Operational cloud seeding programs have been increasingly deployed in several countries to augment natural rainfall amounts, particularly over water-scarce and arid regions. However, evaluating operational programs by quantifying seeding impacts remains a challenging task subject to complex uncertainties. In this study, we investigate seeding impacts using both long-term rain gauge records and event-based weather radar retrievals within the framework of the United Arab Emirates (UAE) National Center of Meteorology’s operational cloud seeding program. First, seasonal rain gauge records are inter-compared between unseeded (1981–2002) and seeded (2003–2019) periods, after which a posteriori target/control regression is developed to decouple natural and seeded rainfall time series. Next, trend analyses and change point detection are carried out over the July-October seeding periods using the modified Mann-Kendall (mMK) test and the Cumulative Sum (CUSUM) method, respectively. Results indicate an average increase of 23% in annual surface rainfall over the seeded target area, along with statistically significant change points detected during 2011 with decreasing/increasing rainfall trends for pre-/post-change point periods, respectively. Alternatively, rain gauge records over the control (non-seeded) area show non-significant change points. In line with the gauge-based statistical findings, a physical analysis using an archive of seeded (65) and unseeded (87) storms shows enhancements in radar-based storm properties within 15–25 min of seeding. The largest increases are recorded in storm volume (159%), area cover (72%), and lifetime (65%). The work provides new insights for assessing long-term seeding impacts and has significant implications for policy- and decision-making related to cloud seeding research and operational programs in arid regions.

The first 10 days of September 2015 were marked by intense dust activity over the Middle East and the Arabian Peninsula. This study examines the atmospheric conditions at the origin of the large dust storms during this period. We particularly investigate the atmospheric dynamics leading to the development of a large dry cyclone over Iraq on 31 August 2015 which in turn generated an intense dust storm that affected most of the countries around the Arabian Gulf and lasted for 5 days. We found that the cyclone developed over Northwest Iraq as a transfer to low levels of a cut-off low which had formed two days earlier at upper levels over Turkey. Large dust loads exceeding 250 tons were emitted and moved southeast in a cyclonic shape toward the Arabian sea. The second large dust storm on 6-8 September 2015 occurred over Syria and affected all the coastal countries on the eastern side of the Mediterranean Sea. It was associated with the occurrence of a series of density currents over northeast Syria emanating from deep convection over the mountainous border between Syria and Turkey. The unusual development of deep convection over this area was associated with a blocking high and interaction with orography. Both the cut-off high and the cut-off low occurred during a period characterized by a meandering polar jet and an enhanced subtropical jet causing unstable weather over mid-latitudes which in turn led to highly polluted atmosphere by natural dust in the affected countries.

An intense rainfall event affected the United Arab Emirates (UAE) between 15 and 16 April 2024. This study investigated the atmospheric conditions responsible for the formation of large convective storms during this period. Specifically, we analyzed the atmospheric dynamics and large-scale flow that led to the development of a cut-off low-pressure system (COL) over the Arabian Peninsula on 15 April 2024, triggering a two-day period of intense precipitation over the UAE. Our findings indicate that the storms were driven by upper-air instability, a prolonged moisture influx from the monsoon system into the UAE, and the presence of a surface front. Some regions recorded over 200 mm of precipitation within this period, resulting in flash floods, infrastructure disruptions, and significant impacts on the local population. The unusual development of the rainfall event was linked to the displacement of the subtropical jet (STJ), which facilitated the formation and intensification of a COL traversing the region.

This study investigates the underlying atmospheric dynamics associated with intense dust storms in summer 2018 over the Arabian Peninsula (AP); a major dust source at global scale. It reports, for the first time, on the formation of cyclone over the Empty Quarter Desert as important mechanism for intense dust storms over this source region. The dust direct and semi-direct radiative forcings are observed, for the first time over this source region, using high-resolution in-situ and CERES-SYN satellite observational data. The three-dimensional structure and evolution of the dust storms are inferred from state-of-the-art satellite products such as SEVIRI, AEROIASI and CALIPSO. The dynamics and thermodynamics of the boundary layer during this event are thoroughly analyzed using ERA5 reanalysis and ground based observations.We found that a large dust storm by Shamal winds led up, through radiative forcing, to cyclone development over the Empty Quarter Desert, subsequent dust emissions, development of convective clouds and rain. The cyclogenesis over this region initiated a second intense dust storm which developed and impacted the AP for 3 consecutive days. The uplifted dust by the cyclone reached 5 km in altitude and altered the radiative budget at the surface, inducing both significant warming during night and cooling during day. The dust load uplifted by the cyclone was estimated by the mesoscale model Meso-NH to be in the order of 20 Tg, and the associated aerosol optical depth was higher than 3. The model simulates reasonably the radiative impact of the dust in the shortwave but highly underestimated its impact in the LW.Our study stresses the importance of the dust radiative forcing in the longwave and that it should be accurately accounted for in models to properly represent the impact of dust on the Earth system especially near source areas. Missing the warming effect of dust aerosols would impact both the weather and air quality forecast, and the regional climate projections.These results were published in November 2020 in the journal Atmospheric Research doi.org/10.1016/j.atmosres.2020.105364.

Coupling between the polar and subtropical jet streams resulted in jet superposition and attendant upper-tropospheric divergence over the Arabian Peninsula, coincident with a southeastward-advancing Cut-Off Low (COL). On 12 February 2024, the associated convective system generated widespread, surface-verified hailfall across parts of the United Arab Emirates (UAE). This study examines the synoptic- and mesoscale evolution of this event using ECMWF operational analyses, CAMS reanalysis data, radiosonde soundings, satellite remote-sensing products, and radar-derived hail diagnostics. In view of the extensive regional dust plume present in the pre-convective environment, CAMS aerosol fields were analysed to assess the degree to which elevated dust layers modulated thermodynamic stability and moisture transport throughout the event. A COL developed south of Iraq, propagated southeastward, and subsequently interacted with a low-level baroclinic zone. Moisture advection from the Red Sea and the Arabian Sea was mediated by the Red Sea Trough (RST), thereby enhancing atmospheric instability. After an initial weakening stage, associated with mid-tropospheric drying and reduced low-level inflow, the convective system underwent re-intensification over the Arabian Gulf. Radiosonde observations from Abu Dhabi at 0000 UTC on 12 February indicated near-saturated conditions from the surface up to approximately 500 hPa, overlain by a comparatively dry mid-tropospheric layer. Concurrent EUMETSAT RGB composite imagery—optimized to depict dry-air intrusions and jet-related structures—exhibited upper-tropospheric signatures consistent with renewed deep convective development. Radar-derived hail products demonstrated that the period of most prolific hail production coincided with the convective system’s mature stage, during which Hail Mass Aloft (HMA, > 100 kilotons) and Vertically Integrated Hail Mass (VIHM, > 2 kg m⁻²) exceeded operational thresholds typically associated with a high probability of hail reaching the surface. The prevailing thermodynamic and microphysical environment was favourable for substantial hail deposition at the ground, whereas aerosol–radiation interactions appeared to be of secondary importance and did not exert a material influence on storm evolution relative to jet dynamics and moisture transport.

Between 15 and 16 April 2024, an intense rainfall event affected the United Arab Emirates (UAE). This study investigates the atmospheric conditions responsible for the formation of large convective storms during this period. Specifically, we analyze the atmospheric dynamics and large-scale flow that led to the development of a cut-off low-pressure (COL) system over the Arabian Peninsula on 15 April 2024, triggering a two-day period of intense precipitation over the UAE. Our findings indicate that the storms were driven by upper-air instability, a prolonged moisture influx from the monsoon system into the UAE, and the presence of a surface front. Some regions recorded over 200 mm of precipitation within this period, resulting in flash floods, infrastructure disruptions, and significant impacts on the local population. The unusual development of the rainfall event was linked to the displacement of the subtropical jet, which facilitated the formation and intensification of a COL system traversing the region.