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The United Arab Emirates holds great historical importance, as evidenced by many archaeological sites, such as the Jebel Hafit Tombs and the Hili Archeological Park in Al Ain. At the western edge of Mutaredh Oasis, a major new archaeological site was discovered in 2023 during a construction project. Several important archeological features have been documented, including an earthen mosque and boundary walls, Iron Age irrigation systems, and a circular stone tomb dating to the Bronze Age. However, the eastern edge of the Mutaredh site has remained unexplored to date. Ground Penetrating Radar (GPR) has been proven to be a successful method in mapping archaeological remains. Accordingly, a high-resolution GPR survey was carried out to identify the continuity of the unearthed archeological elements and delineate new unexplored features. A comprehensive 3D model of buried archaeological features was constructed using the acquired high-resolution GPR data in the eastern part of the Mutaredh site. Several selected anomalies have been observed, similar to the uncovered features in the western part of the Mutaredh site and structures documented in other nearby archaeological sites. The geometry and extension of these anomalies have enabled the possible identification of a further two Bronze Age circular tombs, as well as the delineation of a system of water channels (falaj), and irrigation networks with tree pits from the Iron Age. Moreover, walls probably belonging to the Late Islamic Age are identified. These findings suggest that Mutaredh has been a site of intensive human activity from the Bronze Age through to the Late Islamic period. Given the density of identified anomalies, further significant features are anticipated to lie buried in the immediate surrounding areas, promising continued insights into the area's rich archaeological heritage. The findings of this study may guide archaeologists to specific locations and assist in selecting the most appropriate excavation techniques for the verification stage. [ABSTRACT FROM AUTHOR]

The Arabian Peninsula (AP) is notable for its unique meteorological and climatic patterns and plays a pivotal role in understanding regional climate dynamics and dust emissions. The scarcity of ground-based observations makes atmospheric data essential, rendering reanalysis and satellite products invaluable for understanding weather patterns and climate variability. However, the accuracy of these products in the AP's desert environment has not been extensively evaluated. This study undertakes the first comprehensive validation of reanalysis products—the European Centre for Medium-Range Weather Forecasts' European Reanalysis version 5 (ERA5) and ERA5 Land (ERA5L), along with Clouds and Earth's Radiant Energy System (CERES) radiation fluxes—against measurements from the Liwa desert in the UAE. The data, collected during the Wind-blown Sand Experiment (WISE)–UAE field experiment from July 2022 to December 2023, includes air temperature and relative humidity at 2 m, 10 m wind speed, surface pressure, skin temperature, and net radiation fluxes. Our analysis reveals a strong agreement between ERA5/ERA5L and the observed diurnal T2m cycle, despite a warm night bias and cold day bias with a magnitude within 2 K. The wind speed analysis uncovered a bimodal distribution attributed to sea-breeze circulation and the nocturnal low-level jet, with the reanalysis overestimating the nighttime wind speeds by 2 m s−1. This is linked to biases in nighttime temperatures arising from an inaccurate representation of nocturnal boundary layer processes. The daytime cold bias contrasts with the excessive net radiation flux at the surface by about 50–100 W m−2, underscoring the challenges in the physical representation of land–atmosphere interactions. [ABSTRACT FROM AUTHOR]

The mesoscale dynamics of a record‐breaking Atmospheric River (AR) that impacted the Middle East in mid‐April 2023 and caused property damage and loss of life are investigated using model, reanalysis and observational data. The high‐resolution (2.5 km) simulations revealed the presence of AR rapids, narrow and long convective structures embedded within the AR that generated heavy precipitation (>4 mm hr−1) as they moved at high speeds (>30 m s−1) from northeastern Africa into western Iran. Gravity waves triggered by the complex terrain in Saudi Arabia further intensified their effects. Given the rising frequency of ARs in this region, AR rapids may be even more impactful in a warming climate, and need to be accounted for in reanalysis and numerical models. Plain Language Summary: Atmospheric Rivers (ARs) are narrow and long bands of high water vapor content, which largely originate in the tropics or subtropics and propagate into mid‐ and high‐latitudes. They can bring beneficial rain and snow but, in particular the most intense, can lead to catastrophic flooding and loss of life. One of such occurrences in the Middle East in mid‐April 2023 is investigated using model and observational data. The high‐resolution (2.5 km) simulation put in evidence narrow (5–15 km) and long (100–200 km) convective structures within the AR, known as AR rapids, which produced heavy precipitation (>4 mm hr−1), further enhanced by gravity waves that developed over the high terrain in western Saudi Arabia, and propagated at high speeds (>30 m s−1). ARs are occurring more frequently in the Middle East as they are globally, and with increased atmospheric water vapor in a warming climate, AR rapids may be even more destructive. Key Points: The exceptional and impactful Atmospheric River of mid‐April 2023 in the Middle East is investigated with model and observational dataA 2.5 km simulation reveals the presence of "Atmospheric River rapids," narrow along‐flow structures that generated rain rates >4 mm hr−1Model simulations and ground‐based observations underlined the effects of the Atmospheric River and associated trailing cold front [ABSTRACT FROM AUTHOR]

The Empty Quarter Desert, one of Earth's major dust sources, frequently experiences dust storms due to wind erosion. Despite its significance as a primary dust source on a global scale, in‐situ observations from this region had not been reported until very recently. In summer 2022, the WInd‐blown Sand Experiment (WISE) Phase‐1 was initiated in the Empty Quarter Desert of the United Arab Emirates, and continued until 7 February 2023. Utilizing a diverse array of instruments, we measured winds, temperature, humidity, radiation fluxes, saltation, and the physical and optical properties of dust aerosols, atmospheric electric fields, and soil characteristics. A total of 38 distinct sand‐saltation events were recorded from September 2022 to February 2023, with activity peaking between 13:00 and 14:00 local time. Key findings include the identification of dominant wind patterns, and the measurement of the average aerodynamic roughness length (z0) at 0.8 ± 0.6 mm, and the thermal roughness length (zh) at 0.3 ± 0.5 mm—the first estimation of zh for this area. In‐situ observations revealed that dust particle concentrations near the surface increased 1.7‐fold on days with saltation compared to days without it. Moreover, we determined a wind‐speed threshold for initiating saltation at 7.70 m s−1. This comprehensive data set significantly advances our understanding of atmospheric‐soil interactions and sand movement dynamics, providing invaluable insights for ongoing research into desert environments and the global dust cycle. Plain Language Summary: The Empty Quarter Desert, one of the Earth's major dust sources, frequently experiences dust storms due to wind erosion. Despite its importance as a main dust source on a global scale, no in‐situ observations from this region have been reported until very recently. In the summer of 2022, the WInd‐blown Sand Experiment (WISE) Phase‐1 provided crucial data on the arid environment of the Empty Quarter Desert in the United Arab Emirates. Lasting until February 2023, this experiment focused on quantifying environmental and soil characteristics through an array of measurements, including wind direction and speed, temperature, humidity, radiation fluxes, and dust particle concentrations. The study revealed dominant wind patterns, quantified the aerodynamic and thermal roughness of the desert soil, and recorded 38 distinct sand movement events, noting a peak in activity during early afternoon hours. This research is significant for its detailed analysis of particle concentration changes during these events and its establishment of a specific wind speed threshold for sand movement in this region. These findings are invaluable for researchers studying desert environments, particularly in terms of understanding atmospheric‐soil interactions and the dynamics of sand movement. Key Points: First‐of‐its kind experiment in the Empty Quarter Desert to characterize environmental dynamicsThe first estimation of the thermal roughness length (zh) for this desert and is found to be 0.3 mmThe derived wind‐speed threshold for saltation at the Empty Quarter Desert is 7.70 m s−1 [ABSTRACT FROM AUTHOR]

This study presents a comprehensive evaluation of the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) in simulating meteorological parameters and concentrations of gaseous pollutants across the United Arab Emirates (UAE) for the months of June and December 2018, representing the contrasting climatic conditions of summer and winter. The assessment of WRF-Chem performance involved comparisons with ground-based observations for meteorological parameters and satellite retrievals from the TROPOspheric Monitoring Instrument (TROPOMI) for gaseous pollutants. The assessment of gaseous pollutants using the WRF-Chem model revealed distinct patterns in the estimation of pollutant levels across different areas and seasons. The comparison with TROPOMI column concentration revealed the model's strengths in simulating tropospheric NO2 and total O3 spatio-temporal patterns, although it had deficiencies in modelling the total CO column concentrations. The model exhibited a strong correlation with TROPOMI retrievals, with correlation coefficients ranging between 0.71 and 0.95 for summer and 0.86 to 0.94 for winter among these gaseous pollutants. It tended to slightly overestimate NO2 levels, with a higher discrepancy observed in summer (0.24 x 1015 molecules/cm²) compared to winter (0.19 x 1015 molecules/cm²). When comparing WRF-Chem to TROPOMI-CO data, the discrepancies were more pronounced, showing an overestimation of 0.48 x 1018 molecules/cm² in summer and a significant underestimation of 1.13 x 1018 molecules/cm² in winter. The model consistently underestimated ozone levels in both seasons, by 0.15 x 1018 and 0.20 x 1018 molecules/cm², respectively. Meteorological evaluations revealed the model's tendency to underestimate the 2-m temperature in summer and overestimate it in winter, with mean biases ranging from -2.17 to +1.19 °C and a Root Mean Square Error in the range of 0.8 to 5.9 °C among the stations. The model showed enhanced performance for the 10-m wind speed and downward shortwave radiation flux, reflecting advancements over previous studies. Therefore, the WRF-Chem model effectively simulates key meteorological parameters and pollutants over the UAE, demonstrating significant regional-scale prediction skills. Areas for further model refinement are also identified and discussed. Integrating model predictions with satellite and ground-based data is emphasized for advancing air quality monitoring and enhancing predictive accuracy of atmospheric pollutants in this region. [ABSTRACT FROM AUTHOR]

Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) that caused these record-shattering temperature anomalies. Here, we continue our large collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt that was recorded along coastal areas, but this was outweighed by widespread high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloud-liquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Last, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea ice extent. Significance Statement: Using our diverse collective expertise, we explored the impacts from the March 2022 heat wave and atmospheric river across East Antarctica. One key takeaway is that the Antarctic cryosphere is highly sensitive to meteorological extremes originating from the midlatitudes and subtropics. Despite the large positive temperature anomalies driven from strong downward longwave radiation, this event led to huge amounts of snowfall across the Antarctic interior desert. The isotopes in this snow of warm airmass origin will likely be detectable in future ice cores and potentially distort past climate reconstructions. Even measurements of space activity were affected. Also, the swells generated from this storm helped to trigger the final collapse of an already critically unstable Conger Ice Shelf while further degrading sea ice coverage. [ABSTRACT FROM AUTHOR]

Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of −9.4°C on 18 March at Concordia Station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an intense atmospheric river advecting subtropical/midlatitude heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heat wave's meteorological drivers, impacts, and historical climate context. Here we focus on describing those temperature records along with the intricate meteorological drivers that led to the most intense atmospheric river observed over East Antarctica. These efforts describe the Rossby wave activity forced from intense tropical convection over the Indian Ocean. This led to an atmospheric river and warm conveyor belt intensification near the coastline, which reinforced atmospheric blocking deep into East Antarctica. The resulting moisture flux and upper-level warm-air advection eroded the typical surface temperature inversions over the ice sheet. At the peak of the heat wave, an area of 3.3 million km2 in East Antarctica exceeded previous March monthly temperature records. Despite a temperature anomaly return time of about 100 years, a closer recurrence of such an event is possible under future climate projections. In Part II we describe the various impacts this extreme event had on the East Antarctic cryosphere. Significance Statement: In March 2022, a heat wave and atmospheric river caused some of the highest temperature anomalies ever observed globally and captured the attention of the Antarctic science community. Using our diverse collective expertise, we explored the causes of the event and have placed it within a historical climate context. One key takeaway is that Antarctic climate extremes are highly sensitive to perturbations in the midlatitudes and subtropics. This heat wave redefined our expectations of the Antarctic climate. Despite the rare chance of occurrence based on past climate, a future temperature extreme event of similar magnitude is possible, especially given anthropogenic climate change. [ABSTRACT FROM AUTHOR]

Fog augments the wet deposition of airborne particles entrained in its hydrometeors. This article aims to characterize fog deposition processes around the Barakah nuclear power plant (BNPP), in the United Arab Emirates (UAE), and assess the potential impact of fog on the deposition rate of radionuclides in case of an accidental release. To this end, the microphysics of twelve radiation fog events, typical in such arid climate, were measured during the winter seasons of 2021 and 2022 using a fog monitor that was deployed at the BNPP. The impact of fog deposition on the settling of radionuclides is investigated based on model simulations using the Weather Research Forecasting (WRF) model with the MYJ PBL scheme and FLEXPART. All fog events are found to share a common feature of a bimodal distribution in droplet number concentration (Nc), with modes at 4.5 μ m and 23.16 μ m. It was pointed out that despite the high proportion of smaller droplets in the fog associated with the fine mode, the greatest contribution to the liquid water content (LWC) comes essentially from medium to large droplets between 10 and 35 μ m. The deposition flux of fog water at the site and the fog droplet deposition velocity were estimated using an Eddy Covariance (EC) onsite. Typical mean values for fog droplet deposition velocity are found to range between 2.11 and 7.87 cm s-1. The modeling results show that fog deposition contributed by 30–40 % to the total ground deposition of 137Cs, highlighting the importance of incorporating fog deposition as an additional scavenging mechanism in dispersion modeling under foggy conditions. [ABSTRACT FROM AUTHOR]

Pine Island Glacier (PIG) has recently experienced increased ice loss that has mostly been attributed to basal melt and ocean ice dynamics. However, atmospheric forcing also plays a role in the ice mass budget, as besides lower-latitude warm air intrusions, the steeply sloping terrain that surrounds the glacier promotes frequent Foehn winds. An investigation of 41 years of reanalysis data reveals that Foehn occurs more frequently from June to October, with Foehn episodes typically lasting about 5 to 9 h. An analysis of the surface mass balance indicated that their largest impact is on the surface sublimation, which is increased by about 1.43 mm water equivalent (w.e.) per day with respect to no-Foehn events. Blowing snow makes roughly the same contribution as snowfall, around 0.34–0.36 mm w.e. d -1 , but with the opposite sign. The melting rate is 3 orders of magnitude smaller than the surface sublimation rate. The negative phase of the Antarctic oscillation and the positive phase of the Southern Annular Mode promote the occurrence of Foehn at PIG. A particularly strong event took place on 9–11 November 2011, when 10 m winds speeds in excess of 20 m s -1 led to downward sensible heat fluxes higher than 75 W m -2 as they descended the mountainous terrain. Surface sublimation and blowing-snow sublimation dominated the surface mass balance, with magnitudes of up to 0.13 mm w.e. h -1. Satellite data indicated an hourly surface melting area exceeding 100 km 2. Our results stress the importance of the atmospheric forcing on the ice mass balance at PIG. [ABSTRACT FROM AUTHOR]

In this paper, the feasibility of satellite remote sensing in detecting and predicting locations of buried objects in the archaeological site of Saruq Al-Hadid, United Arab Emirates (UAE) was investigated. Satellite-borne synthetic aperture radar (SAR) is proposed as the main technology for this initial investigation. In fact, SAR is the only satellite-based technology able to detect buried artefacts from space, and it is expected that fine-resolution images of ALOS/PALSAR-2 (L-band SAR) would be able to detect large features (>1 m) that might be buried in the subsurface (<2 m) under optimum conditions, i.e., dry and bare soil. SAR data were complemented with very high-resolution Worldview-3 multispectral images (0.31 m panchromatic, 1.24 m VNIR) to obtain a visual assessment of the study area and its land cover features. An integrated approach, featuring the application of advanced image processing techniques and geospatial analysis using machine learning, was adopted to characterise the site while automating the process and investigating its applicability. Results from SAR feature extraction and geospatial analyses showed detection of the areas on the site that were already under excavation and predicted new, hitherto unexplored archaeological areas. The validation of these results was performed using previous archaeological works as well as geological and geomorphological field surveys. The modelling and prediction accuracies are expected to improve with the insertion of a neural network and backpropagation algorithms based on the performed cluster groups following more recent field surveys. The validated results can provide guidance for future on-site archaeological work. The pilot process developed in this work can therefore be applied to similar arid environments for the detection of archaeological features and guidance of on-site investigations. [ABSTRACT FROM AUTHOR]

Tropical cyclones (TC) are one of the biggest natural hazards with significant threat to life and property due to storm surge, flooding and extreme winds. Combined, these hazards substantially increase the potential for loss of life and damage especially in populated landfall‐locations such as the countries on the Arabian Gulf and Sea of Oman. Hence, it is important to identify the factors that modulate the trajectory of TC in order to better predict their lifetime and dynamics. Since 1900, only two TCs moved into the Sea of Oman and made landfall on the southeastern coast of the Arabian Peninsula (AP): TC Shaheen in 2021 and Gonu in 2007. In this study, the mechanisms behind the exceptional trajectories of these two TCs are investigated. Both TCs developed during the active phase of the Madden‐Julian Oscillation, and benefited from above‐average sea surface temperatures (SSTs), ocean heat content and reduced vertical wind shear. Their paths over the Indian Ocean were controlled by large‐scale forcings, whereas regional‐scale processes, such as the local SST gradients and the Arabian Heat Low (AHL) defined their trajectories near landfall location over the AP. An exceptionally deep AHL was present during these events. The AHL is found to interact two‐way with TCs: its associated circulation drags the TCs inland while the TCs, through the advection of cooler marine‐air inland, cause the collapse of the AHL. It is recommended to account for the AHL as fluctuations in its position and strength can determine where future TCs make landfall. Key Points: Cyclones Shaheen and Gonu developed in the active phase of the Madden‐Julian Oscillation and in a La Nina state in the northern Indian OceanPositive surface and subsurface ocean temperature anomalies fueled the storms and played important role in their pathsAn abnormally deep Arabian Heat Low over the Arabian Peninsula dragged the cyclones inland and modulated their exceptional trajectories [ABSTRACT FROM AUTHOR]

The calving of Antarctic ice shelves remains unpredictable to date due to a lack of understanding of the role of the different climatic components in such events. In this study, the role of atmospheric forcing in the calving of the Brunt Ice Shelf (BIS) in February 2021 is investigated using a combination of observational and reanalysis data. The occurrence of a series of extreme cyclones around the time of the calving induced an oceanward sea‐surface slope of >0.08° leading to the calving along a pre‐existing rift. The severe storms were sustained by the development of a pressure dipole on both sides of the BIS associated with a La Niña event and the positive phase of the Southern Annular Mode. Poleward advection of warm and moist low‐latitude air over the BIS area just before the calving was also observed in association with atmospheric rivers accompanying the cyclones. Immediately after the calving, strong offshore winds continued and promoted the drift of the iceberg A‐74 in the Weddell Sea at a speed up to 700 m day−1. This study highlights the contribution of local atmospheric conditions to ice‐shelf dynamics. The link to the larger scale circulation patterns indicates that both need to be accounted for in the projections of Antarctic ice shelf evolution. Plain Language Summary: A calving event is the process by which a large block of ice gets separated from an ice shelf or glacier and forms an iceberg. Large calving events from marine‐terminating ice shelves around Antarctica remain to date highly unpredictable. This process is typically associated with the glaciological cycle of the ice shelves as well as ocean dynamics. However, atmospheric forcing in triggering such events has been largely overlooked. This is investigated for the calving of iceberg A‐74 from the Brunt Ice Shelf (BIS) in February 2021. We found that strong near‐surface winds associated with intense cyclones promoted the event via an increased sea‐surface slope toward the open ocean, which amplified the stress on the pre‐existing rift and led to the calving. After the calving, the iceberg drifted westwards in the Weddell Sea at a speed of 700 m day−1 aided by strong offshore winds. The extreme weather conditions leading to the calving were associated with an alternation of a series of high (blockings) and low (troughs) pressure systems around the BIS region. Key Points: An intense and stationary cyclone around the ice shelf, which was part of a wave train occurred at the time of the calvingStrong near‐surface winds associated with the cyclone promoted the calving of the Brunt Ice Shelf via oceanward sea‐surface slopeCalving occurred on 26 February when the ice accelerated significantly in a westward direction from a velocity of 4–6 to 700 m day−1 [ABSTRACT FROM AUTHOR]

Accurate simulation of boundary layer surface meteorological parameters is essential to achieve good forecasting of weather and atmospheric dispersion. This paper is devoted to a model sensitivity study over a coastal hyper-arid region in the western desert of the United Arab Emirates. This region hosts the Barakah Nuclear Power Plant (BNPP), making it vital to correctly simulate local weather conditions for emergency response in case of an accidental release. We conducted a series of high-resolution WRF model simulations using different combinations of physical schemes for the months January 2019 and June 2019. The simulated results were verified against in-situ meteorological surface measurements available offshore, nearshore, and inland at 12 stations. Several statistical metrics were calculated to rank the performance of the different simulations and a near-to-optimal set of physics options that enhance the performance of a WRF model over different locations in this region has been selected. Additionally, we found that the WRF model performed better in inland locations compared to offshore or nearshore locations, suggesting the important role of dynamical SSTs in mesoscale models. Moreover, morning periods were better simulated than evening ones. The impact of nudging towards station observations resulted in an overall reduction in model errors by 5–15%, which was more marked at offshore and nearshore locations. The sensitivity to grid cell resolution indicated that a spatial resolution of 1 km led to better performance compared to coarser spatial resolutions, highlighting the advantage of high-resolution simulations in which the mesoscale coastal circulation is better resolved. [ABSTRACT FROM AUTHOR]

With the projected expansion of arid/semi‐arid regions in a warming world, precipitation enhancement activities such as cloud seeding will become increasingly popular and relied upon. Due to the inherent costs, a successful planning is crucial, which involves accurate model predictions. In this study, the usefulness of the Weather Research and Forecasting (WRF) model forecasts for guidance into seeding operations in the United Arab Emirates, where seeding activities have been conducted for more than two decades, is assessed. The WRF predictions are compared with ground‐based, satellite‐derived and radar reflectivity data, and in‐situ observations onboard the airplanes used to perform the seeding operations. WRF is found to have higher skill in simulating the observed cloud top pressure/temperature than the cloud fraction, with the model vertical velocity predictions also more skillful than those of the radar reflectivity. A stronger Arabian Heat Low (AHL) in the model leads to drier conditions which, together with a surface cold bias, limits the spatial extent and vertical depth of the simulated convective clouds. Development of convective rolls in the boundary layer is reported in both observations and simulations and their interaction with cold pools from convective clouds promote the development of secondary convection. Sensitivity to the choice of the Planetary Boundary Layer (PBL) scheme is also noticed, with the Yonsei University PBL scheme giving the best performance. When considering the two factors needed for a successful seeding operation that is, the presence of an updraft and clouds, the model‐predicted seeding regions largely match the areas where precipitation was observed. As the proposed WRF set up can be used operationally, the model forecasts will bring added value to the seeding activities in the country. Key Points: The usefulness of Weather Research and Forecasting model forecasts for cloud seeding activities in the United Arab Emirates is assessedUpdrafts generally weaker in the model due to colder surface, but if the position of cells is accounted for the magnitudes are comparableSeeding regions predicted by the model are in agreement with observed convective regions, and proposed set up can be used operationally [ABSTRACT FROM AUTHOR]

In this article, the climatological state and the seasonal variability of the Arabian heat low (AHL) and the intertropical discontinuity (ITD) are investigated over the Arabian Peninsula using the 1979–2019 ERA‐5 reanalysis data. The AHL is a summertime feature, mostly at 15°–35°N and 40°–60°E, exhibiting a clear strengthening over the last four decades in line with the observed increase in surface temperature. However, no clear shift in its position is detected. The AHL, driven by both thermodynamic and dynamic forcing, is broader and stronger during daytime and exhibits considerable variability on day‐to‐day timescales, likely due to the convection associated with the Asian summer monsoon. The ITD is the boundary between the hot and dry desert air and the cooler and more moist air from the Arabian Sea. It lies along the Arabian Peninsula's southern coastline in the cold season but reaches up to 28°N between 50° and 60°E in the summer months. While in the former it has a rather small diurnal variability; in the latter it shows daily fluctuations of up to 10° in latitude. The presence of the Sarawat Mountains over southwestern Saudi Arabia precludes a northward migration of the ITD in this area. The ITD exhibited a weak northward migration in the 41‐year period, likely due to the increased sea surface temperatures in the Arabian Sea. On inter‐annual timescales, the El Niño‐Southern Oscillation, the Indian Ocean Dipole, and solar‐geomagnetic effects play an important role in the AHL's and ITD's variability. [ABSTRACT FROM AUTHOR]

Fog microphysics characteristics play an important role in fog life cycle, radiation and visibility. Measurements of fog microphysics are important in understanding these processes and improving existing model parameterization schemes. From 28 January to 17 February 2021, we carried out the first measurements of fog microphysics in the arid region of the United Arab Emirates and present initial results in this paper. Five events occurred, the longest lasting about 4 hr 28 min and the remaining lasting 2 hr or less. In this study, the meteorological conditions at synoptic scale associated with the formation of fog, are presented as well as the microphysics characteristics of fog. Maximum cloud droplet count ranged from 80 to 700 cc, Liquid Water Content (LWC) from 0.06 to 0.58 g m−3 and the Median Volume Diameter reached 25 μm in all the cases. The estimated Liquid Water Path reached a maximum of 100 g m−2. The size distribution was bimodal for all visibility classes of mist, fog and thick fog with modes at around 4.5 μm and between 22 and 25 μm. The droplet size distribution broadened as the mature phase progressed, demonstrating a decrease in droplets in the 6–16 μm range and an increase in droplets above 19 μm. During the mature stage, droplet growth was observed with no associated decrease in LWC, suggesting growth by collision and coalescence was occurring. However, LWC did increase concurrently suggesting droplet growth by condensation was also taking place. Plain Language Summary: During the cold season of each year, desert regions experience the formation of radiation fog due to the rapid cooling of the desert surface at night. Cities built on the fringes of major desert regions, such as the United Arab Emirates (UAE) cities, witness very poor visibility due to seasonal fog formation. The fog impacts air and road traffic and disrupts the daily life. Fog microphysics characteristics play a key role in fog life cycle, radiation and visibility. Measurements of fog microphysics are important to understand and improve existing model parameterization schemes for a more accurate forecast of fog occurrence and life cycle. We carried out the first fog microphysics measurements over the UAE, an arid region on the Arabian Peninsula, where fog is a frequent occurrence in winter months. Results from this study are the first of their kind in the region and are expected to advance the current knowledge on fog dynamics and characteristics. Key Points: First microphysical measurements of radiation fog in the United Arab Emirates, a warm, arid region in the subtropicsThe cloud droplet size distribution was bimodal for all visibility classes, with modes at around 4.5 μm and between 22 and 25 µmDroplet growth was observed to be due to collision, coalescence and condensation [ABSTRACT FROM AUTHOR]

The impact of 26 December 2019 annular solar eclipse (ASE) on meteorological conditions over the southeastern Arabian Peninsula is investigated. Observations sourced from the spinning enhanced visible and infrared imager (SEVIRI) and vertical temperature profiles measured by a microwave radiometer were used. The ASE, which began at 03:36:37.9 Universal Time Coordinated (UTC), that is, 31 m 29.9 s after sunrise, left a significant imprint on the land surface temperature (LST). In particular, in some regions, the LST dropped by more than 4 °C, in comparison to the previous day. In situ soil properties, in particular soil texture, were also found to have modulated the effects of the ASE, with loamy soils experiencing higher heating/cooling rates than sandy soils. Finally, the analysis of atmospheric profiles indicated that the eclipse influenced the flow throughout the atmospheric boundary layer, with a stable layer that was 45-min longer and 90-m deeper compared with the preceding day. [ABSTRACT FROM AUTHOR]

The Weather Research and Forecasting (WRF) model is used to investigate convection-aerosol interactions in the United Arab Emirates for a summertime convective event. Both an idealised and scaled versions of a 7-year climatological aerosol distribution are considered. The convection on 14 August 2013 was triggered by the low-level convergence of the circulation associated with the Arabian Heat Low (AHL) and the daytime sea-breeze circulation. The cold pools associated with the convective events, as well as the low-level wind convergence along the Intertropical Discontinuity (ITD) earlier in the day, explain the dustier environment, with Aerosol Optical Depths (AODs) in excess of two. Due to a colder surface and air temperature, the AHL is incorrectly represented in WRF, which leads to a mismatch between the observed and modelled clouds and precipitation. Employing interior nudging in the outermost grids of the three-nested simulation has a small but positive impact on the model predictions of the innermost nest. This is because the higher temperatures from more accurate boundary conditions are offset by colder temperatures from locally enhanced precipitation, the latter arising from a shift in the position of the AHL. Numerical experiments revealed a high sensitivity to the aerosol properties. In particular, replacing 20 % of the rural aerosols by carbonaceous particles has an impact on the surface radiative fluxes comparable to increasing the aerosol loading by a factor of 10, with a daily-averaged reduction in the UAE-averaged net shortwave radiation flux of ~90 W m-2 and an increase in the net longwave radiation flux of ~51 W m-2. However, in the former, WRF generates 20 % more precipitation than in the latter, due to a broader and weaker AHL. The surface downward and upward shortwave and upward longwave radiation fluxes are found to scale linearly with the aerosol loading, while the downward longwave radiation flux varies by less than ±12 W m-2 when the aerosol amount and/or properties are changed. An increase in the aerosol loading also leads to drier conditions due to a shift in the position of the AHL and rainfall occurring in a drier region, with a domain-wise decrease in the daily accumulated rainfall of 16 % when the aerosol loading is increased by a factor of 10. In addition, the onset of convection is also delayed. [ABSTRACT FROM AUTHOR]

This study provides insights on the composition and variability of atmospheric aerosols over the United Arab Emirates (UAE) by analyzing the atmospheric conditions together with 14 years (2006–2019) of aerosol optical depth (AOD) retrieved from CALIPSO (Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite, and 7 years of AOD measured from the ground‐based Aerosol Robotic Network (AERONET). We found that mineral dust is the most prevailing aerosol subtype. In addition, polluted dust and polluted continental aerosols are observed mostly in the cold season. The AOD is higher in spring and summer, when the atmospheric conditions are more favorable to the occurrence of dust events. Moreover, there is another peak in winter associated with dust storms triggered by mid‐latitude baroclinic systems. In summer's daytime, extinction coefficients in excess of 0.2 km−1 are observed up to 3–4 km above the surface, as a result of the warmer and windier conditions. In the cold season and at night, the dust layers are confined to the lower atmosphere below 2 km. On a climatological time scale, we found that the AOD over the UAE has been decreasing since 2009, possibly due to the increasing trend in precipitation and changes in land use. This study highlights the large contribution of dust aerosols to the total aerosol load over the UAE and stresses on the need to account for mineral dust aerosols in climate‐air pollution related studies as well as weather and air quality forecasts. Key Points: Over the UAE, dust is the prevailing aerosol subtype, polluted dust and polluted continental aerosols are also observed mostly in winterIn summer, aerosols are observed up to 3–4 km above the surface, due to a deeper boundary layer. In winter they are confined below 2 kmAOD is higher in spring and summer and it has been decreasing since 2009 in correlation with positive precipitation trends [ABSTRACT FROM AUTHOR]

Ice shelf instability is one of the main sources of uncertainty in Antarctica's contribution to future sea level rise. Calving events play a crucial role in ice shelf weakening but remain unpredictable, and their governing processes are still poorly understood. In this study, we analyze the unexpected September 2019 calving event from the Amery Ice Shelf, the largest since 1963 and which occurred almost a decade earlier than expected, to better understand the role of the atmosphere in calving. We find that atmospheric extremes provided a deterministic role in this event. A series of anomalously deep and stationary explosive twin polar cyclones over the Cooperation and Davis seas generated tides and wind-driven ocean slope, leading to fracture amplification along the pre-existing rift and ultimately calving of the massive iceberg. The calving was triggered by high oceanward sea surface slopes produced by the storms. The observed record-anomalous atmospheric conditions were promoted by blocking ridges and Antarctic-wide anomalous poleward transport of heat and moisture. Blocking highs helped in (i) directing moist and warm air masses towards the ice shelf and (ii) maintaining the observed extreme cyclones stationary at the front of the ice shelf for several days. Accumulation of cold air over the ice sheet, due to the blocking highs, led to the formation of an intense cold high pressure over the ice sheet, which helped fuel sustained anomalously deep cyclones via increased baroclinicity. Our results stress the importance of atmospheric extremes in ice shelf dynamics via tides and sea surface slope and its need to be accounted for when considering Antarctic ice shelf variability and contribution to sea level, especially given that more of these extremes are predicted under a warmer climate. [ABSTRACT FROM AUTHOR]

A summertime convective event that developed on 5 September 2017 over the United Arab Emirates (UAE) is investigated in this study. Atmospheric profiles from a ground‐based microwave radiometer along with satellite observations and in situ data from three weather stations in the UAE were used. The event was simulated using the Weather Research and Forecasting (WRF) model, forced with four input datasets: Global Forecast System (GFS), Climate Forecast System Reanalysis (CFSR), and the European Centre for Medium‐Range Weather Forecasts ERA‐5 and ERA‐Interim reanalyses. The afternoon and evening convection was triggered by the intrusion of a mid‐level trough from midlatitudes and was favoured by the convergence over land of thermally forced maritime air masses. Near‐surface observations at a weather station revealed a 7 °C drop in air temperature, a doubling of the wind speed to 9 m·s−1 in 30 min, and a shift in wind direction from easterly, to southerly and then westerly in about 45 min, associated with the passage of the cold pool emanating from a Mesoscale Convective System (MCS). At the location where the microwave radiometer was deployed, the pre‐squall low and wake low signatures are also captured, with a 5 m·s−1 increase in the wind speed in just 5 min. The observed features of the studied MCS were found to compare with those reported for MCSs in the Tropics. The four experiments gave a similar performance, although the GFS simulation generally generated higher skill scores. The investigated MCS event was not captured by WRF, which was attributed to a misrepresentation of soil moisture in the model. This study highlights the difficulties regional models like WRF may have in reproducing MCSs over arid/hyperarid regions, which may result in a misrepresentation of their impacts in climate projection studies. [ABSTRACT FROM AUTHOR]

This study investigates the atmospheric dynamics of the major dust storm that occurred in June 2020 over the Sahara and during which dust clouds associated with the highest‐on‐record aerosol optical depths were transported toward the America. An anomalous atmospheric circulation pattern in the mid‐latitudes, linked to a circumglobal wavetrain, resulted in the development of a subtropical high‐pressure system to the west of the Saharan heat low. This created a pressure dipole and generated anomalously strong northeasterlies over the Sahara, which caused continuous dust emissions over 4 days. Occurring along the northern fringes of the intertropical discontinuity, the dust was transported to higher altitudes (6 km) by the strong updraft in this region. This injected the dust at the African Easterly Jet (AEJ) altitudes and favored a rapid westward long‐range transport. The AEJ was also anomalously strong, being strengthened by the anticyclonic circulation associated with the anomalous high. Plain Language Summary: Dust is an important constituent of the Earth's atmosphere, with a wide range of impacts ranging from human health to effects on climate. In June 2020, massive amounts of dust were lifted from the Sahara, the major dust source region in the world, and transported all the way into the Americas across the tropical Atlantic Ocean. This event was caused by the development of a subtropical high‐pressure system over northwest Africa which resulted in sustained strong northeasterlies over the Sahara generating continuous dust emissions for 4 days. Due to the strong low‐level convergence along the intertropical discontinuity region, the dust was lifted to roughly 5–6 km above the surface, and then transported westward by the stronger mid‐atmospheric winds (>20 m s−1). At Cape Verde and over large swaths of the Atlantic Ocean, the amount of dust suspended in the atmosphere was associated with the largest aerosol optical depths on record. Key Points: The dust storm was triggered by the development of a subtropical high off the coast of West Africa embedded in a circumglobal wavetrainThe stationary subtropical high increased the north‐south pressure gradient over the Sahara and generated sustained strong northeasterliesThe anticyclonic circulation associated with the high intensified the African Easterly Jet favoring a rapid westward transport of the dust plumes [ABSTRACT FROM AUTHOR]

Over the 40‐year satellite record, there has been a slight increasing trend in total annual mean Antarctic sea ice extent of approximately 1.5% per decade that is made up of the sum of significantly larger opposing regional trends. However, record increases in total Antarctic sea ice extent were observed during 2012–2014, followed by record lows (for the satellite era) through 2018. There is still no consensus on the main drivers of these trends, but it is generally believed that the atmosphere plays a significant role and that seasonal time scales and regional scale processes are important. Despite considerable yearly and regional variability, the mean seasonal cycle of growth and melt of Antarctic sea ice is strikingly consistent, with a slow growth but fast melt season. If we are to project trends in Antarctic sea ice and understand changes on longer time scales, we need to understand the mechanisms related to the seasonal cycle separately from those that drive variability. Twice‐yearly changes in the position and intensity of the zonal winds circling Antarctica are thought to drive the system by working with or against the evolving sea ice edge to slow the autumn advance and hasten the spring melt. Open water regions, created by divergence associated with the zonal winds, amplify the spring melt through increased warming of the upper ocean. Climate models fail to accurately reproduce mean Antarctic sea ice extent and overestimate its year‐to‐year variability, but they tend to capture the pattern and timing of the Antarctic seasonal cycle. Plain Language Summary: Antarctic sea ice extent has been observed daily from satellites over the last 40 years. Compared to the Arctic, there has been little overall change in Antarctic sea ice cover over this time. However, the slightly increasing trend masks substantial interannual and regional variability, and recent years have seen record increases (2012–2014) followed by record lows (through 2018). Despite this variability, the pattern of growth and melt of total Antarctic sea ice shows a consistent, asymmetric cycle with slow growth but rapid melt periods. The presence of many individual storms around the continent gives rise to a band of low pressure that circles the continent, and this low‐pressure band marks a boundary between westerlies to the north and easterlies to the south. Twice‐yearly changes in the position and intensity of these zonal winds work with or against the evolving ice edge to slow the autumn advance and hasten the spring retreat. Open water areas created in the spring lead to increased warming of the upper ocean, which also acts to speed up the spring retreat. On the whole, climate models tend to capture the pattern and timing, but not the magnitude, of the Antarctic seasonal cycle. Key Points: Antarctic sea ice has a remarkably consistent, asymmetric annual cycle, despite substantial interannual variabilityZonal winds work with or against the evolving position of the ice edge, and ice‐ocean albedo feedback amplifies the sea ice seasonal cycleClimate models tend to capture the pattern and timing of the Antarctic seasonal cycle but not the magnitude [ABSTRACT FROM AUTHOR]

This study examines the role of atmospheric forcings in the occurrence of open‐ocean polynyas by investigating the case of the austral winter 2017's polynya located in the Lazarev Sea sector to the east of the Weddell Sea, known as the Maud Rise polynya or the Weddell Polynya. The ice‐free zone appeared in mid‐September 2017 and grew to as large as 80,000 km2 by the end of October 2017 before merging with the open ocean after the sea ice started to retreat at the beginning of the austral summer. Using a combination of satellite observations and reanalysis data at high spatiotemporal resolution, we found that severe cyclones, occurring over the ice pack, have a deterministic role in creating strong divergence in the sea ice field through strong cyclonic surface winds leading to the opening of the polynya. The occurrence of intense and frequent cyclones over the ice pack during austral winter 2017 was unusual, and it occurred under an enhanced strong positive meridional transport of heat flux and moisture toward Antarctica associated with an amplification of the atmospheric zonal wave 3 and a strong positive Southern Annular Mode index. We found that the opening of the polynya was not primarily due to direct ice melt by thermodynamic effects but rather to strong dynamical forcing by the winds on the sea ice, as in the case of coastal polynyas. Indeed, the meridional transport of heat toward Antarctica occurred over the Weddell Sea sector (i.e., to the east of the Lazarev Sea sector where the polynya is located) whereas the Lazarev Sea sector was under the influence of equatorward transport of cold air masses at that time. Our results show that the supply of warm and moist air coming from the west side of the South Atlantic Ocean into the Weddell Sea significantly increased the potential for cyclone formation as measured by the Eady growth rate leading to intense and frequent cyclogenesis over the ice pack, far south from the ice edge. After cyclogenesis in the Weddell Sea, these cyclones intensified as they moved eastward spinning over the Lazarev Sea with intensity comparable to category 11—violent storms—in the Beaufort scale. The cyclonic winds generated sea ice divergence by pushing the ice away from the cyclone center: To the east, north of it and to the west, south of it, which led to the reoccurrence of the Maud Rise polynya in mid‐September 2017. Key Points: Severe cyclones occurring over the ice pack have a deterministic role in the opening of midsea polynyasStrong cyclonic winds caused sea ice divergence, triggering the reoccurrence of the Maud Rise polynya in September 2017The formation of intense and frequent cyclones over the ice pack occurred under an amplified atmospheric zonal wave 3 pattern [ABSTRACT FROM AUTHOR]

During 2017 Austral winter, an open ocean polynya appeared in the Lazarev Sea, centered over Maud Rise. The vertical structure of the water column presented temporal and spatial variability with a weak stratification during the period of observations from January 2015 to January 2019. While over the Northern Maud Rise area, a highly stratified layer was identified between 80-180 m depth. This layer works as a thermal barrier where the energy from summer months is stored, preventing the warm sub-surface waters from mixing with the shallow waters. So far, a complete description of the polynya formation and maintenance processes is still lacking. To characterize the internal structure of the ocean during the 2017 Maud Rise polynya event we use in situ observations and ocean model reanalysis data. The obtained results revealed that the incidence of thermobaric convection, diapycnal and isopycnal mixing processes over the Maud Rise drives the exchange of energy in the water column. We highlight three relevant factors that contribute to the energy flux for the open-ocean polynya preconditioning: level of instability, pycnocline fluctuation, and bathymetric influence. Another remarkable feature is the warmer summer surface layer over the Maud Rise, which transfers heat to intermediate layers accumulating energy for almost four months. Energy storage at the thermal barrier is evaluated based on heat flux calculations to quantify the exchange of energy between the different water layers. These processes together operate as an ocean preconditioning to the formation and maintenance of an open-ocean polynya event. [ABSTRACT FROM AUTHOR]

In this study, we identify a new mechanism by which dust aerosols travel over long distances across the eastern side of the North Atlantic Ocean toward the Arctic. The meandering polar jet was at the origin of both dust emission through cyclogenesis over Northwest Africa and poleward transport of the uplifted dust towards the Arctic, through cut-off circulation. The dust emission was associated with an intense Saharan cyclone that formed over Northwest Africa in early April 2011. The formation of the cyclone was caused by the intrusion into subtropics, of a high-latitude-upper-level trough, linked to the meandering polar jet. The trough initiated cyclogenesis over Northwest Africa after orographic blocking by the Anti-Atlas Mountains. The still meandering polar jet led to the formation of a cut-off low further south with which the Saharan dust-cyclone merged 2 d later and moved northward with the main stream. Beside satellite observations, a simulation at high resolution was performed using the prognostic-dust permitting model MesoNH. The total dust load carried during this event to areas located north of 40 ∘ N was estimated by the model to be 38 Tg and dust deposition was estimated to be 1.3 Tg. The Saharan dust reaching Greenland was accompanied by warm and moist air masses that caused a rise in surface temperature of about 10 ∘ C for more than 3 consecutive days over the southeastern Greenland. Ice melt over this area of Greenland was detected in the brightness temperature observations. [ABSTRACT FROM AUTHOR]

Background/objective Fixed flexion deformity of the proximal interphalangeal joint can commonly occur following a traumatic injury impacting on hand function and occupational performance. Numerous interventions have been proposed for fixed flexion deformity resolution. This paper investigates the efficacy of static or dynamic orthoses in reducing fixed flexion deformity contracture following traumatic proximal interphalangeal joint injury. Methods A multi-database search of three databases (CINAHL, EMBASE, MEDLINE) was conducted. Data extracted for each study were design, patient descriptions, degree of fixed flexion deformity pre- and post-orthoses, and prescribed interventions and exercise programmes. Results The search yielded 643 studies, of which eight met the inclusion criteria. Studies used heterogeneous methodologies investigating various orthotic interventions. Meta-analysis or pooling of results was not possible. Dissimilar orthotic wear regimes were noted in all studies and an alternative clinical significance outcome was found. Conclusion More research is required to support clinical reasoning in orthotic choice for fixed flexion deformity of the proximal interphalangeal joint post-traumatic injury. [ABSTRACT FROM AUTHOR]