarctic Bottom Water (AABW) (defined by neutral density γn ≥ 28.27 kg m−3) from the Weddell and Ross Seas of 10.6 ± 3.1 Sv and 0.5 ± 0.7 Sv, respectively, agree with the range reported in historical observational studies. The export of Weddell Sea dense water in OCCAM is primarily determined by the strength of the Weddell Gyre. Variability in AABW export is predominantly at periods of ~1 yr and 2–4 yr.

scholarly journals Quantifying Differences in Circulation Patterns Based on Probabilistic Models: IPCC AR4 Multimodel Comparison for the North Atlantic*

2010 ◽  
Vol 23 (24) ◽  
pp. 6573-6589 ◽  
Author(s):  
Henning W. Rust ◽  
Mathieu Vrac ◽  
Matthieu Lengaigne ◽  
Benjamin Sultan
Keyword(s):  
Climate Change ◽  
North Atlantic ◽  
General Circulation ◽  
Gaussian Mixture ◽  
Reanalysis Data ◽  
Shape Information ◽  
Size And Shape ◽  
The North ◽  
Circulation Patterns ◽  
The North Atlantic

Abstract The comparison of circulation patterns (CPs) obtained from reanalysis data to those from general circulation model (GCM) simulations is a frequent task for model validation, downscaling of GCM simulations, or other climate change–related studies. Here, the authors suggest a set of measures to quantify the differences between CPs. A combination of clustering using Gaussian mixture models with a set of related difference measures allows for taking cluster size and shape information into account and thus provides more information than the Euclidean distances between cluster centroids. The characteristics of the various distance measures are illustrated with a simple simulated example. Subsequently, a five-component Gaussian mixture to define circulation patterns for the North Atlantic region from reanalysis data and GCM simulations is used. CPs are obtained independently for the NCEP–NCAR reanalysis and the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), as well as for twentieth-century simulations from 14 GCMs of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) database. After discussing the difference of CPs based on spherical and nonspherical clusters for the reanalysis datasets, the authors give a detailed evaluation of the cluster configuration for two GCMs relative to NCEP–NCAR. Finally, as an illustration, the capability of reproducing the NCEP–NCAR probability density function (pdf) defining the Greenland anticyclone CP is evaluated for all 14 GCMs, considering that the size and shape of the underlying pdfs complement the commonly used Euclidean distance of CPs’ mean values.

scholarly journals Influence of Dardanelles outflow induced thermal fronts and winds on drifter trajectories in the Aegean Sea

2014 ◽  
Vol 15 (2) ◽  
pp. 239 ◽  
Author(s):  
R. GERIN ◽  
V. KOURAFALOU ◽  
P.-M. POULAIN ◽  
Ş. BESIKTEPE
Keyword(s):  
Black Sea ◽  
General Circulation ◽  
Aegean Sea ◽  
The Black Sea ◽  
Data Set ◽  
Strong Connectivity ◽  
Surface Circulation ◽  
Circulation Patterns ◽  
Modelling Studies

The data provided by 12 drifters deployed in the Northern Aegean Sea in the vicinity of the Dardanelles Strait in August 2008 and February 2009 are used to explore the surface circulation of the basin and the connectivity to the Black Sea. The drifters were deployed within the Dardanelles outflow of waters of Black Sea origin in the Northeastern Aegean. Thanks to the particular choice of the drifter deployment positions, the data set provides a unique opportunity to observe the branching behaviour of the surface currents around Lemnos Island. Such pathways were notpossible to study with previous drifter deployments that were far from the Dardanelles Strait. In addition, the drifter tracks covered the Aegean basin quite thoroughly, mapping major circulation features and supporting the overall general circulation patterns described by previous observational and modelling studies. The collected data display cases in which drifters are driven by winds and thermal fronts. Wind products were used to estimate the influence of the atmospheric forcing on the drifter trajectories. Satellite sea surface temperature images were connected to the drifter tracks, demonstrating a high correlation between the remote and in situ observations. The waters of Black Sea origin were traced all the way to the Southern Aegean, establishing a strong connectivity link between the Aegean and Black Sea basins.

Quantifying late Quaternary Australian rainfall seasonality changes using the Poaceae:Asteraceae pollen ratio

2020 ◽  
pp. 1-15
Author(s):  
Annika V. Herbert ◽  
Jennifer M. Fitchett
Keyword(s):  
South Africa ◽  
General Circulation ◽  
Late Quaternary ◽  
Climatic Changes ◽  
Double Peak ◽  
Circulation Patterns ◽  
Rainfall Seasonality ◽  
Westerly Winds ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract Mounting evidence suggests that the Southern Westerly Winds were significantly equatorially displaced and more intense during the last glacial maximum (LGM), prompting deliberate research identifying proxies to reconstruct these changes. This has focused on rainfall seasonality to track changes in major circulation patterns across the southern hemisphere midlatitude regions. Using a common methodology to reconstruct climatic changes aids comparability and makes it easier to draw significant conclusions regarding general circulation movements. We assess the applicability of Coetzee's (1967) Poaceae:Asteraceae pollen ratio, which has been used successfully in South Africa, in the Australian context. The ratio scores from modern samples fail to capture the weak seasonality in the southeast and on Tasmania but is successful for the rest of the continent. The periods of greatest change compared to present day match known periods of distinct climatic events, namely the mid-Holocene (6–7 cal ka BP), the last deglacial period (15–17 cal ka BP), and two periods during the LGM (20–22 and 31–33 cal ka BP), suggesting large parts of Australia experienced a “double peak” of rainfall seasonality change during the LGM. This confirms that the Poaceae:Asteraceae pollen ratio can be used on records outside of South Africa.

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