Dust Storms and Long‐Range Transport of Dust by Kelvin Waves in East Asia

فرآیندهای جوّی خاص و برهمکنش آن ها با سطح زمین، عامل شکل گیری و تکامل یک توفان گردوغبار سنگین بشمار می آیند و در شناسایی مسیرهای انتقال توفان حائز اهمیت هستند. توزیع زمانی و مکانی غبار، در یک رخداد گردوغباری شدید در طول روزهای 4 تا 8 جولای 2009، با استفاده از شبیه سازی، به‌وسیله‌ مدل WRF/Chem ، مشاهدات ایستگاهی و تصاویر ماهواره ای مورد تجزیه‌وتحلیل قرارگرفته است. آنالیز وضعیت جوی شبیه‌سازی‌شده نشان داد، در صورتی بیشینه غلظت گردوغبار در تراز پایین اتفاق می افتد که در ناحیه منشأ غبار، گرادیان فشاری افقی قابل‌قبول با همرفت قوی در توده هوای مستقر در سامانه های چرخندی همراه باشد. در مورد انتخابی وضعیت جوی باعث ایجاد یک برش باد سطحی قوی روی مناطق انتشار غبار شناخته شده روی عراق شده بود. چرخند جبهه ای در مورد مطالعه شده، خاک را مجبور به فرسایش و باعث پراکنش و انتقال گردوغبار تا مسافت های بسیار حتی تا صدها کیلومتر کرده است. نتایج شبیه سازی نشان می داد که ذرات گردوغبار با شعاع کمتر از یک میکرومتر و با غلظت قابل‌ملاحظه، از رشته‌کوه‌های زاگرس عبور کرده و در 6 جولای 2009 ایران مرکزی و حتی کلان‌شهر تهران را تحت تأثیر قرار داده و دو روز بعد ایران را از جهت شمال شرق ترک کرده است. غلظت های شبیه‌سازی‌شده، اعتبار خوبی را از توزیع زمانی و مکانی غلظت گردوغبار با توجه به تصاویر مرئی ماهواره ای از سنجنده مودیس و گزارش های ساعتی دید افقی در شبکه ایستگاه های همدیدی نشان داده بود. با توجه به اعتبارسنجی های انجام‌شده، کارایی مدل برای شبیه سازی توزیع زمانی و مکانی توفان گردوغبار در طول منطقه تحت تأثیر در دوره شبیه سازی مورد تأیید قرار گرفت. مدل عددی WRF/Chem می تواند جهت پیش بینی شکل‌گیری و تکامل این پدیده عملیاتی شود.

A study of the dust emission, transport, and deposition is very important for understanding of the various health and social impacts on the local human population, biogeochemical cycle, and the global environmental change. The entry of dust into the atmosphere results from the occurrence of different scales of dust storms resulting from the multi-scale atmospheric processes ranging from the synoptic to near meso-scales of atmospheric motion. In this context, to find the causes of severe dust storms that occurred in the past over north-west Africa, central-north Africa, and Middle east we did a research work. In that study, significant roles of mountains (e.g., Atlas Mountains, Tibesti Mountains, and Sarwat Mountains) were found. For instances, there were a cross mountain flows that produced a leeside inversion layer, which facilitated for the imbalance of the exit region of the jet streak, prior to the large-scale dust storm; generation of terrain (i.e., mountains)-induced downslope winds in response to the transition of the atmospheric flow from a subcritical to supercritical state leading to dust storms; and generation of Kelvin waves supported by the mountains that were responsible for organizing the dust storms and wide distribution and transportation of dust away from the mountains. Regarding this, it is also hypothesized here that similar kinds of roles of mountains are also found in other geographical regions of the world, such as West/North/Northwest China and Mongolia where dust storms occur in the lee of the mountains, (i.e., Tien Shan/ Gobi Altai Mountains/ Khangai Mountains) and involve the long-range transport of atmospheric particulate matter originating from dryland areas. Such events are affecting large numbers of people and their environment especially in spring season because East Asia is the one of the most densely populated areas of the world. In this scenario, these kinds of studies will also be beneficial for analyses of roles of the synoptic features, and identification of their dynamical characteristics are important for evaluating different synoptic dust regimes and their development. So, for the current study, based on the severity of dust storms some cases of dust storms, which occurred in the lee of the respective mountains of China and Mongolia in the past, are considered.Keywords: Mountains, Dust Storms, Jet streak, Atmosphere

Dust storms which are considered as a cause of climatic and public health concerns are induced by natural and anthropogenic activities. In this paper, based on Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images, a new algorithm is developed to automatically detect dust storms over water body and land surfaces. The proposed method applies two different strategies for dust storm detection over water and land surfaces through the combination of various dust indices extracted from reflectance and thermal MODIS channels. It overcomes the disadvantages of previously developed algorithms taking into account the MODIS spectral band 7 (2105–2155 nm) to discriminate between dark and bright land surfaces. Different newly defined dust indices using proper thresholds are then employed for dust storm detection over two land surface classes as well as the water body. The proposed algorithm is applied to six dust-contaminated MODIS images covering southwestern Iran, northeastern Saudi Arabia, and southeastern Iraq. The results show that the proposed dust storm detection method performs well over areas covering features such as bright land surfaces and clouds whose spectral behavior is similar to that of the dust plumes. The results are compared to those obtained from two widely used previously developed dust storm detection algorithms. The comparison of the results with those achieved from visual inspections demonstrates that the proposed method detects the dust storm with the accuracy of ~ 95%, whereas the other two methods result in the dust detection accuracies of ~ 69% and ~ 68%. Furthermore, the proposed approach is found to be promising for dust storm detection over the study area.

There is still ambiguity in distinguishing dust storms from clouds in cloudy weather satellite images. This research addresses this challenge by developing and applying a new technique for detecting dust storms in cloudy weather over Iraq using the unique capabilities of the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. Specifically, this study will focus on the thermal infrared bands of MODIS, particularly bands 29 (8.55 μm), 31 (11.03 μm), and 32 (12.02 μm) to detect dust events and isolate them from clouds. These bands are crucial because dust particles interact with thermal radiation differently than cloud particles and the Earth’s surface. By analyzing the brightness temperature difference (BTD) between these specific thermal infrared bands, it is possible to identify the distinct spectral signature of dust even when clouds obscure visible channels. Four specific dust events have been selected over Iraq on May 4th and 5th, 2025, to test this approach. For each day, we utilized daytime imagery from the Terra satellite and nighttime imagery from the Aqua satellite. We then processed the raw MODIS data from bands 29, 31, and 32 to generate RGB dust storm composite images. These RGB dust storm composites perfectly matched the forecasts and observations provided by well-established dust storm forecasting websites, strongly validating the effectiveness of our technique, and gave good results in isolating dust storms even in clouds presence, which was the primary goal of this research.

The effect of turbulent motions on the transport of dust and heat in the development stage of dust storms induced by cold front

Dust storms are strongly and negatively associated with the annual cycle of rainfall and coincide with the west and southwesterly winds in west and south west of Iran. Accuracy assessment of particulate matter products of moderate resolution image spectroradiometer was studied in this research. Moderate resolution image spectroradiometer products consist of aerosol optical thickness, its corresponding image red, green and blue and moderate resolution image spectroradiometer/ terra calibrated radiances 5 minutes L1B swath 1 km, which shows the environmental information at terrestrial, atmospheric and ocean phenomenology. Daily aerosol optical thickness data retrieved from moderate resolution image spectroradiometer from May 2009 to May 2010 were compared with the amount of particulate matter measured at ground in Sanandaj, Iran, using non-linear correlation coefficient. Results showed that the moderate resolution image spectroradiometer image / terra calibrated radiances 5 minutes L1B swath 1 km is able to detect dust storms distribution and their blowing direction over study area clearly. The air quality conditions obtained in with dust storm period were unhealthy and correlation coefficients between moderate resolution image spectroradiometer aerosol optical thickness and particulate matter concentration in this period were higher than without dust storm period. The moderate resolution image spectroradiometer aerosol optical thickness values lower than 0.1 were acquired uncertainty level. Comparison of moderate resolution image spectroradiometer images/ terra calibrated radiances 5 minutes L1B swath 1 km and image red, green and blue showed that moderate resolution image spectroradiometer has limitation in retrieval of aerosol optical thickness from the dust storm with high concentration of particulate matter. This study reveals that the algorithm which is applied to refine the aerosol optical thickness is not able to recognize the amount of particulate matter in low and very high concentrations sensitively. No study has previously been conducted to investigate the accuracy of the moderate resolution image spectroradiometer particulate matter products.

Meteorological observations, in situ data, and satellite images of dust episodes were used already in the 1970s to estimate that 100 Tg of dust are transported from Africa over the Atlantic Ocean every year between June and August and are deposited in the Atlantic Ocean and the Americas. Desert dust is a main source of nutrients to oceanic biota and the Amazon forest, but it deteriorates air quality, as shown for Florida. Dust affects the Earth radiation budget, thus participating in climate change and feedback mechanisms. There is an urgent need for new tools for quantitative evaluation of the dust distribution, transport, and deposition. The Terra spacecraft, launched at the dawn of the last millennium, provides the first systematic well‐calibrated multispectral measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument for daily global analysis of aerosol. MODIS data are used here to distinguish dust from smoke and maritime aerosols and to evaluate the African dust column concentration, transport, and deposition. We found that 240 ± 80 Tg of dust are transported annually from Africa to the Atlantic Ocean, 140 ± 40 Tg are deposited in the Atlantic Ocean, 50 Tg fertilize the Amazon Basin (four times as previous estimates, thus explaining a paradox regarding the source of nutrition to the Amazon forest), 50 Tg reach the Caribbean, and 20 Tg return to Africa and Europe. The results are compared favorably with dust transport models for maximum particle diameter between 6 and 12 μm. This study is a first example of quantitative use of MODIS aerosol for a geophysical research.

Abstract. The Taklamakan Desert (TD) is a major source of mineral dust emissions into the atmosphere. These dust particles have the ability to darken the surface of snow on the surrounding high mountains after deposition, significantly impacting the regional radiation balance. However, previous field measurements have been unable to capture the effects of severe dust storms accurately, and their representation on regional scales has been inadequate. In this study, we propose a modified remote-sensing approach that combines data from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite and simulations from the Snow, Ice, and Aerosol Radiative (SNICAR) model. This approach allows us to detect and analyze the substantial snow darkening resulting from dust storm deposition. We focus on three typical dust events originating from the Taklamakan Desert and observe significant snow darkening over an area of ∼ 2160, ∼ 610, and ∼ 640 km2 in the Tien Shan, Kunlun, and Qilian mountains, respectively. Our findings reveal that the impact of dust storms extends beyond the local high mountains, reaching mountains located approximately 1000 km away from the source. Furthermore, we observe that dust storms not only darken the snowpack during the spring but also in the summer and autumn seasons, leading to increased absorption of solar radiation. Specifically, the snow albedo reduction (radiative forcing) triggered by severe dust deposition is up to 0.028–0.079 (11–31.5 W m−2), 0.088–0.136 (31–49 W m−2), and 0.092–0.153 (22–38 W m−2) across the Tien Shan, Kunlun, and Qilian mountains, respectively. This further contributes to the aging of the snow, as evidenced by the growth of snow grain size. Comparatively, the impact of persistent but relatively slow dust deposition over several months during non-event periods is significantly lower than that of individual dust events. This highlights the necessity of giving more attention to the influence of extreme events on the regional radiation balance. This study provides a deeper understanding of how a single dust event can affect the extensive snowpack and demonstrates the potential of employing satellite remote sensing to monitor large-scale snow darkening.

ABSTRACTThe impacts of wind-blown desert sand and dust are a major concern of environmental and climate study due to their global extent. This article investigates the sand and dust storms detection in Saudi Arabia using Moderate Resolution Imaging Spectroradiometer (MODIS) data, both from Terra and Aqua satellite systems for the years 2002–2011. Normalized Difference Dust Index (NDDI) is applied for the detection of sand and dust storms whilst MODIS band 31 is applied to discriminate atmospheric sand and dust from that present on the ground. In addition, the data from Meteosat satellite, AERONET station, and meteorological stations are used to validate NDDI-based sand and dust storm events. The results of the study show that NDDI can successfully identify and differentiate sand and dust storms from clouds whilst MODIS band 31 can discriminate aerial and surface sand and dust over Saudi Arabia. The results also show that the multi-source data, that is MODIS, Meteosat, AERONET, and meteorological stations, can be very valuable for tracking sand and dust storm events. As no such attempt in the past has been made in Saudi Arabia, it is envisaged that the results of this study will be helpful in planning remote-sensing data for the climate change study in the region.

Retrieval of Leaf Area Index in mountain grasslands in the Alps from MODIS satellite imagery

The dust storm is one of the severe natural disasters that has been recently threatening the Middle East region due to climate changes and human activities. This phenomenon has become a national crisis in some countries in this region in previous years, especially in spring and summer. This research aims to detect and monitor the areas covered by the seasonal and occasional dust storm from (Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. MODIS imagery possesses impressive spectral and temporal characteristics that are essential for such an environmental application of Earth observations. An efficient algorithm, based on the spectral and statistical analysis of both thermal and reflectance bands of MODIS data, was developed through a decision tree method. To this end, an index was proposed to detect the dust over the land using the brightness temperature of thermal bands. The results of the proposed algorithm were assessed utilizing ground-based observation of synoptic stations. The proposed method showed high reliability and performance as well as the automatic capability of dust detection in land and sea areas of the image simultaneously. The evaluation of results showed that the proposed algorithm could detect thin and thick dust storms with an overall accuracy of about 80%. Moreover, the dust monitoring results visually agreed well with the Ozone Monitoring Instrument aerosol index dust products.

Abstract. Based on the large-scale transport of dust driven by the winds parallel to the mountains in the Harmattan, Saudi Arabian, and Bodélé Depression dust storm cases, a detailed study of the generation of Kelvin waves and its possible role in organizing these dust storms and large-scale dust transport was accomplished. For this study, observational and numerical model analyses were done in an in depth manner. For this, MERRA reanalysis data sets; WRF-simulated high-resolution variables; MODIS Aqua and Terra images; EUMETSAT images; NAAPS aerosol modeling plots; and MERRA-2 dust scattering aerosol optical depth (AOD) modeling plots, surface observations, and rawinsonde soundings were analyzed for each of these three case studies. We found that there were meso-β-scale (horizontal length scale of 20–200 km) adjustment processes resulting in Kelvin waves only in the Harmattan and the Bodélé Depression cases. The Kelvin wave preceded a cold pool accompanying the air behind the large-scale cold front instrumental in the major dust storm. We find that this Kelvin wave organized the major dust storm in a narrow zone parallel to the mountains before it expanded upscale (meso-α to synoptic).

We examine the complex meteorological processes involved in the development of multiple dust storms in the middle of March 2022 over North Africa by means of multi-level high-resolution reanalysis datasets, and satellite and surface observations. These dust storms ultimately transported a remarkable amount of dust into Europe, and in particular to the Iberian Peninsula.The analyses show that baroclinic Rossby Wave Breaking (RWB) events over two regions: the eastern North Atlantic and the western Eurasian border, resulted in the creation of a downscale confluence of low-level jets that ablated dust in the Sahara Desert. One of these active baroclinic regions involved multiple wave-breaks over western Russia and the Middle East that transported unseasonably cold air southwestward into Egypt and Sudan. A second active baroclinic region occurred along the North African Atlantic Coast where rapid downstream dispersion of energy was focused in response to very intense cyclogenesis over Labrador. The cold pool which propagated into northwestern Africa and cold air over northeastern Africa effectively sandwiched hot Saharan air in between the Hoggar and Atlas Mountain Ranges. The fronts separating these air masses became juxtaposed with the two mountain ranges creating ideal conditions for blocking and multiple barrier jets’ genesis. These barrier jets each combined with larger scale semi-geostrophic low-level jet formation, resulted in the ablation of dust into two separate large plumes both of which were transported poleward out of North Africa into Europe around a upper-level cutoff-low near Iberia slowly displacing downstream.The blocked RWB forcing the penetration of cold air over eastern Africa constitutes a substantial difference with respect to other more frequent events where RW trains intensify, penetrate equatorward into North Africa and propagate eastward.Work funded by MCIN/AEI/ 10.13039/501100011033 under Grant PID2020-115153RB-I00 (rROSSETA Project).

Geologic and geophysical mapping has been so far limited to the traditional single-method GIS-based mapping. A new approach combining integrated analysis of data on geology, gravity, topography and geomorphology is presented for regional characterization of the geophysical setting in Mongolia: the Gobi Altai Mountains, the Khangai Mountains and Khentii Mountains with surrounding areas. Nine new maps have been produced from the high-resolution datasets: GEBCO, gravity raster, USGS geological data and SRTM-90 DEM geomorphological grid. Methodology includes three tools for cartographic data visualization: i) Generic Mapping Tools (GMT), ii) R programming language (‘raster’ and ‘tmap’ libraries); iii) QGIS. The results demonstrated strong agreement between the estimated values in gravity and topography grids, distribution of geological units and provinces over the country and geomorphological landforms with respect to the mountain ranges: Altai, Khangai and Khentii Mountains. The highest values in the gravity anomalies correspond to the mountain ranges in the Altai Mountains and Khangai Mountains (<80 mGal); high values correspond to the Khentii Mountains (20–60 mGal). Contrariwise, the basins of the Uvs Nuur and Khyargas Nuur show negative values (<-80 mGal). The NE- to NNE-oriented faulting and rift basins are clearly visible in the geophysical grids and geologic maps. The geomorphometric analysis performed based on the SRTM-90 DEM using R scripting demonstrated (1) slope, (2) aspect, (3) hillshade and (4) elevation models of Mongolia supported by histograms of data distribution and frequency. The study contributed to the cartographic methods and regional geological studies of Mongolia.

By the numerical experiments, we clarify the regional wind systems that generate dust storms in the Tarim basin, Northwest China. In the basin, dust storms are generated by a mesoscale cold wind system induced by a synoptic‐scale cold air mass behind a cold front. The intruding course of the mesoscale cold wind into the basin can be classified into three patterns. The first pattern is characterized by the easterly mesoscale cold wind, which is separated from the synoptic‐scale cold westerly and turns westward after going around the eastern side of the TianShan Mountains. The mesoscale cold wind categorized in the second pattern directly crosses over the TianShan Mountains, which often gives a very strong wind in the basin with the largest dust storms in the three patterns. The third pattern indicates that the cold wind crosses over Pamir plateau, although the magnitude of the dust storm is usually small.