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Abstract. The international collaborative Radio Occultation Modeling EXperiment (ROMEX) project marks the first time using a large volume of real data to assess the impact of increased Global Navigation Satellite System (GNSS) radio occultation (RO) observations beyond current operational levels, moving past previous theoretical simulation-based studies. The ROMEX project enabled the use of approximately 35,000 RO profiles– nearly triple the number typically available to operational centers, which is about 8,000 to 12,000 per day. This study investigates the impact of increased RO profiles on numerical weather prediction (NWP) with the Joint Effort for Data assimilation Integration (JEDI) and the global forecast system (GFS), as part of the ROMEX effort. A series of experiments were conducted assimilating varying amounts of RO data along with a common set of other key observations. The results confirm that assimilating additional RO data further improves forecasts across all major meteorological fields, including temperature, humidity, geopotential height, and wind speed, for most of vertical levels. These improvements are significantly evident in verification against both critical observations and the European Center for Medium-Range Weather Forecasts (ECMWF) analyses, with beneficial impacts lasting up to five days. Conversely, withholding RO data resulted in forecast degradations. The results also suggest that forecast improvements scale approximately logarithmically with the number of assimilated profiles, and no evidence of saturation was observed. Biases in the forecast of temperature and geopotential height over the lower stratosphere are discussed, and they are consistent with findings from other studies in the ROMEX community. 

This study’s objective is to better specify the rare occurrence of super equatorial plasma bubbles in particular to the European longitude sector, detailing their spatio-temporal evolution, and better understanding pre-conditions for their development. Our comprehensive multi-instrument analysis combined ground-based and space observations from GNSS, ionosondes, and several satellite missions (COSMIC-2, GOLD, Swarm). We have investigated the ionospheric response to the 23–24 April 2023 severe geomagnetic storm and have shown the formation of super plasma bubbles expanding from equatorial latitudes to middle latitudes in the European/African sector during the main phase of the storm. Formation of these super bubbles was associated with storm-induced prompt penetration electric fields. We found that the area affected by the formation of numerous plasma bubbles covered more than 5000 km ranging from 30°W to 30°E in the Atlantic/African sector. The bubbles also had an impressive north-south extension, reaching as far poleward as ~30°–35° latitude in both hemispheres. After 20 UT on 23 April 2023, the zone with equatorial ionospheric irregularities reached Northern Africa, the Iberian Peninsula (Spain, Portugal) and the Mediterranean Sea in southern Europe, including areas of the Canary Islands (Spain) and the Azores and Madeira Islands (Portugal) in the Atlantic Ocean. The ionospheric irregularities persisted for 5–6 h and began to fade after ~01 UT on 24 April 2023. COSMIC-2 scintillation measurements showed intense amplitude scintillations (S4 above 0.8) across this entire region, indicating presence of small-scale ionospheric irregularities inside the extended plasma bubbles. During this storm, EGNOS (European Geostationary Navigation Overlay Service) experienced degraded performance, with significant navigation errors recorded at its southernmost stations in Northern Africa, Spain, Portugal, and their territories, which were affected by super plasma bubbles. This paper presents conclusive observational evidence showing development of the super plasma bubbles significantly expanding into the southern Europe and northern Africa region under geomagnetically disturbed conditions in April 2023. 

Using the high-rate phase and amplitude scintillation data from FORMOSA7/COSMIC two mission and back-propagation method, we geolocate plasma irregularities that cause scintillations. The results of geolocation are compared with the NASA GOLD UV image data of plasma bubbles. The root mean square of the zonal difference between estimated locations of plasma irregularities and plasma bubbles are about 1.5° and for single intersection cases 0.5° in the magnetic longitude. The geolocation data provide more accurate scintillation location around the globe compared to assigning to the tangent point and is valuable space weather product, which will be routinely available for public use. 

Abstract Interannual variability of tropospheric moisture and temperature are key aspects of Earth’s climate. In this study, monthly mean specific humidity ( q ) and temperature ( T ) variability is analyzed using 12 years of COSMIC-1 (C1) radio occultation retrievals between 60°N and 60°S, with a focus on the tropics. C1 retrievals are relatively independent of the a priori values for q and T within the lower/middle troposphere and upper troposphere/lower stratosphere, respectively. Tropical interannual variability is dominated by El Niño–Southern Oscillation (ENSO). Systematic increases and decreases in zonal mean q and T are observed during the 2009/10 and 2015/16 El Niño events and 2007/08 and 2010/11 La Niña events, respectively. ENSO patterns in q and T are isolated using linear regression, and anomaly magnitudes increase with altitude, reaching a maximum in the upper troposphere. Upper-tropospheric q anomalies expand from the tropics into the midlatitude lower stratosphere, and the T vertical structure is consistent with a moist adiabatic response. C1 results are compared with NCAR’s Whole Atmosphere Community Climate Model (WACCM), forced by observed sea surface temperatures, to evaluate model behavior in an idealized setting. WACCM ENSO variations in q and T generally show consistent behavior with C1 with somewhat smaller magnitudes. Case studies are conducted for major ENSO events during the study period. The spatial variability of q is closely aligned with outgoing longwave radiation (OLR) anomalies. For example, midtropospheric q increases over 100% and OLR decreases over 50 W m −2 over the central Pacific during the 2015/16 El Niño, and substantial regional q and T anomalies are observed throughout the tropics and midlatitudes for each event. 

Abstract Superrefraction at the top of the atmospheric boundary layer introduces problems for assimilation of radio occultation data in weather models. A method of detection of superrefraction by spectral analysis of deep radio occultation signals introduced earlier has been tested using 2 years of COSMIC-2/FORMOSAT-7 radio occultation data. Our analysis shows a significant dependence of the probability of detection of superrefraction on the signal-to-noise ratio, which results in a certain sampling nonuniformity. Despite this nonuniformity, the results are consistent with the known global distribution of superrefraction (mainly over the subtropical oceans) and show some additional features and seasonal variations. Comparisons to the European Centre for Medium-Range Weather Forecasts analyses and limited set of radiosondes show reasonable agreement. Being an independent measurement, detection of superrefraction from deep radio occultation signals is complementary to its prediction by atmospheric models and thus should be useful for assimilation of radio occultation data in the atmospheric boundary layer.