Development of longitudinal dunes under Pangaean atmospheric circulation

2021 ◽  
Author(s):  
Hiroki Shozaki ◽  
Hitoshi Hasegawa
Keyword(s):  
Atmospheric Circulation ◽  
Global Climate ◽  
Surface Wind ◽  
Hadley Circulation ◽  
Lower Jurassic ◽  
Wind Pattern ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Induced Changes ◽  
Wind Patterns

Abstract. As a result of the large difference in heat capacity between land and ocean, global climate and atmospheric circulation patterns in the supercontinent Pangaea were significantly different from today. Modelling experiments have suggested the seasonal overturning of cross-equatorial Hadley circulation; however, there are large discrepancies between model-generated surface wind patterns and the reported palaeo-wind directions from aeolian dune records. Here, we present the results of measurements of spatial distribution of dune slip-face azimuths recorded in Lower Jurassic aeolian sandstones over a wide area of the western United States (palaeolatitude: ~19°–27° N). The azimuth data of dune slip-faces reveal a bi-directional and oblique angular pattern that resembles the internal structures of modern longitudinal dunes. Based on the spatial pattern of slip-face directions and outcrop evidences, we suggest most of Lower Jurassic aeolian sandstones to be NNE–SSW- to NNW–SSE- oriented longitudinal dunes, which likely formed as the result of a combination of westerly, northwesterly, and northeasterly palaeo-winds. The reconstructed palaeo-wind pattern at ~19°–27° N appears to be consistent with the model-generated surface wind pattern and its seasonal turnover. The reconstructed palaeo-wind patterns also suggest an influence of orbitally induced changes in atmospheric pressure configuration in Pangaea.

scholarly journals Automated classification of the atmospheric circulation patterns that drive regional wave climates

2014 ◽  
Vol 14 (8) ◽  
pp. 2145-2155 ◽  
Author(s):  
J. Pringle ◽  
D. D. Stretch ◽  
A. Bárdossy
Keyword(s):  
Atmospheric Circulation ◽  
Low Pressure ◽  
Wave Climate ◽  
Automated Classification ◽  
Coastal Vulnerability ◽  
Extreme Wave ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Spatially Distributed ◽  
Wave Heights

Abstract. Wave climates are fundamental drivers of coastal vulnerability; changing trends in wave heights, periods and directions can severely impact a coastline. In a diverse storm environment, the changes in these parameters are difficult to detect and quantify. Since wave climates are linked to atmospheric circulation patterns, an automated and objective classification scheme was developed to explore links between synoptic-scale circulation patterns and wave climate variables, specifically wave heights. The algorithm uses a set of objective functions based on wave heights to guide the classification and find atmospheric classes with strong links to wave behaviour. Spatially distributed fuzzy numbers define the classes and are used to detect locally high- and low-pressure anomalies. Classes are derived through a process of simulated annealing. The optimized classification focuses on extreme wave events. The east coast of South Africa was used as a case study. The results show that three dominant patterns drive extreme wave events. The circulation patterns exhibit some seasonality with one pattern present throughout the year. Some 50–80% of the extreme wave events are explained by these three patterns. It is evident that strong low-pressure anomalies east of the country drive a wind towards the KwaZulu-Natal coastline which results in extreme wave conditions. We conclude that the methodology can be used to link circulation patterns to wave heights within a diverse storm environment. The circulation patterns agree with qualitative observations of wave climate drivers. There are applications to the assessment of coastal vulnerability and the management of coastlines worldwide.

scholarly journals Spring Extreme Precipitation Days in North China and Their Reliance on Atmospheric Circulation Patterns During 1979–2019

2022 ◽  
pp. 1-41
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
Extreme Precipitation ◽  
Interannual Variation ◽  
North China ◽  
Circulation Pattern ◽  
Southerly Wind ◽  
Atmospheric Circulation Patterns ◽  
Rain Gauges ◽  
Circulation Patterns

Abstract The interannual variation of springtime extreme precipitation (SEP) days in North China (NC) and their reliance on atmospheric circulation patterns are studied by using the continuous daily record of 396 rain gauges and the fifth generation of the European Centre for Medium-Range Weather Forecasts atmospheric reanalysis during 1979–2019. The SEP days are defined as the days when at least 10% of rain gauges in NC record daily precipitation no less than 10.5 mm. Results show that the number of SEP days shows large interannual variability but no significant trend in the study period. Using the objective classification method of the obliquely rotated principal analysis in T-mode, we classify the atmospheric circulation into five different patterns based on the geopotential height at 700 hPa. Three circulation patterns all have fronts and are associated with strong southerly wind, leading to 88% of SEP days in NC. The strong southerly wind may provide moisture and dynamic forcing for the frontal precipitation. The interannual variation of SEP days is related with the number of the three above-mentioned dominant circulation patterns. Further analysis shows that the West Pacific pattern could be one of the possible climate variability modes related to SEP days. This study reveals that the daily circulation pattern may be the linkage between SEP days and climate variability modes in NC.

scholarly journals Extreme Temperature Events in Serbia in Relation to Atmospheric Circulation

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1584
Author(s):  
Ivana Tošić ◽  
Suzana Putniković ◽  
Milica Tošić ◽  
Irida Lazić
Keyword(s):  
Atmospheric Circulation ◽  
Heat Waves ◽  
Extreme Temperature ◽  
Daily Maximum ◽  
Absolute Maximum ◽  
Extreme Temperature Events ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Maximum Temperatures ◽  
The Relationship

In this study, extremely warm and cold temperature events were examined based on daily maximum (Tx) and minimum (Tn) temperatures observed at 11 stations in Serbia during the period 1949–2018. Summer days (SU), warm days (Tx90), and heat waves (HWs) were calculated based on daily maximum temperatures, while frost days (FD) and cold nights (Tn10) were derived from daily minimum temperatures. Absolute maximum and minimum temperatures in Serbia rose but were statistically significant only for Tx in winter. Positive trends of summer and warm days, and negative trends of frost days and cold nights were found. A high number of warm events (SU, Tx90, and HWs) were recorded over the last 20 years. Multiple linear regression (MLR) models were applied to find the relationship between extreme temperature events and atmospheric circulation. Typical atmospheric circulation patterns, previously determined for Serbia, were used as predictor variables. It was found that MLR models gave the best results for Tx90, FD, and Tn10 in winter.

scholarly journals Aerosol reductions outweigh circulation changes for future improvements in Beijing haze

2021 ◽  
Author(s):  
Liang Guo ◽  
Laura J. Wilcox ◽  
Massimo Bollasina ◽  
Steven T. Turnock ◽  
Marianne T. Lund ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Atmospheric Circulation ◽  
Greenhouse Gas Emission ◽  
Weather Patterns ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Main Driver ◽  
Emission Changes ◽  
Aerosol Emissions ◽  
Circulation Changes

Abstract. Despite local emission reductions, severe haze events remain a serious issue in Beijing. Previous studies have suggested that both greenhouse gas increases and aerosol decreases are likely to increase the frequency of weather patterns conducive to haze events. However, the combined effect of atmospheric circulation changes and aerosol and precursor emission changes on Beijing haze remains unclear. We use the Shared Socioeconomic Pathways (SSPs) to explore the effects of aerosol and greenhouse gas emission changes on both haze weather and Beijing haze itself. We confirm that the occurrence of haze weather patterns is likely to increase in future under all SSPs, and show that even though aerosol reductions play a small role, greenhouse gas increases are the main driver, especially during the second half of the 21st century. However, the severity of the haze events decreases on decadal timescales by as much as 70 % by 2100. The main influence on the haze itself is the reductions in local aerosol emissions, which outweigh the effects of changes in atmospheric circulation patterns. This demonstrates that aerosol reductions are beneficial, despite their influence on the circulation.

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.

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