Modelling the 2021 East Asia super dust storm using FLEXPART and FLEXDUST and its comparison with reanalyses and observations

The 2021 East Asia sandstorm began from the Eastern Gobi desert steppe in Mongolia on March 14, and later spread to northern China and the Korean Peninsula. It was the biggest sandstorm to hit China in a decade, causing severe air pollution and a significant threat to human health. Capturing and predicting such extreme events is critical for society. The Lagrangian particle dispersion model FLEXPART and the associated dust emission model FLEXDUST have been recently developed and applied to simulate global dust cycles. However, how well the model captures Asian dust storm events remains to be explored. In this study, we applied FLEXPART to simulate the recent 2021 East Asia sandstorm, and evaluated its performance comparing with observation and observation-constrained reanalysis datasets, such as the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) and CAMS global atmospheric composition forecasts (CAMS-F). We found that the default setting of FLEXDUST substantially underestimates the strength of dust emission and FLEXPART modelled dust concentration in this storm compared to that in MERRA-2 and CAMS-F. An improvement of the parametrization of bare soil fraction, topographical scaling, threshold friction velocity and vertical dust flux scheme based on Kok et al. (Atmospheric Chemistry and Physics, 2014, 14, 13023-13041) in FLEXDUST can reproduce the strength and spatio-temporal pattern of the dust storm comparable to MERRA-2 and CAMS-F. However, it still underestimates the observed spike of dust concentration during the dust storm event over northern China, and requires further improvement in the future. The improved FLEXDUST and FLEXPART perform better than MERRA-2 and CAMS-F in capturing the observed particle size distribution of dust aerosols, highlighting the importance of using more dust size bins and size-dependent parameterization for dust emission, and dry and wet deposition schemes for modelling the Asian dust cycle and its climatic feedbacks.Peer reviewe

Evaporative implications of dry-air outbreaks over the northern Red Sea.

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Atmospheres, 124(9), (2019): CP3-4861, doi: 10.1029/2018JD028853.We investigate the impacts of westward wind events on the Red Sea evaporation using the 35‐year second Modern‐Era Retrospective analysis for Research and Applications reanalysis and a 2‐year‐long record of in situ observations from a heavily instrumented air‐sea interaction mooring. These events are common during boreal winter, and their effects are similar to cold‐air outbreaks that occur in midpolar and subpolar latitudes. They cause extreme heat loss from the sea, which is dominated by latent heat fluxes. Different from cold‐air outbreaks, the intensified heat loss is due to the low relative humidity as we show through latent heat flux decomposition. Rainfall is negligible during these events, and we refer to them as dry‐air outbreaks. We also investigate the general atmospheric circulation pattern that favors their occurrence, which is associated with an intensified Arabian High at the north‐central portion of the Arabian Peninsula—a feature that seems to be an extension of the Siberian High. The analyses reveal that the westward winds over the northern Red Sea and the winter Shamal winds in the Persian Gulf are very likely to be part of the same subsynoptic‐scale feature. The second Modern‐Era Retrospective analysis for Research and Applications reanalysis indicates that the occurrence of westward wind events over the northern Red Sea has grown from 1980 to 2015, especially the frequency of large‐scale events, the cause of which is to be investigated. We hypothesize that dry‐air outbreaks may induce surface water mass transformation in the surface Red Sea Eastern Boundary Current and could represent a significant process for the oceanic thermohaline‐driven overturning circulation.We thank the three anonymous reviewers and the associated editor who provided valuable comments that contributed to the improvement of the present paper. We wish to acknowledge the use of the Ferret program (NOAA/PMEL) and NCL (doi: 10.5065/D6WD3XH5) for analysis and graphics in this paper. We thanks Julie Hildebrandt for helping with the final manuscript version, Marcio Vianna for fruitful discussion about this work, and Stephen Swift for pointing out the long time series from Yenbo and Wejh at the National Climatic Data Center (NCDC/NOAA). We acknowledge the Global Modeling and Assimilation Office (GMAO) and the Goddard Earth Sciences Data and Information Services Center (GESDISC) for the dissemination of MERRA‐2 reanalysis and the NCDC/NOAA for making the Global Surface Summary of the Day freely and easily available on the internet. MERRA‐2 and QuikSCAT winds at 25 and 12.5 km data are available online (https://disc.gsfc.nasa.gov/datareleases/merra_2_data_release; www.remss.com/missions/qscat/; and https://podaac.jpl.nasa.gov, respectively). The in situ data from the WHOI/KAUST mooring is available at a WHOI repository (http://uop.whoi.edu/projects/kaust/form.php) and provided solely for academic and research purposes. The mooring data collected during the WHOI‐KAUST collaboration was made possible by award USA00001, USA00002, and KSA00011 to the WHOI by the KAUST in the Kingdom of Saudi Arabia. This work was supported by NSF grant OCE‐1435665 and NASA grant NNX14AM71G.2019-10-0

Comprehensive analysis of thermodynamics,dynamics and associated variability

During summertime Saharan heat low, a region of low pressure system, is formed as a result of large solar insolation superimposed with the convergence of west African South westerly monsoon flow and dry north easterly Harmattan flow along the intertropical discontinuity. This region plays significant role in the initiation and development of the West African Monsoon. The Saharan heat low is co-located with region of maximum load of dust aerosol which is known to have impact on the climate. Further the Saharan heat low plays key role in the global circulations including its role in formation of African Easterly Jets and African Easterly Waves. Despite its role in influencing the dynamic and thermodynamics of the region, the Saharan Heat low is not extensively studied partly due to lack of comprehensive data due to the harsh weather conditions of the region. Climate system of the Saharan heat low is a result of different complicated atmospheric and land surface processes most dominantly immense solar input at the surface, large convergence of sensible heat flux from the ground into the atmosphere, and low level cooling by horizontal advection of moisture from the surrounding area. These dynamical and thermodynamical processes take part in transport and redistribution of heat and transport of the moisture in the region. This thesis aims at providing a detailed analysis of the physical processes responsible for the development, maintenance, and decadal variability of the Saharan heat low region. I investigate three specific aspects of the Saharan heat low region. 1. Heat and Moisture Budget: Heat and moisture are drivers of dynamics and thermodynamics of a region. Previous studies presented heat and moisture budget of the Saharan heat Low without attributing to the detailed mechanisms by which heat and moisture is transported from the surrounding area to the Sahara heat low and vice versa. This thesis presents components of heat and moisture budget resulting from mean and transient flows that are responsible for heating/cooling and moistening/drying of the Sahara heat low region. Heat and moisture budget are derived using commonly used reanalyses simulations (ERA-I, NCEP, and MERRA) and comparison of the results between the three reanalyses are made. I investigate the mechanisms responsible for the decadal variability of intensity of the Sahara heat low and provide implications. This work has not been done previously to the best of knowledge. 2. Role of Dust and Water vapor in controlling the radiative flux: Recent studies show that water vapour greenhouse forcing is responsible for intensification of the Saharan heat low and as a consequence recovery of Sahel rainfall. Dust aerosol is known to have impact on the climate through its interaction with radiation. The large dust load in the Sahara heat low makes it important in controlling the variability in the radiative budget of the region. Previous studies have quantified the role of dust and water vapour in the region in controlling day to day variability in the radiative flux in the heat low. There is still uncertainty in the radiative forcing and associated variability partly due to lack of observational data. Furthermore separating the radiative effect of dust from that of water vapour is challenging due to the co-variability of dust and water vapour. This thesis quantifies separate and combined effect of dust and water vapour in controlling the radiative flux of the Saharan heat low using the recently made FENNEC observations of meteorological variables and dust loading. Theoretical experiments are made to study sensitivity of radiative flux to variations in dust and water vapour. 3. Characteristics of convective density currents: Convective down drafting density currents (cold pools) are ubiquitous features of the Saharan Heat low region which are shown to play important role in the transport of moisture and emission of dust in the region. Despite this, the characteristics of these atmospheric processes are not well studied in the Sahara Heat Low. Improving our knowledge of properties of convective density currents is imperative to better understand atmospheric processes within boundary layer of the Saharan heat low and thus improve model simulation performance. Here I provide magnitude, spatial distribution, and seasonal variability of cold pools using data from the Automatic weather Station (AWS) spread over the Sahara desert. I implement a unique identification method which is further verified by satellite observations of cold pool signatures. Once cold pools are identified at all stations, statistical description of the occurrence frequency and distribution are presented. Finally I asses reanalyses model simulation of convection triggered cold pool outflows through comparison with measurements

State of the climate in 2018

In 2018, the dominant greenhouse gases released into Earth’s atmosphere—carbon dioxide, methane, and nitrous oxide—continued their increase. The annual global average carbon dioxide concentration at Earth’s surface was 407.4 ± 0.1 ppm, the highest in the modern instrumental record and in ice core records dating back 800 000 years. Combined, greenhouse gases and several halogenated gases contribute just over 3 W m−2 to radiative forcing and represent a nearly 43% increase since 1990. Carbon dioxide is responsible for about 65% of this radiative forcing. With a weak La Niña in early 2018 transitioning to a weak El Niño by the year’s end, the global surface (land and ocean) temperature was the fourth highest on record, with only 2015 through 2017 being warmer. Several European countries reported record high annual temperatures. There were also more high, and fewer low, temperature extremes than in nearly all of the 68-year extremes record. Madagascar recorded a record daily temperature of 40.5°C in Morondava in March, while South Korea set its record high of 41.0°C in August in Hongcheon. Nawabshah, Pakistan, recorded its highest temperature of 50.2°C, which may be a new daily world record for April. Globally, the annual lower troposphere temperature was third to seventh highest, depending on the dataset analyzed. The lower stratospheric temperature was approximately fifth lowest. The 2018 Arctic land surface temperature was 1.2°C above the 1981–2010 average, tying for third highest in the 118-year record, following 2016 and 2017. June’s Arctic snow cover extent was almost half of what it was 35 years ago. Across Greenland, however, regional summer temperatures were generally below or near average. Additionally, a satellite survey of 47 glaciers in Greenland indicated a net increase in area for the first time since records began in 1999. Increasing permafrost temperatures were reported at most observation sites in the Arctic, with the overall increase of 0.1°–0.2°C between 2017 and 2018 being comparable to the highest rate of warming ever observed in the region. On 17 March, Arctic sea ice extent marked the second smallest annual maximum in the 38-year record, larger than only 2017. The minimum extent in 2018 was reached on 19 September and again on 23 September, tying 2008 and 2010 for the sixth lowest extent on record. The 23 September date tied 1997 as the latest sea ice minimum date on record. First-year ice now dominates the ice cover, comprising 77% of the March 2018 ice pack compared to 55% during the 1980s. Because thinner, younger ice is more vulnerable to melting out in summer, this shift in sea ice age has contributed to the decreasing trend in minimum ice extent. Regionally, Bering Sea ice extent was at record lows for almost the entire 2017/18 ice season. For the Antarctic continent as a whole, 2018 was warmer than average. On the highest points of the Antarctic Plateau, the automatic weather station Relay (74°S) broke or tied six monthly temperature records throughout the year, with August breaking its record by nearly 8°C. However, cool conditions in the western Bellingshausen Sea and Amundsen Sea sector contributed to a low melt season overall for 2017/18. High SSTs contributed to low summer sea ice extent in the Ross and Weddell Seas in 2018, underpinning the second lowest Antarctic summer minimum sea ice extent on record. Despite conducive conditions for its formation, the ozone hole at its maximum extent in September was near the 2000–18 mean, likely due to an ongoing slow decline in stratospheric chlorine monoxide concentration. Across the oceans, globally averaged SST decreased slightly since the record El Niño year of 2016 but was still far above the climatological mean. On average, SST is increasing at a rate of 0.10° ± 0.01°C decade−1 since 1950. The warming appeared largest in the tropical Indian Ocean and smallest in the North Pacific. The deeper ocean continues to warm year after year. For the seventh consecutive year, global annual mean sea level became the highest in the 26-year record, rising to 81 mm above the 1993 average. As anticipated in a warming climate, the hydrological cycle over the ocean is accelerating: dry regions are becoming drier and wet regions rainier. Closer to the equator, 95 named tropical storms were observed during 2018, well above the 1981–2010 average of 82. Eleven tropical cyclones reached Saffir–Simpson scale Category 5 intensity. North Atlantic Major Hurricane Michael’s landfall intensity of 140 kt was the fourth strongest for any continental U.S. hurricane landfall in the 168-year record. Michael caused more than 30 fatalities and $25 billion (U.S. dollars) in damages. In the western North Pacific, Super Typhoon Mangkhut led to 160 fatalities and$6 billion (U.S. dollars) in damages across the Philippines, Hong Kong, Macau, mainland China, Guam, and the Northern Mariana Islands. Tropical Storm Son-Tinh was responsible for 170 fatalities in Vietnam and Laos. Nearly all the islands of Micronesia experienced at least moderate impacts from various tropical cyclones. Across land, many areas around the globe received copious precipitation, notable at different time scales. Rodrigues and Réunion Island near southern Africa each reported their third wettest year on record. In Hawaii, 1262 mm precipitation at Waipā Gardens (Kauai) on 14–15 April set a new U.S. record for 24-h precipitation. In Brazil, the city of Belo Horizonte received nearly 75 mm of rain in just 20 minutes, nearly half its monthly average. Globally, fire activity during 2018 was the lowest since the start of the record in 1997, with a combined burned area of about 500 million hectares. This reinforced the long-term downward trend in fire emissions driven by changes in land use in frequently burning savannas. However, wildfires burned 3.5 million hectares across the United States, well above the 2000–10 average of 2.7 million hectares. Combined, U.S. wildfire damages for the 2017 and 2018 wildfire seasons exceeded $40 billion (U.S. dollars)

Evaluation of the transport and chemistry of climate-relevant species in the lower stratosphere

This thesis investigates aspects of the chemistry and transport of the upper troposphere and lower stratosphere (UTLS), with a particular focus on the Asian Summer Monsoon (ASM). The overall aims have been pursued through simulations of the TOMCAT three-dimensional (3-D) chemical transport model in comparison with aircraft, balloon and satellite observations. Scientific motivation for this work has been provided by the EU StratoClim project which conducted flight campaigns in Greece (2016) and Nepal (2017). Simulations of the transport of chemically active tracers to the UT depend critically on the treatment of convection. In this work I have tested and further developed an improvement to the existing TOMCAT model by using a convection scheme based on mass fluxes from archived meteorological analyses. This leads to more rapid uplift of chemical tracers, which is most apparent for those with short lifetimes (e.g. around 5 days). Both the old and new convection schemes have been evaluated against observations. The model has then been used to quantify the transport associated with the Asian Summer Monsoon (ASM) circulation, focusing on the interannual variability using decadal simulations forced by ERA-Interim reanalysis. The role of large-scale ascent versus convective transport has been investigated, along with the link between the interannual variability of the transport of surface-emitted CO to the UT to the strength of the ASM. Model intercomparisons of tropospheric age-of-air when the old (Tiedtke) convection scheme is applied, shows weak transport, in particular at UTLS levels, when compared with other state-of-the-art 3-D models. In contrast the new (archived mass flux) scheme shows faster and stronger transport reflected in a younger age-of-air in the UT. A multidecadal (1989-2017) simulation with idealized tracers show that the alternative convection schemes vastly impact the related confinement of such tracers in the ASM anticyclonic structure at 100 hPa. However, connecting this confinement with common metrics of the dynamical strength of the ASM circulation is not straightforward and does not lead to conclusive results over the time period modelled. The main chemical observations so far available from the StratoClim campaign are water vapour and CO. Comparison between the in-situ water data from the StratoClim and the ERA-Interim values confirms a negative bias in UTLS in the reanalyses over the Indian Subcontinent region. A full chemistry model simulation is able to capture the observed magnitude and variability of the observed CO well. Analysis of daily model output reveals an interesting tri-modal pattern of elevated CO in the ASM region, which is strongly dependent on convection over the Tibetan Plateau but not entirely due to it. Injection of brominated species into the stratosphere has been investigated using observations from the more extensive American 2013/14 Airborne Tropical Tropopause Experiment (ATTREX) aircraft campaign in the Eastern Pacific. The model simulations with the new convective scheme agree well with UTLS observations of CHBr3, CH3Br, CH2Br2 and H-1211, confirming the injection of around 6 ppt bromine derived from very short-lived substances (VSLS) into the stratosphere. However, comparisons of observed and modeled BrO shows that this cannot account in all cases for the amount of inorganic bromine observed in the lower stratosphere, suggesting direct injection of significant levels (a few ppt) of inorganic bromine into the stratosphere in the Tropics. Finally, I have investigated the impact of artificial injection of particles into the stratosphere – so-called geoengineering through solar radiation management to counteract climate change. I have assessed the possible impact of the underexplored particulate mineral substance, TiO2, on stratospheric ozone through enhanced heterogeneous chemistry. Model simulations, based on loadings causing a similar climate impact to the Mt Pinatubo eruption, show the injection of TiO2 particles in the stratosphere likely has only a small impact on present-day ozone concentrations (decrease of up to 0.06%). With further assumptions about the possible role of TiO2 on chlorine heterogeneous chemistry, a model simulation to 2049 with recurrent large Pinatubo-like volcanic eruptions shows that the impact with declining stratospheric chlorine loading is not more than a -2.5% change in ozone

CIRA annual report FY 2017/2018

Reporting period April 1, 2017-March 31, 2018

A modelling perspective on precipitationin the Indus River Basin: from synopticto Holocene variability

The Indus River civilisation was the first urban society in South Asia. Its demise, ca. 4000 years ago, might have been caused by environmental factors, such as recurrent drought conditions. Yet, palaeoclimate archives present a fragmented picture of the climate at that time. This thesis explores the potential value of global climate models to further interpret the archaeological context. Precipitation variability is investigated at various timescales due to their different impact on human societies and their importance in the climate system: the synoptic scale, the seasonal cycle, the inter-annual to multi-decadal variability, and the multi-millennial Holocene trends. The precipitation from several climate model simulations is evaluated at each of these timescales. Indus River Basin precipitation is first explored in observational datasets. This study highlights the quality of ERA5 reanalysis, which is used as a reference in the subsequent chapters. Statistical tools show that more than 80\% of the precipitation in the Upper Indus Basin is related to cross-barrier moisture transport along the Himalayan foothills. The climate models analysed (IPSL-CM6-A, MRI-ESM2-0 and GISS-E2-1-G) generally reproduce this process well, but the seasonality of cross-barrier moisture transport is biased, resulting in precipitation biases: the main wet season, the summer monsoon, is shorter and significantly dryer, while the second wet season, in winter, is longer and more active. The link between winter precipitation, cross-barrier moisture transport and Western Disturbances is further explored, first in ERA5 and then compared to IPSL-CM6-A model output. Sub-daily resolution is needed to determine the origin of the positive precipitation bias in winter. This bias is related to differences in the atmospheric circulation associated with Western Disturbances. The stronger Subtropical Westerly Jet is also key to understand the precipitation overestimation. Centennial to millennial-scale precipitation variability is more difficult to evaluate due to the short length of observations and the paucity of climate records, but the results suggest that inter-annual variability in the IPSL climate model family is overly dominated by atmosphere-only processes, with a potentially large impact of the precipitation response to external forcings. In addition to biases in the representation of mean precipitation and synoptic to inter-annual variability, climate models are also limited by the representation of other internal processes such as ocean circulation, and vegetation-dust aerosols, as well as by the uncertainty in some external forcings such as volcanic eruptions and the solar activity. Hence, at the present state, past-climate simulations do not provide the nuanced information of precipitation changes and variability that is needed to understand impact of precipitation variability on archaeological contexts, and will not do so until significant breakthroughs are achieved. Nevertheless, climate models remain a powerful tool for climatologists to investigate large-scale processes that can eventually better characterise climate variability.This research was carried out as part of the TwoRains project, which is supported by funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant 648609)

The Southern Ocean Observing System (SOOS)

[in “State of the Climate in 2014” : Special Supplement to the Bulletin of the American Meteorological Society Vol. 96, No. 7, July 2015

Atmospheric Research 2018 Technical Highlights

Atmospheric research in the Earth Sciences Division (610) consists of research and technology development programs dedicated to advancing knowledge and understanding of the atmosphere and its interaction with the climate of Earth. The Divisions goals are to improve understanding of the dynamics and physical properties of precipitation, clouds, and aerosols; atmospheric chemistry, including the role of natural and anthropogenic trace species on the ozone balance in the stratosphere and the troposphere; and radiative properties of Earths atmosphere and the influence of solar variability on the Earths climate. Major research activities are carried out in the Mesoscale Atmospheric Processes Laboratory, the Climate and Radiation Laboratory, the Atmospheric Chemistry and Dynamics Laboratory, and the Wallops Field Support Office. The overall scope of the research covers an end-to-end process, starting with the identification of scientific problems, leading to observation requirements for remote sensing platforms, technology and retrieval algorithm development; followed by flight projects and satellite missions; and eventually, resulting in data processing, analyses of measurements, and dissemination from flight projects and missions