scholarly journals In Situ Observations of Light‐Absorbing Carbonaceous Aerosols at Himalaya: Analysis of the South Asian Sources and Trans‐Himalayan Valleys Transport Pathways

2020 ◽  
Vol 125 (18) ◽  
Author(s):  
Qi Yuan ◽  
Xin Wan ◽  
Zhiyuan Cong ◽  
Mengmeng Li ◽  
Lei Liu ◽  
...  
Keyword(s):  
South Asian ◽  
Carbonaceous Aerosols ◽  
The South ◽  
Transport Pathways ◽  
In Situ Observations

scholarly journals Upper tropospheric CH<sub>4</sub> and CO affected by the South Asian summer monsoon during OMO

2018 ◽  
Author(s):  
Laura Tomsche ◽  
Andrea Pozzer ◽  
Narendra Ojha ◽  
Uwe Parchatka ◽  
Jos Lelieveld ◽  
...  
Keyword(s):  
South Asian ◽  
Asian Summer Monsoon ◽  
Trace Gases ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Transport Pathways ◽  
Air Masses ◽  
Upper Troposphere ◽  
Asian Summer

Abstract. The Asian monsoon anticyclone (AMA) is a yearly recurring phenomenon in the northern hemispheric upper troposphere and lower stratosphere. It is connected to the South Asian summer monsoon, and the circulation extends approximately across 20°–120° E and 15°–40° N longitude-latitude. It has a clearly observable signature due to vertical transport of polluted air masses from the surface to the upper troposphere by the monsoon convection. However, the transport pathways and the fate of pollutants in the upper troposphere are not yet fully understood. As pollution emissions in South Asia are increasing, changes in the chemical composition of the AMA can be expected. We performed in situ measurements of carbon monoxide (CO) and methane (CH4) in the region of monsoon outflow and in background air in the upper troposphere (Mediterranean, Arabian Peninsula, Arabian Sea) by optical absorption spectroscopy on board the German High Altitude and Long range (HALO) research aircraft during the OMO (Oxidation Mechanism Observations) mission in summer 2015. We identified the transport pathways and the origin of the trace gases with back trajectories, calculated with the Lagrangian particle dispersion model FLEXPART, and we compared the in situ data with simulations of the atmospheric chemistry general circulation model EMAC. CH4 and CO mixing ratios were found to be enhanced within the AMA, on average by 72.1 ppb and 20.1 ppb, respectively, originating in the South Asian region (Indio-Gangetic Plain, North East India, Bangladesh and Bay of Bengal). It appears that CH4 is an ideal monsoon tracer in the upper troposphere due to its extended lifetime and the strong South Asian emissions. Furthermore, we used the measurements and model results to study the dynamics of the AMA, with an emphasis on the southern and western areas within the upper troposphere. For example, we distinguished four AMA modes based on different meteorological conditions. During one occasion we observed that under the influence of dwindling flow the transport barrier between the anticyclone and its surroundings weakened, expelling air masses from the AMA. The trace gases exhibited a distinct fingerprint of the AMA, and we also found that CH4 accumulated over the course of the OMO campaign.

scholarly journals An algorithm for detecting <i>Trichodesmium</i> surface blooms in the South Western Tropical Pacific

2011 ◽  
Vol 8 (3) ◽  
pp. 5653-5689 ◽  
Author(s):  
C. Dupouy ◽  
D. Benielli-Gary ◽  
J. Neveux ◽  
Y. Dandonneau ◽  
T. K. Westberry
Keyword(s):  
Total Surface Area ◽  
Tropical Pacific ◽  
The South ◽  
Western Tropical Pacific ◽  
Tropical Oceans ◽  
Novel Approach ◽  
Monthly Distribution ◽  
C And N ◽  
In Situ Observations

Abstract. Trichodesmium, a major colonial cyanobacterial nitrogen fixer, forms large blooms in NO3-depleted tropical oceans and enhances CO2 sequestration by the ocean due to its ability to fix dissolved dinitrogen. Thus, its importance in C and N cycles requires better estimates of its distribution at basin to global scales. However, existing algorithms to detect them from satellite have not yet been successful in the South Western Tropical Pacific (SWTP). Here, a novel approach based on radiance anomaly spectra (RAS) observed in SeaWiFS imagery is used to detect Trichodesmium during the austral summertime in the SWTP. Selected pixels are characterized by a restricted range of parameters quantifying RAS spectra quantitative parameters (e.g. slope, intercept, curvature). The fraction of valid pixels identified as Trichodesmium surface blooms in the region 5° S–25° S 160° E–190° E is low (between 0.01 and 0.2 %), but is about 100 times higher than suggested by previous algorithms. This represents a total surface area which varies from 1500 to 20 000 km2. A monthly distribution of Trichodesmium surface accumulations in the SWTP is presented which demonstrates that the number of selected pixels peaks in November–February each year, consistent with field observations. This approach was validated with in situ observations of Trichodesmium surface accumulations for the period 1998–2010.

scholarly journals The Energy Budget of the Polar Atmosphere in MERRA

2012 ◽  
Vol 25 (1) ◽  
pp. 5-24 ◽  
Author(s):  
Richard I. Cullather ◽  
Michael G. Bosilovich
Keyword(s):  
Energy Budget ◽  
The Arctic ◽  
Polar Regions ◽  
Polar Cap ◽  
The South ◽  
Atmospheric Energy ◽  
In Situ Observations ◽  
Energy Convergence ◽  
South Polar

Abstract Components of the atmospheric energy budget from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) are evaluated in polar regions for the period 1979–2005 and compared with previous estimates, in situ observations, and contemporary reanalyses. Closure of the budget is reflected by the analysis increments term, which indicates an energy surplus of 11 W m−2 over the North Polar cap (70°–90°N) and 22 W m−2 over the South Polar cap (70°–90°S). Total atmospheric energy convergence from MERRA compares favorably with previous studies for northern high latitudes but exceeds the available previous estimate for the South Polar cap by 46%. Discrepancies with the Southern Hemisphere energy transport are largest in autumn and may be related to differences in topography with earlier reanalyses. For the Arctic, differences between MERRA and other sources in top of atmosphere (TOA) and surface radiative fluxes are largest in May. These differences are concurrent with the largest discrepancies between MERRA parameterized and observed surface albedo. For May, in situ observations of the upwelling shortwave flux in the Arctic are 80 W m−2 larger than MERRA, while the MERRA downwelling longwave flux is underestimated by 12 W m−2 throughout the year. Over grounded ice sheets, the annual mean net surface energy flux in MERRA is erroneously nonzero. Contemporary reanalyses from the Climate Forecast Center (CFSR) and the Interim Re-Analyses of the European Centre for Medium-Range Weather Forecasts (ERA-I) are found to have better surface parameterizations; however, these reanalyses also disagree with observed surface and TOA energy fluxes. Discrepancies among available reanalyses underscore the challenge of reproducing credible estimates of the atmospheric energy budget in polar regions.

scholarly journals Remote Sensing of <i>Trichodesmium</i> spp. mats in the Western Tropical South Pacific

2018 ◽  
Author(s):  
Guillaume Rousset ◽  
Florian De Boissieu ◽  
Christophe E. Menkes ◽  
Jérôme Lefèvre ◽  
Robert Frouin ◽  
...  
Keyword(s):  
Large Scale ◽  
New Caledonia ◽  
Regional Scale ◽  
Atmospheric Correction ◽  
South Pacific ◽  
The South ◽  
False Positive Detection ◽  
Modis Imagery ◽  
In Situ Observations

Abstract. Trichodesmium is the main nitrogen-fixing species in the South Pacific region, a hotspot for diazotrophy. Due to the paucity of in situ observations, methods for detecting Trichodesmium presence on a large scale have been investigated to assess the regional-to-global impact of these species on primary production and carbon cycling. A number of satellite-derived algorithms have been developed to identify Trichodesmium surface blooms, but determining with confidence their accuracy has been difficult, chiefly because of the scarcity of sea-truth information at time of satellite overpass. Here, we use a series of new cruises as well as airborne observational surveys in the South Pacific to quantify statistically the ability of these algorithms to discern correctly Trichodesmium surface blooms in the satellite imagery. The evaluation, performed on MODIS data at 250 m and 1 km resolution acquired over the South West Pacific, shows limitations due to spatial resolution, clouds, and atmospheric correction. A new satellite-based algorithm is designed to alleviate some of these limitations, by exploiting optimally spectral features in the atmospherically corrected reflectance at 531, 645, 678, 748, and 869 nm. This algorithm outperforms former ones near clouds, limiting false positive detection, and allowing regional scale automation. Compared with observations, 80 % of the detected mats are within a 2 km range, demonstrating the good statistical skill of the new algorithm. Application to MODIS imagery acquired during the February–March 2015 OUTPACE campaign reveals the presence of surface blooms Northwest and East of New Caledonia and near 20° S–172° W in qualitative agreement with measured nitrogen fixation rates. The new algorithm, however, fails to detect sub-surface booms evidenced in trichome counts. Improving Trichodesmium detection requires measuring ocean color at higher spectral and spatial (

scholarly journals Upper tropospheric CH<sub>4</sub> and CO affected by the South Asian summer monsoon during the Oxidation Mechanism Observations mission

2019 ◽  
Vol 19 (3) ◽  
pp. 1915-1939 ◽  
Author(s):  
Laura Tomsche ◽  
Andrea Pozzer ◽  
Narendra Ojha ◽  
Uwe Parchatka ◽  
Jos Lelieveld ◽  
...  
Keyword(s):  
South Asian ◽  
Asian Summer Monsoon ◽  
Oxidation Mechanism ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Air Masses ◽  
Upper Troposphere ◽  
In Situ Data ◽  
Asian Summer

Abstract. The Asian monsoon anticyclone (AMA) is annual phenomenon in the northern hemispheric upper troposphere and lower stratosphere. It is part of the South Asian summer monsoon system, and it has a clearly observable signature due to the vertical transport of polluted air masses from the surface to the upper troposphere by monsoon convection. We performed in situ measurements of carbon monoxide (CO) and methane (CH4) in the region of monsoon outflow and in background air in the upper troposphere (Mediterranean, Arabian Peninsula, and Arabian Sea) using optical absorption spectroscopy on board the High Altitude and LOng range (HALO) research aircraft during the OMO (Oxidation Mechanism Observations) mission in summer 2015. We identified the transport pathways and the origin of the trace gases with back trajectories, which were calculated using the Lagrangian particle dispersion model FLEXPART, and we compared the in situ data with simulations of the atmospheric chemistry general circulation model EMAC. CH4 and CO mixing ratios were found to be enhanced within the AMA, the in situ data increased by 72.1 and 20.1 ppbv on average, respectively, and originated in the South Asian region (Indo-Gangetic Plain, northeastern India, Bangladesh, and the Bay of Bengal). It appears that CH4 is an ideal monsoon tracer in the upper troposphere due to its extended lifetime and the strong South Asian emissions. Furthermore, we used the measurements and model results to study the dynamics of the AMA over several weeks during the monsoon season, with an emphasis on the southern and western areas in the upper troposphere. We distinguished four AMA modes based on different meteorological conditions. On one occasion we observed that under the influence of dwindling flow the transport barrier between the anticyclone and its surroundings weakened, expelling air masses from the AMA. The trace gases exhibited a distinct AMA fingerprint; we also found that CH4 accumulated over the course of the OMO campaign.

scholarly journals An algorithm for detecting <i>Trichodesmium</i> surface blooms in the South Western Tropical Pacific

2011 ◽  
Vol 8 (12) ◽  
pp. 3631-3647 ◽  
Author(s):  
C. Dupouy ◽  
D. Benielli-Gary ◽  
J. Neveux ◽  
Y. Dandonneau ◽  
T. K. Westberry
Keyword(s):  
Co2 Sequestration ◽  
New Caledonia ◽  
Tropical Pacific ◽  
The South ◽  
Western Tropical Pacific ◽  
Tropical Oceans ◽  
Fiji Islands ◽  
C And N ◽  
In Situ Observations

Abstract. Trichodesmium, a major colonial cyanobacterial nitrogen fixer, forms large blooms in NO3-depleted tropical oceans and enhances CO2 sequestration by the ocean due to its ability to fix dissolved dinitrogen. Thus, its importance in C and N cycles requires better estimates of its distribution at basin to global scales. However, existing algorithms to detect them from satellite have not yet been successful in the South Western Tropical Pacific (SP). Here, a novel algorithm (TRICHOdesmium SATellite) based on radiance anomaly spectra (RAS) observed in SeaWiFS imagery, is used to detect Trichodesmium during the austral summertime in the SP (5° S–25° S 160° E–170° W). Selected pixels are characterized by a restricted range of parameters quantifying RAS spectra (e.g. slope, intercept, curvature). The fraction of valid (non-cloudy) pixels identified as Trichodesmium surface blooms in the region is low (between 0.01 and 0.2 %), but is about 100 times higher than deduced from previous algorithms. At daily scales in the SP, this fraction represents a total ocean surface area varying from 16 to 48 km2 in Winter and from 200 to 1000 km2 in Summer (and at monthly scale, from 500 to 1000 km2 in Winter and from 3100 to 10 890 km2 in Summer with a maximum of 26 432 km2 in January 1999). The daily distribution of Trichodesmium surface accumulations in the SP detected by TRICHOSAT is presented for the period 1998–2010 which demonstrates that the number of selected pixels peaks in November–February each year, consistent with field observations. This approach was validated with in situ observations of Trichodesmium surface accumulations in the Melanesian archipelago around New Caledonia, Vanuatu and Fiji Islands for the same period.

On the role of tropical waves triggering extreme rainfall and flood in Sulawesi, Indonesia: a multi-scale interaction perspective

2020 ◽  
Author(s):  
Beata Latos ◽  
Thierry Lefort ◽  
Maria Flatau ◽  
Donaldi Permana ◽  
Piotr Flatau ◽  
...  
Keyword(s):  
Extreme Rainfall ◽  
Active Phase ◽  
Radar Data ◽  
Kelvin Wave ◽  
The South ◽  
Sea Surface Temperature Anomalies ◽  
Extreme Rain ◽  
In Situ Observations ◽  
Rain Events

&lt;p&gt;On January 22, 2019 extreme rainfall in the South-Western Sulawesi, Indonesia, triggered a massive, deadly flood, the most devastating one ever reported. This happened during an interaction of a robust Convectively Coupled Kelvin Wave (CCKW) and Equatorial Rossby Wave (ER). Potential causes of a flood include Madden Julian-Oscillation active phase, rainy season with monsoonal flow in the Karimata Strait, positive sea surface temperature anomalies supportive of convection, and synoptic-scale weather systems. All these factors can contribute to extreme rainfall and a flood development. Nonetheless, here we show that in this particular case enhancement of low-level westerlies led to convergence and forced ascend of moist air over orographic features of the south-western Sulawesi. This chain of processes was a result of a propagation of a CCKW, with contribution from an ER. Satellite and radar data analysis, as well as in-situ observations reveal that convergence and strong westerlies in the Java Sea, forced by the CCKW, resulted in the rain events in Jeneberang River Basin and the devastating flood in the city of Makassar.&lt;/p&gt;&lt;p&gt;Additional analysis of 20 years of the flood database together with in situ observations and satellite data support our hypothesis, based on this case study, of a significance of an enhanced westerlies as a precursor of extreme rain events and floods in Makassar, the capital and most populous city in Sulawesi.&lt;/p&gt;

scholarly journals Near-Inertial Waves Induced by Typhoon Megi (2010) in the South China Sea

2021 ◽  
Vol 9 (4) ◽  
pp. 440
Author(s):  
Anzhou Cao ◽  
Zheng Guo ◽  
Yunhe Pan ◽  
Jinbao Song ◽  
Hailun He ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Vertical Direction ◽  
The South China Sea ◽  
Inertial Waves ◽  
The South ◽  
China Sea ◽  
Synoptic Wind ◽  
In Situ Observations

Near-inertial waves (NIWs) are a kind of internal wave, which are usually generated by synoptic wind forcing and play an important role in the oceanic energy budget. However, the lack of in situ observations limits our understanding of NIWs to some extent. Through a comparison with in situ observations, in this study, we first showed that the hybrid coordinate ocean model reanalysis results could reasonably reproduce the typhoon-induced NIWs, and we then adopted these data to investigate the NIWs induced by typhoon Megi in 2010 in the South China Sea (SCS). The results indicate that Megi-induced near-inertial kinetic energy was mainly concentrated in the SCS Basin. In the vertical direction, Megi-induced NIWs could propagate to 1000 m depth. The damping and modal content of Megi-induced NIWs were site-dependent: In the region near Megi’s track, NIWs were dominated by the first three baroclinic modes and damped quickly; whereas in two zones to the west of the Luzon Island and Luzon Strait, the e-folding time of Megi-induced NIWs could be longer than 20 days and higher modes (mode-4 to mode-7) were enhanced several days after the passage of Megi. Possible mechanisms of these phenomena were also explored in this study.

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