scholarly journals Arctic autumn warming since 2002 dominated by changes in moisture modulated by multiple large-scale atmospheric circulations

2021 ◽  
pp. 105879
Author(s):  
Kailun Gao ◽  
Anmin Duan ◽  
Deliang Chen ◽  
Ji Wang ◽  
Bin Tang
Keyword(s):  
Large Scale ◽  
Atmospheric Circulations

scholarly journals Teleconnection between the Asian Polar Vortex and surface PM2.5 in China

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Lihua Zhou ◽  
Jing Zhang ◽  
Xiaohui Zheng ◽  
Siguang Zhu ◽  
Yueming Hu
Keyword(s):  
Large Scale ◽  
Meteorological Data ◽  
Fine Particulate Matter ◽  
Polar Vortex ◽  
Atmospheric Circulations ◽  
Fine Particulate ◽  
Heavy Pollution ◽  
Pollution Emissions ◽  
The Impact ◽  
East West

Abstract Atmospheric fine particulate matter (PM2.5) pollutions are of particular concern because of their direct and indirect harm to humans and organisms. China has suffered from severe air pollution for the past ten years, related to heavy pollution emissions and compounded by the effects of atmospheric circulation. This study applied statistical methods, observational data of ground pollutants, and meteorological data to analyze the impact of large-scale atmospheric circulations on PM2.5 pollution over China. Empirical orthogonal function (EOF) analysis was used to evaluate the main PM2.5 patterns and total contributions of the leading four EOFs. The results indicate that the total contributions of the leading four EOFs accounted for 50.5% of the total variance, reflecting four main types of PM2.5 pollution, namely, overall pollution phase, north–south phase, east–west phase and north–center–south phase, with contributions of 28.4%, 9.7%, 6.5% and 5.9%, respectively. We selected indices of the Asian Polar Vortex (APV) to analyze the impact of large-scale atmospheric circulations on PM2.5 pollution over China. The most pronounced APV control occurred in Beijing and its surroundings, specifically, along the Bohai Sea and the Northeast Plain.

scholarly journals Large-scale Climate Variability Footprint in Water Levels of Alluvial Aquifers Across Iran

2021 ◽  
Author(s):  
Abolfazl Rezaei
Keyword(s):  
Climate Variability ◽  
Large Scale ◽  
Southern Oscillation ◽  
Groundwater Resources ◽  
Water Levels ◽  
Climate Indices ◽  
Frequency Bands ◽  
Groundwater Levels ◽  
Aquifer Storage ◽  
Atmospheric Circulations

Abstract The ability to predict future variability of groundwater resources in time and space is of critical
importance in society’s adaptation to climate variability and change. Periodic control of large scale ocean-atmospheric circulations on groundwater levels proposes a potentially effective source of longer term forecasting capability. In this study, as a first national-scale assessment, we use the continues wavelet transform, global power spectrum, and wavelet coherence analyses to quantify the controls of the Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), and El Niño Southern Oscillation (ENSO) over the representative groundwater levels of the 24 principal aquifers, scattered across different 14 climate zones of Iran. The results demonstrate that aquifer storage variations are partially controlled by annual to interdecadal climate variability and are not solely a function of pumping variations. Moreover, teleconnections are observed to be both frequency and time specific. The significant coherence patterns between the climate indices and groundwater levels are observed at five frequency bands of the annual (~1-yr), interannual (2-4- and 4-6-yr), decadal (8-12-yr), and interdecadal (14-18yr), consistent with the dominant modes of climate indices. AMO’s strong footprint is observed at interdecadal and annual modes of groundwater levels while PDO’s highest imprint is seen in interannual, decadal, and interdecadal modes. The highest controlling influence of ENSO is observed across the decadal and interannual modes whereas the NAO’s footprint is marked at annual and interdecadal frequency bands. Further, it is observed that the groundwater variability being higher modulated by a combination of large-scale atmospheric circulations rather than each individual index. The decadal and interdecadal oscillation modes constitute the dominant modes in Iranian aquifers. Findings also mark the unsaturated zone contribution in damping and lagging of the climate variability modes, particularly for the higher frequency indices of ENSO and NAO where the groundwater variability is observed to be more correlated with lower frequent climate circulations such as PDO and AMO, rather than ENSO and NAO. Finally, it is found that the data length can significantly affect the teleconnections if the time series are not contemporaneous and only one value of coherence/correlation is computed for each particular series instead of separate computations for different frequency bands and different time spans.

Anthropogenic Aerosol Emissions and Rainfall Decline in Southwestern Australia: Coincidence or Causality?

2016 ◽  
Vol 29 (23) ◽  
pp. 8471-8493 ◽  
Author(s):  
Dominikus Heinzeller ◽  
Wolfgang Junkermann ◽  
Harald Kunstmann
Keyword(s):  
Twentieth Century ◽  
Large Scale ◽  
Anthropogenic Sources ◽  
Anthropogenic Factors ◽  
Gradual Decline ◽  
Anthropogenic Aerosol ◽  
Sudden Drop ◽  
Atmospheric Circulations ◽  
Southwestern Australia ◽  
Aerosol Emissions

Abstract It is commonly understood that the observed decline in precipitation in southwestern Australia during the twentieth century is caused by anthropogenic factors. Candidates therefore are changes to large-scale atmospheric circulations due to global warming, extensive deforestation, and anthropogenic aerosol emissions—all of which are effective on different spatial and temporal scales. This contribution focuses on the role of rapidly rising aerosol emissions from anthropogenic sources in southwestern Australia around 1970. An analysis of historical long-term rainfall data of the Bureau of Meteorology shows that southwestern Australia as a whole experienced a gradual decline in precipitation over the twentieth century. However, on smaller scales and for the particular example of the Perth catchment area, a sudden drop in precipitation around 1970 is apparent. Modeling experiments at a convection-resolving resolution of 3.3 km using the Weather Research and Forecasting (WRF) Model version 3.6.1 with the aerosol-aware Thompson–Eidhammer microphysics scheme are conducted for the period 1970–74. A comparison of four runs with different prescribed aerosol emissions and without aerosol effects demonstrates that tripling the pre-1960s atmospheric CCN and IN concentrations can suppress precipitation by 2%–9%, depending on the area and the season. This suggests that a combination of all three processes is required to account for the gradual decline in rainfall seen for greater southwestern Australia and for the sudden drop observed in areas along the west coast in the 1970s: changing atmospheric circulations, deforestation, and anthropogenic aerosol emissions.

Spatial variability of trends in hydrological extremes induced by orographically enhanced rainfall events due to westerly atmospheric circulations

2005 ◽  
Vol 51 (5) ◽  
pp. 15-21 ◽  
Author(s):  
L. Pfister ◽  
G. Drogue ◽  
C. Poirier ◽  
L. Hoffmann
Keyword(s):  
Spatial Variability ◽  
Large Scale ◽  
Direct Consequence ◽  
Positive Trend ◽  
Winter Rainfall ◽  
Atmospheric Circulations ◽  
Hydrological Extremes ◽  
Mosel River ◽  
The One ◽  
Spatially Varying

Since the mid 1970s, the number of days with westerly atmospheric circulations has strongly increased during winter months. As a consequence, rainfall totals, rainfall event duration and intensity have been subject to significant positive trends throughout the Mosel river basin. However, the trends identified through the non-parametrical test named Kendall's tau have shown to be spatially varying. The intensity of the trends appears to be directly linked to orographic obstacles that are well known to have a strong influence on average rainfall totals. A direct consequence of the changes having affected winter rainfall under westerly atmospheric circulations on the one hand and the spatial variability of these changes on the other hand, is a spatially varying positive trend in maximum winter streamflow. Thus, even though a clear large-scale change has affected winter rainfall over the past decades, its intensity is either strongly moderated or enhanced by orographic obstacles. The related changes in streamflow are directly dependent on the spatial variability of the changed rainfall characteristics.

Relative contributions of internal atmospheric variability and surface processes to the interannual variations in wintertime Arctic surface air temperatures

2021 ◽  
pp. 1-48
Author(s):  
Fengmin Wu ◽  
Wenkai Li ◽  
Peng Zhang ◽  
Wei Li
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Surface Air Temperature ◽  
Surface Processes ◽  
The Arctic ◽  
Interannual Variations ◽  
Atmospheric Variability ◽  
Near Surface ◽  
Atmospheric Circulations ◽  
Downward Longwave Radiation

AbstractSuperimposed on a warming trend, Arctic winter surface air temperature (SAT) exhibits substantial interannual variability, whose underlying mechanisms are unclear, especially regarding the role of sea-ice variations and atmospheric processes. Here, atmospheric reanalysis data and idealized atmospheric model simulations are used to reveal the mechanisms by which sea-ice variations and atmospheric anomalous conditions affect interannual variations in wintertime Arctic SAT. Results show that near-surface interannual warming in the Arctic is accompanied by comparable warming throughout large parts of the Arctic troposphere and large-scale anomalous atmospheric circulation patterns. Within the Arctic, changes in large-scale atmospheric circulations due to internal atmospheric variability explain a substantial fraction of interannual variation in SAT and tropospheric temperatures, which lead to an increase in moisture and downward longwave radiation, with the rest likely coming from sea ice-related and other surface processes. Arctic winter sea-ice loss allows the ocean to release more heat and moisture, which enhances Arctic warming; however, this effect on SAT is confined to the ice-retreat area and has a limited influence on large-scale atmospheric circulations.

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