Evolution of the Distribution of Upper-Tropospheric Humidity over the Indian Ocean: Connection with Large-Scale Advection and Local Cloudiness

AbstractThe spatial and temporal distribution of upper-tropospheric humidity (UTH) observed by the Sounder for Atmospheric Profiling of Humidity in the Intertropics by Radiometry (SAPHIR)/Megha-Tropiques radiometer is analyzed over two subregions of the Indian Ocean during October–December over 2011–14. The properties of the distribution of UTH were studied with regard to the phase of the Madden–Julian oscillation (active or suppressed) and large-scale advection versus local production of moisture. To address these topics, first, a Lagrangian back-trajectory transport model was used to assess the role of the large-scale transport of air masses in the intraseasonal variability of UTH. Second, the temporal evolution of the distribution of UTH is analyzed using the computation of the higher moments of its probability distribution function (PDF) defined for each time step over the domain. The results highlight significant differences in the PDF of UTH depending on the phase of the MJO. The modeled trajectories ending in the considered domain originate from an area that strongly varies depending on the phases of the MJO: during the active phases, the air masses are spatially constrained within the tropical Indian Ocean domain, whereas a distinct upper-tropospheric (200–150 hPa) westerly flow guides the intraseasonal variability of UTH during the suppressed phases. Statistical relationships between the cloud fractions and the UTH PDF moments of are found to be very similar regardless of the convective activity. However, the occurrence of thin cirrus clouds is associated with a drying of the upper troposphere (enhanced during suppressed phases), whereas the occurrence of thick cirrus anvil clouds appears to be significantly related to a moistening of the upper troposphere.

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Distinctive Roles of Air–Sea Coupling on Different MJO Events: A New Perspective Revealed from the DYNAMO/CINDY Field Campaign*

Monthly Weather Review ◽

10.1175/mwr-d-14-00221.1 ◽

2015 ◽

Vol 143 (3) ◽

pp. 794-812 ◽

Cited By ~ 31

Author(s):

Xiouhua Fu ◽

Wanqiu Wang ◽

June-Yi Lee ◽

Bin Wang ◽

Kazuyoshi Kikuchi ◽

...

Keyword(s):

Indian Ocean ◽

Large Scale ◽

Essential Role ◽

Intraseasonal Variability ◽

Physical Processes ◽

Field Campaign ◽

Strongly Coupled ◽

The Indian Ocean ◽

New Perspective ◽

Sst Anomalies

Abstract Previous observational analysis and modeling studies indicate that air–sea coupling plays an essential role in improving MJO simulations and extending MJO forecasting skills. However, whether the SST feedback plays an indispensable role for the existence of the MJO remains controversial, and the precise physical processes through which the SST feedback may lead to better MJO simulations and forecasts remain elusive. The DYNAMO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY) field campaign recently completed over the Indian Ocean reveals a new perspective and provides better data to improve understanding of the MJO. It is found that among the five MJO events that occurred during the DYNAMO/CINDY field campaign, only two MJO events (the November and March ones) have robust SST anomalies associated with them. For the other three MJO events (the October, December, and January ones), no coherent SST anomalies are observed. This observational scenario suggests that the roles of air–sea coupling on the MJO vary greatly from event to event. To elucidate the varying roles of air–sea coupling on different MJO events, a suite of hindcast experiments was conducted with a particular focus on the October and November MJO events. The numerical results confirm that the October MJO is largely controlled by atmospheric internal dynamics, while the November MJO is strongly coupled with underlying ocean. For the November MJO event, the positive SST anomalies significantly improve MJO forecasting by enhancing the response of a Kelvin–Rossby wave couplet, which prolongs the feedback between convection and large-scale circulations, and thus favors the development of stratiform rainfall, in turn, facilitating the production of eddy available potential energy and significantly amplifying the intensity of the model November MJO.

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Transport pathways of CO in the African upper troposphere during the monsoon season: a study based upon the assimilation of spaceborne observations

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-3231-2008 ◽

2008 ◽

Vol 8 (12) ◽

pp. 3231-3246 ◽

Cited By ~ 74

Author(s):

B. Barret ◽

P. Ricaud ◽

C. Mari ◽

J.-L. Attié ◽

N. Bousserez ◽

...

Keyword(s):

Southeast Asia ◽

Southern Africa ◽

Large Scale ◽

Transport Model ◽

Hadley Cell ◽

High Time Resolution ◽

Transport Pathways ◽

Air Masses ◽

Upper Troposphere ◽

African Monsoon

Abstract. The transport pathways of carbon monoxide (CO) in the African Upper Troposphere (UT) during the West African Monsoon (WAM) is investigated through the assimilation of CO observations by the Aura Microwave Limb Sounder (MLS) in the MOCAGE Chemistry Transport Model (CTM). The assimilation setup, based on a 3-D First Guess at Assimilation Time (3-D-FGAT) variational method is described. Comparisons between the assimilated CO fields and in situ airborne observations from the MOZAIC program between Europe and both Southern Africa and Southeast Asia show an overall good agreement around the lowermost pressure level sampled by MLS (~215 hPa). The 4-D assimilated fields averaged over the month of July 2006 have been used to determine the main dynamical processes responsible for the transport of CO in the African UT. The studied period corresponds to the second AMMA (African Monsoon Multidisciplinary Analyses) aircraft campaign. At 220 hPa, the CO distribution is characterized by a latitudinal maximum around 5° N mostly driven by convective uplift of air masses impacted by biomass burning from Southern Africa, uplifted within the WAM region and vented predominantly southward by the upper branch of the winter hemisphere Hadley cell. Above 150 hPa, the African CO distribution is characterized by a broad maximum over northern Africa. This maximum is mostly controlled by the large scale UT circulation driven by the Asian Summer Monsoon (ASM) and characterized by the Asian Monsoon Anticyclone (AMA) centered at 30° N and the Tropical Easterly Jet (TEJ) on the southern flank of the anticyclone. Asian pollution uplifted to the UT over large region of Southeast Asia is trapped within the AMA and transported by the anticyclonic circulation over Northeast Africa. South of the AMA, the TEJ is responsible for the tranport of CO-enriched air masses from India and Southeast Asia over Africa. Using the high time resolution provided by the 4-D assimilated fields, we give evidence that the variability of the African CO distribution above 150 hPa and north of the WAM region is mainly driven by the synoptic dynamical variability of both the AMA and the TEJ.

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Transport pathways of CO in the African upper troposphere during the monsoon season: a study based upon the assimilation of spaceborne observations

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-2863-2008 ◽

2008 ◽

Vol 8 (1) ◽

pp. 2863-2902 ◽

Cited By ~ 1

Author(s):

B. Barret ◽

P. Ricaud ◽

C. Mari ◽

J.-L. Attié ◽

N. Bousserez ◽

...

Keyword(s):

Southeast Asia ◽

Southern Africa ◽

Large Scale ◽

Transport Model ◽

Hadley Cell ◽

High Time Resolution ◽

Transport Pathways ◽

Air Masses ◽

Upper Troposphere ◽

African Monsoon

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Atmospheric pollutant outflow from southern Asia: a review

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-11017-2010 ◽

2010 ◽

Vol 10 (22) ◽

pp. 11017-11096 ◽

Cited By ~ 302

Author(s):

M. G. Lawrence ◽

J. Lelieveld

Keyword(s):

Indian Ocean ◽

Large Scale ◽

Hydrological Cycle ◽

Scale Effects ◽

Long Distance ◽

Atmospheric Pollutant ◽

Near Surface ◽

Air Masses ◽

Southern Asia ◽

The Indian Ocean

Abstract. Southern Asia, extending from Pakistan and Afghanistan to Indonesia and Papua New Guinea, is one of the most heavily populated regions of the world. Biofuel and biomass burning play a disproportionately large role in the emissions of most key pollutant gases and aerosols there, in contrast to much of the rest of the Northern Hemisphere, where fossil fuel burning and industrial processes tend to dominate. This results in polluted air masses which are enriched in carbon-containing aerosols, carbon monoxide, and hydrocarbons. The outflow and long-distance transport of these polluted air masses is characterized by three distinct seasonal circulation patterns: the winter monsoon, the summer monsoon, and the monsoon transition periods. During winter, the near-surface flow is mostly northeasterly, and the regional pollution forms a thick haze layer in the lower troposphere which spreads out over millions of square km between southern Asia and the Intertropical Convergence Zone (ITCZ), located several degrees south of the equator over the Indian Ocean during this period. During summer, the heavy monsoon rains effectively remove soluble gases and aerosols. Less soluble species, on the other hand, are lifted to the upper troposphere in deep convective clouds, and are then transported away from the region by strong upper tropospheric winds, particularly towards northern Africa and the Mediterranean in the tropical easterly jet. Part of the pollution can reach the tropical tropopause layer, the gateway to the stratosphere. During the monsoon transition periods, the flow across the Indian Ocean is primarily zonal, and strong pollution plumes originating from both southeastern Asia and from Africa spread across the central Indian Ocean. This paper provides a review of the current state of knowledge based on the many observational and modeling studies over the last decades that have examined the southern Asian atmospheric pollutant outflow and its large scale effects. An outlook is provided as a guideline for future research, pointing out particularly critical issues such as: resolving discrepancies between top down and bottom up emissions estimates; assessing the processing and aging of the pollutant outflow; developing a better understanding of the observed elevated pollutant layers and their relationship to local sea breeze and large scale monsoon circulations; and determining the impacts of the pollutant outflow on the Asian monsoon meteorology and the regional hydrological cycle, in particular the mountain cryospheric reservoirs and the fresh water supply, which in turn directly impact the lives of over a billion inhabitants of southern Asia.

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Large-Scale Distinctions between MJO and Non-MJO Convective Initiation over the Tropical Indian Ocean

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-13-029.1 ◽

2013 ◽

Vol 70 (9) ◽

pp. 2696-2712 ◽

Cited By ~ 42

Author(s):

Jian Ling ◽

Chidong Zhang ◽

Peter Bechtold

Keyword(s):

Indian Ocean ◽

Large Scale ◽

Tropical Indian Ocean ◽

Negative Temperature ◽

Maritime Continent ◽

Zonal Structure ◽

Convective Initiation ◽

Upper Troposphere ◽

The Indian Ocean ◽

Pressure Surge

Abstract In this study, the authors seek large-scale signals that may distinguish MJO from non-MJO convective events before they start over the Indian Ocean. Three such signals were found. Low-level easterly anomalies extend from the surface to the midtroposphere and move from the western to eastern Indian Ocean. Surface pressure anomalies exhibit a zonal structure of wavenumber 1 with an equatorial low-pressure surge penetrating eastward from Africa through the Indian Ocean and reaching the Maritime Continent. Negative temperature anomalies in the middle to upper troposphere start over the Indian Ocean and move eastward. All of them emerge 20 days before convective initiation of the MJO and move eastward at speeds close to that of the MJO without any direct connection to MJO convection. They are not obviously related to the extratropics in any discernible way or any preceding MJO events. They are absent in non-MJO convective events. These signals provide useful information for forecasting MJO initiation over the Indian Ocean. They can be signatures of a dry dynamics mode of the MJO, if it exists.

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Exploring the ionic composition of the Asian Tropopause Aerosol Layer using medium duration balloon flights

10.5194/egusphere-egu21-2323 ◽

2021 ◽

Author(s):

Hazel Vernier ◽

Neeraj Rastogi ◽

Hongyu Liu ◽

Duncan Fairlie ◽

Amit Pandit ◽

...

Keyword(s):

Particle Size ◽

Large Scale ◽

Transport Model ◽

Large Fraction ◽

Ionic Composition ◽

Back Trajectory ◽

Aerosol Layer ◽

Air Mass ◽

Air Masses ◽

Model Simulations

Satellite observations have revealed an enhanced aerosol layer near the tropopause over Asia during the summer monsoon, called the Asian Tropopause Aerosol Layer (ATAL). The chemical composition of the ATAL is investigated here using offline ionic analysis of aerosols collected with a balloon-borne impactor near the tropopause region over India onboard extended duration balloon flights in the summer of 2017 and winter 2018. We found NO3- and NO2- dominant among other ions with values ranging between 87-343 ng/m3 during the summer campaign. In contrast, SO4 levels were found above detection limit (>10 ng/m3) only in winter. In addition, we determined the origin of the air masses sampled during the flights through back trajectory analysis combined with convection. The results obtained therein were put into a context of large-scale transport and aerosol distribution with GEOS-Chem chemical transport model simulations. The first flight of summer 2017 sampled air mass within the Asian monsoon anticyclone (AMA), associated with smaller particle size found on stage 2 (particle size cut off > 0.15 microns) of the impactor, while the second flight sampled air mass at the edge of the AMA associated with larger particle size on stage 1 (particle size cut off between 2 and 0.5 microns). The sampled air masses in winter 2018 were affected by smoke from the Pacific Northwest fire event in Canada, which occurred 7 months prior to our campaign. Concentrations of SO42-, NH4+, and Ca2+ were enhanced. Overall, our results suggest that nitrogen- containing particles represent a large fraction of aerosols populating the ATAL in agreement with aircraft measurements during the StratoClim campaign. Furthermore, GEOS-chem model simulations suggest that lightning NOx emissions had a minimal impact on the production of nitrate aerosols sampled during the two flights.&#160;

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The Role of Atmospheric Processes Associated with Hurricane Olga in the December 2001 Floods in Israel

Journal of Hydrometeorology ◽

10.1175/jhm-399.1 ◽

2004 ◽

Vol 5 (6) ◽

pp. 1259-1270 ◽

Cited By ~ 35

Author(s):

Simon O. Krichak ◽

Pinhas Alpert ◽

Melina Dayan

Keyword(s):

Large Scale ◽

Western Europe ◽

Narrow Band ◽

Eastern Mediterranean ◽

Tropical Storm ◽

Back Trajectory ◽

Simulation Experiments ◽

Air Masses ◽

Upper Troposphere

Abstract Over the period from 0000 UTC 3 December to 0000 UTC 5 December 2001, heavy rains fell in northern Israel. Intensity of the rainfall in some areas exceeded 250 mm (24 h)−1. Results of an investigation of the case including back-trajectory evaluations, numerical simulation experiments, and a potential vorticity (PV) analysis are presented. It is demonstrated that the unusual eastern Mediterranean process has been initiated by the formation of a tropical storm that later became Hurricane Olga from 25 to 29 November. The consequent synoptic processes were associated with the development of a large-scale anticyclone to the NE of the tropical storm. Large-scale subsidence in the anticyclone played a central role in the process by leading to a convergence of the moist air masses in a narrow band on the outskirts of the system. The air masses from the area were later transported into the midtroposphere over western Europe. The interaction of these relatively warm and wet air masses with the cold and dry upper-tropospheric air over Europe has led to an intensification of the upper-tropospheric northerly airflow, extrusion of stratospheric air into the upper troposphere, and formation of a PV streamer system over southern Europe. Finally, the positioning and intensity of the PV streamer, as well as the large amounts of air moisture over the Mediterranean region, contributed to the intensity of the 3–5 December 2001 torrential rains over Israel.

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Subsurface Fluxes Beneath Large-Scale Convective Centers in the Indian Ocean: Coupled Air-Wave-Sea Processes in the Subtropics

10.21236/ada574114 ◽

2012 ◽

Author(s):

James N. Moum

Keyword(s):

Indian Ocean ◽

Large Scale ◽

The Indian Ocean

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Analysis of a rapid increase of stratospheric ozone during late austral summer 2008 over Kerguelen (49.4° S, 70.3° E)

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-363-2011 ◽

2011 ◽

Vol 11 (1) ◽

pp. 363-373 ◽

Cited By ~ 10

Author(s):

H. Bencherif ◽

L. El Amraoui ◽

G. Kirgis ◽

J. Leclair De Bellevue ◽

A. Hauchecorne ◽

...

Keyword(s):

Potential Vorticity ◽

Large Scale ◽

Lower Stratosphere ◽

Transport Model ◽

Stratospheric Ozone ◽

Three Dimensional ◽

Austral Summer ◽

Air Masses ◽

Global Mapping ◽

The Tropics

Abstract. This paper reports on an increase of ozone event observed over Kerguelen (49.4° S, 70.3° E) in relationship with large-scale isentropic transport. This is evidenced by ground-based observations (co-localised radiosonde and SAOZ experiments) together with satellite global observations (Aura/MLS) assimilated into MOCAGE, a Méteo-France model. The study is based on the analyses of the first ozonesonde experiment never recorded at the Kerguelen site within the framework of a French campaign called ROCK that took place from April to August 2008. Comparisons and interpretations of the observed event are supported by co-localised SAOZ observations, by global mapping of tracers (O3, N2O and columns of O3) from Aura/MLS and Aura/OMI experiments, and by model simulations of Ertel Potential Vorticity initialised by the ECMWF (European Centre for Medium-Range Weather Forecasts) data reanalyses. Satellite and ground-based observational data revealed a consistent increase of ozone in the local stratosphere by mid-April 2008. Additionally, Ozone (O3) and nitrous oxide (N2O) profiles obtained during January–May 2008 using the Microwave Limb Sounder (MLS) aboard the Aura satellite are assimilated into MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle), a global three-dimensional chemistry transport model of Météo-France. The assimilated total O3 values are consistent with SAOZ ground observations (within ±5%), and isentropic distributions of O3 match well with maps of advected potential vorticity (APV) derived from the MIMOSA model, a high-resolution advection transport model, and from the ECMWF reanalysis. The event studied seems to be related to the isentropic transport of air masses that took place simultaneously in the lower- and middle-stratosphere, respectively from the polar region and from the tropics to the mid-latitudes. In fact, the ozone increase observed by mid April 2008 resulted simultaneously: (1) from an equator-ward departure of polar air masses characterised with a high-ozone layer in the lower stratosphere (near the 475 K isentropic level), and (2) from a reverse isentropic transport from the tropics to mid- and high-latitudes in the upper stratosphere (nearby the 700 K level). The increase of ozone observed over Kerguelen from the 16-April ozonesonde profile is thus attributed to a concomitant isentropic transport of ozone in two stratospheric layers: the tropical air moving southward and reaching over Kerguelen in the upper stratosphere, and the polar air passing over the same area but in the lower stratosphere.

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Modeling the transport of very short-lived substances into the tropical upper troposphere and lower stratosphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-18511-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 18511-18543 ◽

Cited By ~ 2

Author(s):

J. Aschmann ◽

B. M. Sinnhuber ◽

E. L. Atlas ◽

S. M. Schauffler

Keyword(s):

Large Scale ◽

Lower Stratosphere ◽

Transport Model ◽

Three Dimensional ◽

Chemical Transport Model ◽

Heating Rates ◽

Model Calculations ◽

Upper Troposphere ◽

Mass Fluxes ◽

Tropical Upper Troposphere

Abstract. The transport of very short-lived substances into the tropical upper troposphere and lower stratosphere is investigated by a three-dimensional chemical transport model using archived convective updraft mass fluxes (or detrainment rates) from the European Centre for Medium-Range Weather Forecast's ERA-Interim reanalysis. Large-scale vertical velocities are calculated from diabatic heating rates. With this approach we explicitly model the large scale subsidence in the tropical troposphere with convection taking place in fast and isolated updraft events. The model calculations agree generally well with observations of bromoform and methyl iodide from aircraft campaigns and with ozone and water vapor from sonde and satellite observations. Using a simplified treatment of dehydration and bromine product gas washout we give a range of 1.6 to 3 ppt for the contribution of bromoform to stratospheric bromine, assuming a uniform source in the boundary layer of 1 ppt. We show that the most effective region for VSLS transport into the stratosphere is the West Pacific, accounting for about 55% of the bromine from bromoform transported into the stratosphere under the supposition of a uniformly distributed source.

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