39 research outputs found

    ON THE ASSIMILATION OF GNSS PWV MEASUREMENTS IN HEAVY TO TORRENTIAL RAIN EVENTS IN DAVAO CITY, PHILIPPINES

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    A standalone Global Navigation Satellite System (GNSS) receiver was utilized in this study to get a measure of the atmospheric water vapor in Davao City, Philippines. It aims to monitor the variability of GNSS precipitable water vapor (PWV) especially during heavy to torrential rain. The results of the study showed a positive correlation between GNSS-PWV and precipitation especially in these severe (heavy to torrential) rain events which implies that the assimilation of atmospheric water vapor measurements can improve forecasts of such events

    Atmospheric Effects and Precursors of Rainfall over the Swiss Plateau

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    In this study, we investigate the characteristics of atmospheric parameters before, during, and after rain events in Bern, Switzerland. Ground-based microwave radiometer data of the TROpospheric WAter RAdiometer (TROWARA) with a time resolution of 7 s, observations of a weather station, and the composite analysis method are used to derive the temporal evolution of rain events and to identify possible rainfall precursors during a 10-year period (1199 available rain events). A rainfall climatology is developed using parameters integrated water vapor (IWV), integrated liquid water (ILW), rain rate, infrared brightness temperature (TIR), temperature, pressure, relative humidity, wind speed, and air density. It was found that the IWV is reduced by about 2.2 mm at the end of rain compared to the beginning. IWV and TIR rapidly increase to a peak at the onset of the rainfall. Precursors of rainfall are that the temperature reaches its maximum around 30 to 60 min before rain, while the pressure and relative humidity are minimal. IWV fluctuates the most before rain (obtained with a 10 min bandpass). In 60% of rain events, the air density decreases 2 to 6 h before the onset of rain. The seasonality and the duration of rain events as well as the diurnal cycle of atmospheric parameters are also considered. Thus, a prediction of rainfall is possible with a true detection rate of 60% by using the air density as a precursor. Further improvements in the nowcasting of rainfall are possible by using a combination of various atmospheric parameters which are monitored by a weather station and a ground-based microwave radiometer

    Analysis of Precipitable Water Vapour in Angola Using GNSS Observations

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    For accurate weather predictions and analysis of extreme events, a good estimate of the amount of water content in the atmosphere is essential. This information is provided by several techniques like radiosondes that measure this parameter at various heights. However, most of them are very limited spatially and temporarily or suffer from measurement specific constraints. To complement these techniques, Precipitable Water Vapor (PWV) can be measured with GNSS (Global Navigation Satellite System) at CORS (Continuously Operating Reference Stations) networks. when the temperature and pressure are also known at the station location. PWV can be derived from the delay in the GNSS signal when it passes through the troposphere. In the framework of SUGGEST-AFRICA, it is being implemented a system to use the national GNSS stations for the automatic computation of PWV in Angola. Thus, this dissertation intends to describe the necessary steps to develop a system to be used for supporting meteorological and climate applications in Angola. SUGGEST-AFRICA also funded the installation of 5 weather stations, collocated with GNSS stations in Angola namely: Benguela, Cabinda, Cuito, Luanda and Namibe, in order to obtain pressure and temperature which is necessary to obtain the PWV estimates. When there are no nearby meteorological stations, the potential alternative is to use values from global/regional models. Methodologies have been optimized to passive and actively access the GNSS data; the PWV estimations are computed using PPP (Precise Point Positioning), which permits the estimation of each station separately; solutions have been validated using internal values. In addition, analyses are presented to evaluate the reliability of the network. This work presents preliminary results for the variation of the ZTD data available all around the territory in Angola and how they relate to the seasonal variations in water vapour. Also, presents preliminary results for the time-series variation of PWV in the Luanda station (collocated by the SEGAL group). This study is supported by SUGGEST-AFRICA, funded by Fundação Aga Khan and FCT. It uses computational resources provided by C4G – Collaboratory for Geosciences (PINFRA/22151/2016). It is also supported by project FCT/UIDB/50019/2020 – IDL funded by FCT.Para precisão da previsão do tempo e análise de eventos extremos é fundamental uma boa estimativa do vapor da água na atmosfera. O vapor da água na atmosfera é fornecido por várias técnicas como radio sondagem que mede este parâmetro em várias alturas. No entanto, muito dessas técnicas são limitadas devido a resolução espacial e temporal ou sofrem restrições específicas de medição. Para completar estas limitações encontrado nas demais técnicas, o vapor da água precipitável (PWV) pode ser medido pelo GNSS (Sistemas de navegação global por satélite) CORS (Rede nacional de estações de referência de operação continua). PWV pode ser obtido a partir do atraso do sinal de GNSS através da troposfera, quando a temperatura e a pressão também são conhecidas derivado da localização duma estação meteorológica. No âmbito da SUGGEST-ÁFRICA, esta ser implementado um sistema de modo a calcular o PWV de uma maneira automática em Angola. Assim, nesta dissertação pretende descrever os passos necessários para desenvolver tal sistema a ser utilizado para apoiar aplicações meteorológicas e climáticas em Angola. SUGGEST-ÁFRICA também financiou a instalação de 5 estações meteorológicas, colocada com estações GNSS em Angola, nomeadamente: Benguela, Cabinda, Cuito, Luanda e Namibe, a fim de obter a pressão e a temperatura necessárias para obter as estimativas PWV. Aconselha-se o uso dos modelos globais/regionais para aquisição de valores de pressão e temperatura quando não existe dados nas estações meteorológicas adjacentes. As metodologias foram otimizadas para o acesso passivo e ativo dos dados GNSS; a estimação do vapor de água precipitável é calculada usando a técnica PPP (Posicionamento do ponto preciso), que permite a determinação de cada estação individualmente e separadamente; as soluções foram validadas usando valor interno. Além disso, são apresentadas análises para avaliar a fiabilidade da rede. Este trabalho, também apresenta resultados preliminares para a variação de todo dados do ZTD disponível em Angola e a forma como se relacionam com as variações sazonais do vapor de água. Também, apresenta variação da série temporal do PWV na estação meteorológica de Luanda (instalado pela SEGAL). Este estudo é suportado pela SUGGEST-ÁFRICA, financiado pela fundação Aga Khan e FCT. Utiliza recurso computacional fornecido pela C4G – Colaboração de Geociências (PINFRA/ 22151/2016). Também é apoiado pelo projecto FCT/UIDB/50019/2020 – IDL financiado pela FCT

    Investigating the relationships between precipitable water vapor estimations and heavy rainfall over the Eastern Pacific Ocean and Ecuadorian regions

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    La lluvia es un fenómeno atmosférico difícil de predecir. Más allá de su importancia en las actividades humanas; existen dificultades teóricas y técnicas que justifican el estudio de la lluvia y la lluvia intensa. Los Modelos Numéricos atmosféricos de Predicción como el Weather Research & Forecasting Model (WRF), son las herramientas que se utilizan para predecir y estudiar su comportamiento, aunque presentan limitaciones al trabajar con lluvias intensas y topografías complejas y empinadas. Recientes investigaciones proponen a la estimación vapor de agua troposférico (Precipitable Water Vapor PWV), como una herramienta que puede ayudar a la predicción y entendimiento de los mecanismos que desencadenan lluvia intensa. Productos satelitales y su derivación indirecta a través del retraso de señales de Sistemas de Posicionamiento Global GNSS, son las principales fuentes actuales de PWV. El presente trabajo estudia la relación entre la lluvia intensa y el PWV satelital sobre el océano, la relación de PWV-GNSS sobre la Costa, Sierra y Oriente del Ecuador; así como con los datos modelados en WRF sobre zonas andinas ecuatoriales. Como principales resultados, se tiene un modelo empírico entre el PWV satelital y los valores máximos de lluvia sobre el océano; además, se identifican períodos de carga y descarga del PWV-GNSS relacionados con el ciclo diurno de la lluvia sobre tierra, y relaciones con los eventos intensos de lluvia; y por último, se encuentran las principales discrepancias entre los datos observados PWV- GNSS y lluvia con datos modelados de WRF sobre zonas de los Andes Ecuatoriales.Among the weather phenomena, rainfall is difficult to forecast, despite the theoretical and technical challenges inherently related to its prediction, its impact in economic and everyday activities, clearly justify its study. Numerical Weather Prediction Models are widely used to predict rainfall, such as the Weather Research & Forecasting Model (WRF), However, they underperform when is set to predict intense events and when working with complex and steep topographies. Recent studies have proposed the estimation of Precipitable Water Vapor PWV, as a tool that can help predict and understand the mechanisms that trigger intense rainfall. PWV is mainly sourced from satellite products and from indirectly measurements which derive it through the delay of the Global Navigation Positioning System (GNSS) signals quite accurately. Thus, the present work studies the relationship between intense rain and satellite sourced PWV over the ocean, the relationship of PWV-GNSS over the Coast, Sierra and Amazon of Ecuador, and the comparison of the PWV-GNSS with the data modeled in WRF. As main results, we point an empirical model between the satellite PWV and the maximum values of rainfall over the ocean. In addition, PWV-GNSS loading and unloading periods related to the diurnal cycle of rainfall over the land, and relationships with intense rain events were identified; and finally, the main discrepancies between the observed PWV-GNSS data and rainfall with WRF modeled data over areas of the Equatorial Andes.0000-0002-4496-73230000-0002-4408-85800000-0002-7205-5786Doctora (PhD) en Recursos HídricosCuenc

    Constructing a precipitable water vapor map from regional GNSS network observations without collocated meteorological data for weather forecasting

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    Surface pressure (Ps) and weighted mean temperature (Tm) are two necessary variables for the accurate retrieval of precipitable water vapor (PWV) from Global Navigation Satellite System (GNSS) zenith total delay (ZTD) estimates. The lack of Ps or Tm information is a concern for those GNSS sites that are not collocated with meteorological sensors. This paper investigates an alternative method of inferring accurate Ps and Tm at the GNSS station using nearby synoptic observations. Ps and Tm obtained at the nearby synoptic sites are interpolated onto the location of the GNSS station by performing both vertical and horizontal adjustments, in which the parameters involved in Ps and Tm calculation are estimated from ERA-Interim reanalysis profiles. In addition, we present a method of constructing high-quality PWV maps through vertical reduction and horizontal interpolation of the retrieved GNSS PWVs. To evaluate the performances of the Ps and Tm retrieval, and the PWV map construction, GNSS data collected from 58 stations of the Hunan GNSS network and synoptic observations from 20 nearby sites in 2015 were processed to extract the PWV so as to subsequently generate the PWV maps. The retrieved Ps and Tm and constructed PWV maps were assessed by the results derived from radiosonde and the ERA-Interim reanalysis. The results show that (1) accuracies of Ps and Tm derived by synoptic interpolation are within the range of 1.7–3.0&thinsp;hPa and 2.5–3.0&thinsp;K, respectively, which are much better than the GPT2w model; (2) the constructed PWV maps have good agreements with radiosonde and ERA-Interim reanalysis data with the overall accuracy being better than 3&thinsp;mm; and (3) PWV maps can well reveal the moisture advection, transportation and convergence during heavy rainfall.</p

    Meteorological applications of precipitable water vapor measurements retrieved by the national GNSS network of China

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    AbstractIn this study, the Global Navigation Satellite System (GNSS) network of China is discussed, which can be used to monitor atmospheric precipitable water vapor (PWV). By the end of 2013, the network had 952 GNSS sites, including 260 belonging to the Crustal Movement Observation Network of China (CMONOC) and 692 belonging to the China Meteorological Administration GNSS network (CMAGN). Additionally, GNSS observation collecting and data processing procedures are presented and PWV data quality control methods are investigated. PWV levels as determined by GNSS and radiosonde are compared. The results show that GNSS estimates are generally in good agreement with measurements of radiosondes and water vapor radiometers (WVR). The PWV retrieved by the national GNSS network is used in weather forecasting, assimilation of data into numerical weather prediction models, the validation of PWV estimates by radiosonde, and plum rain monitoring. The network is also used to monitor the total ionospheric electron content

    Tropospheric Delay in the Neapolitan and Vesuvius Areas (Italy) by Means of a Dense GPS Array: A Contribution for Weather Forecasting and Climate Monitoring

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    Studying the spatiotemporal distribution and motion of water vapour (WV), the most variable greenhouse gas in the troposphere, is pivotal, not only for meteorology and climatology, but for geodesy, too. In fact, WV variability degrades, in an unpredictable way, almost all geodetic observation based on the propagation of electromagnetic signal through the atmosphere. We use data collected on a dense GPS network, designed for the purposes of monitoring the active Neapolitan (Italy) volcanoes, to retrieve the tropospheric delay parameters and precipitable water vapour (PWV). This study has two main targets: (a) the analysis of long datasets (11 years) to extract trends of climatological meaning for the region; (b) studying the main features of the time evolution of the PWV during heavy raining events to gain knowledge on the preparatory stages of highly impacting thunderstorms. For the latter target, both differential and precise point positioning (PPP) techniques are used, and the results are compared and critically discussed. An increasing trend, amounting to about 2 mm/decades, has been recognized in the PWV time series, which is in agreement with the results achieved in previous studies for the Mediterranean area. A clear topographic effect is detected for the Vesuvius volcano sector of the network and a linear relationship between PWV and altitude is quantitatively assessed. This signature must be taken into account in any modelling for the atmospheric correction of geodetic and remote-sensing data (e.g., InSAR). Characteristic temporal evolutions were recognized in the PWV in the targeted thunderstorms (which occurred in 2019 and 2020), i.e., a sharp increase a few hours before the main rain event, followed by a rapid decrease when the thunderstorm vanished. Accounting for such a peculiar trend in the PWV could be useful for setting up possible early warning systems for those areas prone to flash flooding, thus potentially providing a tool for disaster risk reduction

    Estimation of integrated water vapor derived from Global Navigation Satellite System observations over Central-Western Argentina (2015–2018). Validation and usefulness for the understanding of regional precipitation events

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    ARTÍCULO PUBLICADO EN REVISTA EXTERNA. This study assesses the possibility of using Global Navigation Satellite System (GNSS) observations in combination with measurements of surface pressure and temperature to derive Integrated Water Vapor (IWVGNSS) estimates in Central-Western Argentina (CWA), a semi-arid region with complex topography. A significant agreement (coefficient of determination > 0.9) is observed between IWVGNSS and IWV estimates from radiosonde measurements, highlighting the capability of the GNSS stations to provide IWVGNSS estimates for a denser network. The variability of the IWV estimates, the atmospheric pressure and precipitation totals for a case study are compared. The results show that the occurrence of the increase in IWV values (positive IWV anomalies) precedes abundant precipitation over the CWA, in conjunction with the presence of mid-troposphere low-pressure anomalies acting as synoptic forcing. This kind of information provides a more comprehensive picture about the atmospheric processes involved in the development of deep convection, and it can be used for the development of contingency plans in the region. Heavy precipitation events and the difference in timing between positive IWV anomalies, both on-site and for their surroundings, should be considered
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