The Elementary Hadley Circulation

AbstractPrecipitation in the Three-River Headwater (TRH) region has undergone significant changes as a result of global warming, which can affect water resources in downstream regions of Asia. However, the underlying mechanisms of the precipitation variability during the cold season (October to April), are still not fully understood. In this study, the daily China gridded precipitation product of CN05.1 as well as the NCEP-NCAR reanalysis are used to investigate the characteristics of the cold season precipitation variability over the TRH region and associated atmospheric mechanisms. The cold season precipitation shows an increasing trend (5.5 mm decade-1) from 1961 to 2014, with a dry-to-wet shift in around the late 1980s. The results indicate that the increased precipitation is associated with the enhanced easterly anomalies over the Tibetan Plateau (TP) and enhanced southeasterly water vapor transport. The enhanced Walker circulations, caused by the gradients of sea surface temperature between the equatorial central-eastern Pacific and Indo-western Pacific in tropical oceans, resulted in strengthened easterly anomalies over the TP and the westward expansion of the anticyclone in the western North Pacific. Meanwhile, the changed Walker circulation is accompanied by a strengthened local Hadley circulation which leads to enhanced meridional water vapor transport from tropical oceans and the South China Sea toward the TRH region. Furthermore, the strengthened East Asia Subtropical Westerly jet may contribute to the enhanced divergence at upper level and anomalous ascending motion above the TRH region leading to more precipitation.

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Paleo-ENSO impacted habitat availability for early modern humans

10.5194/egusphere-egu21-8025 ◽

2021 ◽

Author(s):

Stefanie Kaboth-Bahr ◽

William D. Gosling ◽

Ralf Vogelsang ◽

André Bahr ◽

Eleanor M.L. Scerri ◽

...

Keyword(s):

Early Modern ◽

Hadley Circulation ◽

Low Latitude ◽

Proxy Records ◽

Western Africa ◽

Hominin Evolution ◽

Pan African ◽

African Climate ◽

Tight Correlation ◽

Evolution Of Vegetation

<p>In this study we synthesize terrestrial and marine proxy records spanning the last 620,000 years, to decipher pan-African climate variability, its drivers and potential linkages to hominin evolution. We find a tight correlation between moisture availability across Africa to Walker and Hadley Circulation variability that were most likely driven by changes in Earth&#180;s eccentricity. Our results demonstrate that low latitude insolation rather than glacial-interglacial cyclicity was the predominant driver of pan-African climate change during the mid to late Pleistocene. We argue that these low-latitude climate processes governed the dispersion and evolution of vegetation, as well as mammals, in eastern and western Africa, ultimately by increasing resource-rich and stable ecotonal settings that have long thought to have been the preferred habitats of hominins.</p>

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Global impact of smoke aerosols from landscape fires on climate and the Hadley circulation

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-5227-2013 ◽

2013 ◽

Vol 13 (10) ◽

pp. 5227-5241 ◽

Cited By ~ 86

Author(s):

M. G. Tosca ◽

J. T. Randerson ◽

C. S. Zender

Keyword(s):

Hadley Circulation ◽

Surface Radiation ◽

Climate Response ◽

Fire Emissions ◽

Aerosol Forcing ◽

Surface Temperatures ◽

Community Atmosphere Model ◽

Tropospheric Heating ◽

Aerosol Effects ◽

Global Precipitation

Abstract. Each year landscape fires across the globe emit black and organic carbon smoke particles that can last in the atmosphere for days to weeks. We characterized the climate response to these aerosols using an Earth system model. We used remote sensing observations of aerosol optical depth (AOD) and simulations from the Community Atmosphere Model, version 5 (CAM5) to optimize satellite-derived smoke emissions for high biomass burning regions. Subsequent global simulations using the adjusted fire emissions produced AODs that were in closer agreement with surface and space-based measurements. We then used CAM5, which included radiative aerosol effects, to evaluate the climate response to the fire-aerosol forcing. We conducted two 52 yr simulations, one with four sets of monthly cycling 1997–2009 fire emissions and one without. Fire emissions increased global mean annual AOD by 10% (+0.02) and decreased net all-sky surface radiation by 1% (1.3 W m−2). Elevated AODs reduced global surface temperatures by 0.13 &pm; 0.01 °C. Though global precipitation declined only slightly, patterns of precipitation changed, with large reductions near the Equator offset by smaller increases north and south of the intertropical convergence zone (ITCZ). A combination of increased tropospheric heating and reduced surface temperatures increased equatorial subsidence and weakened the Hadley circulation. As a consequence, precipitation decreased over tropical forests in South America, Africa and equatorial Asia. These results are consistent with the observed correlation between global temperatures and the strength of the Hadley circulation and studies linking tropospheric heating from black carbon aerosols with tropical expansion.

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Changes in the strength and width of the Hadley Circulation since 1871

Climate of the Past ◽

10.5194/cp-8-1169-2012 ◽

2012 ◽

Vol 8 (4) ◽

pp. 1169-1175 ◽

Cited By ~ 28

Author(s):

J. Liu ◽

M. Song ◽

Y. Hu ◽

X. Ren

Keyword(s):

20Th Century ◽

Global Climate ◽

Hadley Circulation ◽

Recent Change ◽

Early 20Th Century ◽

Greenhouse Warming ◽

Long Period ◽

The Past ◽

Period Oscillation

Abstract. Recent studies demonstrate that the Hadley Circulation has intensified and expanded for the past three decades, which has important implications for subtropical societies and may lead to profound changes in global climate. However, the robustness of this intensification and expansion that should be considered when interpreting long-term changes of the Hadley Circulation is still a matter of debate. It also remains largely unknown how the Hadley Circulation has evolved over longer periods. Here, we present long-term variability of the Hadley Circulation using the 20th Century Reanalysis. It shows a slight strengthening and widening of the Hadley Circulation since the late 1970s, which is not inconsistent with recent assessments. However, over centennial timescales (1871–2008), the Hadley Circulation shows a tendency towards a more intense and narrower state. More importantly, the width of the Hadley Circulation might have not yet completed a life-cycle since 1871. The strength and width of the Hadley Circulation during the late 19th to early 20th century show strong natural variability, exceeding variability that coincides with global warming in recent decades. These findings raise the question of whether the recent change in the Hadley Circulation is primarily attributed to greenhouse warming or to a long-period oscillation of the Hadley Circulation – substantially longer than that observed in previous studies.

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Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO<sub>2</sub> interhemispheric difference

10.5194/acp-2018-203 ◽

2018 ◽

Author(s):

Jorgen S. Frederiksen ◽

Roger J. Francey

Keyword(s):

Global Warming ◽

Hadley Circulation ◽

Co2 Concentration ◽

Transport Processes ◽

Boreal Summer ◽

Boreal Winter ◽

Advective Transport ◽

Interhemispheric Difference ◽

Eddy Transport ◽

The Difference

Abstract. The extreme El Niño of 2015 and 2016 coincided with record global warming and unprecedented strength of the Hadley circulation with significant impact on mean interhemispheric (IH) transport of CO2 and on the difference in CO2 concentration between Mauna Loa and Cape Grim (Cmlo-cgo). The relative roles of eddy transport and mean advective transport on IH CO2 annual differences from 1992 through to 2016 is explored. Eddy transport processes occur mainly in boreal winter-spring when Cmlo-cgo is large; an important component is due to Rossby wave generation by the Himalayas and propagation through the equatorial Pacific westerly duct generating and transmitting turbulent kinetic energy. Mean transport occurs mainly in boreal summer-autumn and varies with the strength of the Hadley circulation. The timing of annual changes in Cmlo-cgo is found to coincide well with dynamical indices that we introduce to characterize the transports. During the unrivalled 2009–2010 step in Cmlo-cgo indices of eddy and mean transport reinforce. In contrast for the 2015 to 2016 change in Cmlo-cgo the mean transport counteracts the eddy transport and the record strength of the Hadley circulation determines the annual IH CO2 difference. The interaction of increasing global warming and extreme El Niños may have important implications for altering the balance between eddy and mean IH CO2 transfer.

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Biomass Burning and Gas Flares Create the Extreme West African Aerosol Plume Which Perturbs the Hadley Circulation and Thereby Changes Europe’s Winter Climate

10.20944/preprints202108.0554.v2 ◽

2021 ◽

Author(s):

Keith A. Potts

Keyword(s):

High Pressure ◽

Biomass Burning ◽

Hadley Circulation ◽

West African ◽

Natural State ◽

Circulation System ◽

Winter Climate ◽

Gas Flaring ◽

The Uk ◽

Aerosol Plume

Three significant changes have occurred in the winter climate in Europe recently: increased UK flooding; Iberian drought; and warmer temperatures north of the Alps. The literature links all three to a persistent, significant increase in sea level pressure over Southern Europe, the Medi-terranean, Iberia and the Eastern Atlantic (SEMIEA) which changes the atmospheric circulation system: forcing cold fronts to the north away from Iberia; and creating a south westerly flow around the northern perimeter of the high-pressure region bringing warmer, moist air from the subtropical Atlantic to the UK and Europe which increases precipitation in the UK and raises the temperature in Europe. I use the Last Millennium Ensemble, MERRA-2 and Terra-NCEP data to demonstrate that the extreme, anthropogenic, West African aerosol Plume (WAP) which only exists from December to April perturbs the northern, regional Hadley Circulation creating the high pressure in the SEMIEA. I also show that the anthropogenic WAP has only existed in its extreme form in recent decades as the two major sources of the WAP aerosols: biomass burning; and gas flaring have both increased significantly since 1950 due to: a four-fold increase in population; and gas flaring rising from zero to 7.4 billion m3/annum and note that this time span coincides with the changes in the three elements of the winter climate of Europe. I also suggest that it may be possible to eliminate the WAP and return the winter climate of Europe to its natural state after the crucial first step of recognising the cause of the changes is taken.

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