Added-value of GEO-hyperspectral Infrared Radiances for Local Severe Storm Forecasts Using the Hybrid OSSE Method

High spectral resolution (or hyperspectral) infrared (IR) sounders onboard low earth orbiting satellites provide high vertical resolution atmospheric information for numerical weather prediction (NWP) models. In contrast, imagers on geostationary (GEO) satellites provide high temporal and spatial resolution which are important for monitoring the moisture associated with severe weather systems, such as rapidly developing local severe storms (LSS). A hyperspectral IR sounder onboard a geostationary satellite would provide four-dimensional atmospheric temperature, moisture, and wind profiles that have both high vertical resolution and high temporal/spatial resolutions. In this work, the added-value from a GEO-hyperspectral IR sounder is studied and discussed using a hybrid Observing System Simulation Experiment (OSSE) method. A hybrid OSSE is distinctively different from the traditional OSSE in that, (a) only future sensors are simulated from the nature run and (b) the forecasts can be evaluated using real observations. This avoids simulating the complicated observation characteristics of the current systems (but not the new proposed system) and allows the impact to be assessed against real observations. The Cross-track Infrared Sounder (CrIS) full spectral resolution (FSR) is assumed to be onboard a GEO for the impact studies, and the GEO CrIS radiances are simulated from the ECMWF Reanalysis v5 (ERA5) with the hyperspectral IR all-sky radiative transfer model (HIRTM). The simulated GEO CrIS radiances are validated and the hybrid OSSE system is verified before the impact assessment. Two LSS cases from 2018 and 2019 are selected to evaluate the value-added impacts from the GEO CrIS-FSR data. The impact studies show improved atmospheric temperature, moisture, and precipitation forecasts, along with some improvements in the wind forecasts. An added-value, consisting of an overall 5% Root Mean Square Error (RMSE) reduction, was found when a GEO CrIS-FSR is used in replacement of LEO ones indicating the potential for applications of data from a GEO hyperspectral IR sounder to improve local severe storm forecasts.

Condições de tempo severo e formação de tornado em Brasília-DF: um estudo de caso

Os danos ambientais e estruturais causados por uma tempestade severa e tornado associado na área do Aeroporto Internacional de Brasília (DF) no dia 01 de outubro de 2014 motivaram a realização desta pesquisa. A ocorrência do tornado de intensidade F0 (escala Fujita), um fenômeno pouco frequente no Centro-Oeste do Brasil, evidencia a importância de estudos que possibilitem compreender melhor os padrões atmosféricos que favorecem o desenvolvimento de sistemas convectivos severos na região. O objetivo deste trabalho foi identificar fatores ambientais potencialmente favoráveis à manutenção ou dissipação da convecção profunda. A técnica estatística da Análise de Componentes Principais (ACP), dados meteorológicos de superfície e de ar superior e imagens de um radar meteorológico banda-S localizado no Gama-DF foram os principais recursos disponíveis para esta pesquisa. Os resultados indicam que a coexistência de alta instabilidade potencial, temperaturas elevadas e ventos intensos foi determinante para a evolução da tempestade severa. Os índices de instabilidade analisados apresentam valores que diferem consideravelmente dos limiares normalmente utilizados como indicadores da formação de tornados. Linhas de instabilidade em forma de arco (“bow echoes”) detectadas pelo radar meteorológico durante o período de chuva intensa com danos em superfície são os indícios mais fortes do tornado que atingiu a região. Registros fotográficos de linhas de transmissão de energia elétrica, telhados, árvores e carros danificados pelo vento (95 km/h) também são relevantes na caracterização do fenômeno.Severe weather conditions and tornado formation in Brasília-DF: a case study A B S T R A C TThe environmental and structural damages caused by a severe storm and associated tornado in the area of the International Airport of Brasília (DF) on 01 October 2014 motivated this research. The occurrence of the F0 intensity tornado (Fujita scale), an infrequent phenomenon in Central-West Brazil, highlights the importance of studies that allow a better understanding of the atmospheric patterns that favor the development of severe convective systems in the region. In this context, the objective in this work was to identify environmental factors that are potentially favorable to the maintenance or dissipation of deep convection. The statistical technique of Principal Component Analysis (PCA), meteorological surface and upper air data and Gama-DF S-band meteorological radar images were the main resources available for this research. The results indicate that the coexistence of high instability potential, high temperatures and strong winds was fundamental for the severe storm evolution. The instability indices show values that differ considerably from the limits normally used as indicative of tornado formation. Arc-shaped squall lines (“bow echoes”) detected by the meteorological radar during the intense rainfall period with surface damages are the strongest signatures of the tornado that hit the region. Photographic evidences of damages on transmission lines of electricity, roofs, trees and cars caused by the winds (95 km/h) are also relevant in the phenomenon characterization.Keywords: tornado, bow echo, squall line, Principal Component Analysis.

Unusually high thermospheric hydrogen density prior to severe storm of September 8, 2017 and its impact on the storm manifestations

<p>Atomic hydrogen plays a key role for the plasmasphere, exosphere, and the nighttime ionosphere. It directly impacts the rate of plasmasphere refilling after strong magnetic storms as atomic hydrogen is the primary source of hydrogen ions. It is the source of the geocorona, which significantly affects ring current decay during the recovery phase of magnetic storms.</p><p>Our previous studies with the Kharkiv incoherent scatter radar (49.6 N, 36.3 E), Arase and DMSP satellite missions, and FLIP physical model showed that during magnetically quiet periods of 2016–2018 the hydrogen density was generally a factor of 2 higher than from the NRLMSIS00-E model (Kotov et al., 2018).</p><p>Even larger values of thermospheric hydrogen density were detected prior to the severe storm of September 8, 2017. With Kharkiv IS radar, AWDANet whistler receivers, Arase satellite, and TEC data we found that during the nights of September 5 to 6 and September 6 to 7, the thermospheric hydrogen density had to be at least a factor of 4 higher than the values from NRLMSIS00-E model i.e. ~100% higher than expected from our previous studies. We discuss the possible mechanisms that could lead to the increased hydrogen density.</p><p>Such high hydrogen densities may be the reason for very quick recovery of inner plasmasphere after the severe depletion by the storm of September 8, 2017 (Obana et al., 2019).</p><p><strong>References:</strong></p><p>1. Kotov, D. V., Richards, P. G., Truhlík, V., Bogomaz, O. V., Shulha, M. O., Maruyama, N., et al. ( 2018). Coincident observations by the Kharkiv IS radar and ionosonde, DMSP and Arase (ERG) satellites, and FLIP model simulations: Implications for the NRLMSISE‐00 hydrogen density, plasmasphere, and ionosphere. Geophysical Research Letters, 45, 8062– 8071. https://doi.org/10.1029/2018GL079206</p><p>2. Obana, Y., Maruyama, N., Shinbori, A., Hashimoto, K. K., Fedrizzi, M., Nosé, M., et al. (2019). Response of the ionosphere‐plasmasphere coupling to the September 2017 storm: What erodes the plasmasphere so severely? Space Weather, 17, 861–876. https://doi.org/10.1029/2019SW002168</p>