Global Water Vapor Estimates from Measurements from Active GPS RO Sensors and Passive Infrared and Microwave Sounders

Water vapor plays an important role in both climate change processes and atmospheric chemistry and photochemistry. Global water vapor vertical profile can be derived from satellite infrared and microwave sounders. However, no single remote sensing technique is capable of completely fulfilling the needs for numerical weather prediction, chemistry, and climate studies in terms of vertical resolution, spatial and temporal coverage, and accuracy. In addition to the passive infrared and microwave sounder observations, the active global positioning system (GPS) radio occultation (RO) technique can also provide all-weather temperature and moisture profiles. In this chapter, we describe the current developments of global water vapor vertical profile and total precipitable water derived from active GPS RO measurements. In addition, we also demonstrate the potential improvement of global water vapor estimates using combined active GPS RO and passive IR/MW particularly from Atmospheric InfraRed Sounder (AIRS) and Advanced Technology Microwave Sounder (ATMS) measurements. Results show that because RO data are very sensitive to water vapor variation in the moisture rich troposphere, the RO data are able to provide extra water vapor information for the combined AIRS/ATMS and RO retrievals in the lower troposphere

Modelling atmospheric wet refractivity profile using ground and space-based global positioning system

Precise measurement of atmospheric water vapour has been very challenging due to some limitations of the conventional meteorological systems. Hence, there is a need for Global Positioning System (GPS) for meteorology or GPS meteorology. Therefore, the ground-based GPS meteorology and the space-based GPS Radio Occultation (GPS RO) techniques have been used. The major challenges of groundbased GPS meteorology approach include the lack of surface meteorological data collocating with the location of the ground-based GPS receivers as well as its inability to profile the atmosphere. Whereas the GPS RO technique has a problem of generating profile for the lower tropospheric region which holds the largest amount of water vapour. This research investigates an approach for estimating wet refractivity profile using GPS data. Three specific objectives were set for the study which was conducted in three phases. The first objective assessed GPS Integrated Water Vapour (GPS IWV) in which GPS IWV from interpolated meteorological data and the applicability of Global Pressure and Temperature (GPT2w) model for GPS meteorology was evaluated. The results revealed that the GPS IWV from Automatic Weather Station (AWS) presents good correlation with the radiosonde IWV, the standard deviation of the biases vary spatially from 3.162kg/m2 to 3.878 kg/m2. The actual influence of the errors of GPT2w meteorological parameters on GPT2w-based GPS IWV lies between 2kg/m2 and 3kg/m2, translating to an average relative accuracy of 1.2%. Meanwhile, the sensitivity of the GPS RO data to equatorial water vapour trend was evaluated to achieve second objective. It was found that the GPS RO IWV is highly comparable with the ground-based GPS IWV, having average bias of 1.8kg/m2. Finally, a methodology for GPS wet refractivity retrieval was developed towards achieving the third objective of this research. The Modified Single Exponential Function (MSEF) model for retrieving wet refractivity profile from ground-based GPS Zenith Wet Delay (ZWD) was realised. The output validation using profile from radiosonde and GPS RO observations showed high correlation in each case. In order to improve the performance of the MSEF model, an approach for integrating the ground-based and the space-based GPS data (GIWRef) was formulated. The GIWRef profile is highly correlated with the GPS RO profile, which showed an average improvement of 41% over the initial MSEF method with average correlation coefficient of 0.99. It can be concluded from the foregoing results of the study that the MSEF and GIWREF concepts developed in this work, presents a potential for augmenting weather forecasting and monitoring water vapour system

Comparison between GNSS ground-based and GPS radio occultation precipitable water observations over ocean-dominated regions

Precipitable water (PW) inferred from GPS (Global Positioning System) radio occultation (RO) and ground-based (GB) Global Navigation Satellite System (GNSS) observations are compared between years 2007 and 2014. As previous studies were mainly performed over continental areas we now focus over ocean-dominated geographical areas. Our analysis is done in order to find out how the reliability level of RO results over oceanic areas compares to land. As RO soundings usually miss some information close to the ground, we also assess different methods to complete the lacking data. We found 47 terrestrial stations that lie in islands small and far away from continental areas where the weather might be governed by the sea conditions. From comparisons of almost 5000 collocated samples, PW from RO and GB exhibit a global mean difference around 1 mm, root-mean-square deviation about 5 mm and a correlation above 0.9. The 2007–2014 timeseries and the monthly mean RO and GB PW were also compared to reanalyses per hemisphere, latitude regions and oceans. In each zone it was found that PW from RO, GB and reanalyses all exhibit in general consistent seasonal qualitative behavior. However, quantitative differences exist between reanalyses on one side and RO and GB on the other side. It is shown that PW from reanalyses lacks reliability in areas where the island topography is poorly represented by them. We also conclude that RO and GB seem to be more sensitive for the detection of features that depart from the regular annual cycle.Fil: Burgos Fonseca, Yuditsabet. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Alexander, Pedro Manfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: de la Torre, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Austral. Facultad de Ingeniería; ArgentinaFil: Hierro, Rodrigo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Austral. Facultad de Ingeniería; ArgentinaFil: Llamedo Soria, Pablo Martin. Universidad Austral. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Calori, Andrea Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ingeniería; Argentin

Evaluation of precipitable water vapor from five reanalysis products with ground-based GNSS observations

At present, the global reliability and accuracy of Precipitable Water Vapor (PWV) from different reanalysis products have not been comprehensively evaluated. In this study, PWV values derived by 268 Global Navigation Satellite Systems (GNSS) stations around the world covering the period from 2016 to 2018 are used to evaluate the accuracies of PWV values from five reanalysis products. The temporal and spatial evolution is not taken into account in this analysis, although the temporal and spatial evolution of atmospheric flows is one of the most important information elements available in numerical weather prediction products. The evaluation results present that five reanalysis products with PWV accuracy from high to low are in the order of the fifth generation of European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA5), ERA-Interim, Japanese 55-year Reanalysis (JRA-55), National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), and NCEP/DOE (Department of Energy) according to root mean square error (RMSE), bias and correlation coefficient. The ERA5 has the smallest RMSE value of 1.84 mm, while NCEP/NCAR and NCEP/DOE have bigger RMSE values of 3.34 mm and 3.51 mm, respectively. The findings demonstrate that ERA5 and two NCEP reanalysis products have the best and worst performance, respectively, among five reanalysis products. The differences in the accuracy of the five reanalysis products are mainly attributed to the differences in the spatial resolution of reanalysis products. There are some large absolute biases greater than 4 mm between GNSS PWV values and the PWV values of five reanalysis products in the southwest of South America and western China due to the limit of terrains and fewer observations. The accuracies of five reanalysis products are compared in different climatic zones. The results indicate that the absolute accuracies of five reanalysis products are highest in the polar regions and lowest in the tropics. Furthermore, the effects of different seasons on the accuracies of five reanalysis products are also analyzed, which indicates that RMSE values of five reanalysis products in summer and in winter are the largest and the smallest in the temperate regions. Evaluation results from five reanalysis products can help us to learn more about the advantages and disadvantages of the five released water vapor products and promote their applications.Peer ReviewedPostprint (published version

An investigation of atmospheric temperature profiles in the Australian region using collocated GPS radio occultation and radiosonde data

GPS radio occultation (RO) has been recognised as an alternative atmospheric upper air observation technique due to its distinct features and technological merits. The CHAllenging Minisatellite Payload (CHAMP) RO satellite and FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) RO constellation together have provided about ten years of high quality global coverage RO atmospheric profiles. This technique is best used for meteorological studies in the difficult-to-access areas such as deserts and oceans. To better understand and use RO data, effective quality assessment using independent radiosonde data and its associated collocation criteria used in tempo-spatial domain are important. This study compares GPS RO retrieved temperature profiles from both CHAMP (between May 2001 and October 2008) and FORMOSAT-3/COSMIC (between July 2006 and December 2009) with radiosonde data from 38 Australian radiosonde stations. The overall results show a good agreement between the two data sets. Different collocation criteria within 3 h and 300 km between the profile pairs have been applied and the impact of these different collocation criteria on the evaluation results is found statistically insignificantly. The CHAMP and FORMOSAT-3/COSMIC temperature profiles have been evaluated at 16 different pressure levels and the differences between GPS RO and radiosonde at different levels of the atmosphere have been studied. The result shows that the mean temperature difference between radiosonde and CHAMP is 0.39 °C (with a standard deviation of 1.20 °C) and the one between radiosonde and FORMOSAT-3/COSMIC is 0.37 °C (with a standard deviation of 1.24 °C). Different collocation criteria have been applied and insignificant differences were identified amongst the results

GEWEX water vapor assessment (G-VAP): final report

Este es un informe dentro del Programa para la Investigación del Clima Mundial (World Climate Research Programme, WCRP) cuya misión es facilitar el análisis y la predicción de la variabilidad de la Tierra para proporcionar un valor añadido a la sociedad a nivel práctica. La WCRP tiene varios proyectos centrales, de los cuales el de Intercambio Global de Energía y Agua (Global Energy and Water Exchanges, GEWEX) es uno de ellos. Este proyecto se centra en estudiar el ciclo hidrológico global y regional, así como sus interacciones a través de la radiación y energía y sus implicaciones en el cambio global. Dentro de GEWEX existe el proyecto de Evaluación del Vapor de Agua (VAP, Water Vapour Assessment) que estudia las medidas de concentraciones de vapor de agua en la atmósfera, sus interacciones radiativas y su repercusión en el cambio climático global.El vapor de agua es, de largo, el gas invernadero más importante que reside en la atmósfera. Es, potencialmente, la causa principal de la amplificación del efecto invernadero causado por emisiones de origen humano (principalmente el CO2). Las medidas precisas de su concentración en la atmósfera son determinantes para cuantificar este efecto de retroalimentación positivo al cambio climático. Actualmente, se está lejos de tener medidas de concentraciones de vapor de agua suficientemente precisas para sacar conclusiones significativas de dicho efecto. El informe del WCRP titulado "GEWEX water vapor assessment. Final Report" detalla el estado actual de las medidas de las concentraciones de vapor de agua en la atmósfera. AEMET ha colaborado en la generación de este informe y tiene a unos de sus miembros, Xavier Calbet, como co-autor de este informe

50 anos de sinergia entre geodésia espacial e meteorologia: do erro no posicionamento GNSS a aplicações de previsão de precipitação de curtíssimo prazo

The neutral atmosphere (or troposphere) causes refraction in radio frequency signals, which results in errors in Global Navigation Satellite Systems (GNSS) measurements. In meteorology, this effect can represent important measurements of the concentration of atmospheric constituents, especially in regions where conventional high-altitude atmospheric sounding (radiosondes) cannot be performed. There are two GNSS techniques used for this. In the first one, GNSS receivers are located on terrestrial stations that provide estimates of the vertically integrated moisture content (Precipitable Water Vapor - PWV). In the second case, receivers are in space platforms, which obtains profiles of atmospheric pressure, temperature and humidity, known as GNSS radio occultation. These measurements have significant potential for nowcasting applications (30 minutes in advance) of extreme precipitation events (>35 mm). This paper presents a review of the state of the art in the synergy between Geodesy and Meteorology for modeling the neutral atmosphere (neutrosphere), its effect on GNSS positioning and in the estimation of atmospheric constituents, and their applications. Furthermore, it offers the improvements and new challenges developed in modeling the delay for high accuracy positioning.A atmosfera neutra (ou troposfera) causa refração nos sinais de radiofrequência, que resulta em erros nas medidas do Global Navigation Satellite Systems (GNSS) empregadas no posicionamento geodésico. Já para a Meteorologia esse efeito pode representar medidas importantes da concentração dos constituintes atmosféricos, principalmente em regiões onde não se pode realizar sondagem atmosférica convencional, por meio de radiossondas acopladas a balões. Duas técnicas GNSS podem ser empregadas para isso. A primeira utiliza receptores em estações terrestres que fornecem estimativas do conteúdo integrado verticalmente de umidade na atmosfera neutra (Precipitable Water Vapor - PWV). A segunda, com receptores localizados em plataformas espaciais, com os quais obtém perfis atmosféricos de pressão, temperatura e umidade, na técnica conhecida como Rádio-ocultação GNSS. Essas medidas têm um potencial significativo para aplicações em previsões de curtíssimo prazo (30 minutos) de eventos extremos de precipitação (>35 mm). O objetivo principal deste artigo é realizar uma revisão do estado da arte da sinergia entre a Geodésia e a Meteorologia na modelagem da atmosfera neutra (neutrosfera), seu efeito no posicionamento GNSS e na estimativa dos constituintes atmosféricos e suas aplicações. Além disso, apresenta os aprimoramentos e novos desafios desenvolvidos na modelagem do atraso para o posicionamento de alta acurácia

The Amazon basin as a moisture source for an Atlantic Walker-type Circulation

The Amazon basin constitutes the most developed rainforest in the world, accounting for 15-20% of the global freshwater input into the oceans. The low level flow over this region is climatologically dominated by the Atlantic anticycslone and the trade winds. This yields an incoming oceanic moist air to the continent from the East, which is forced to lift up over the Andes range at the West. The confluence of the entrance of humidity, heat, evaporation and strong rainfall results in an accumulation of water vapor in this region. There is a statistically significant surplus of humidity over land as compared to over ocean (the largest difference is found during austral summer). This turns the Amazon basin into one of the most important heat sources for the tropical atmosphere, feeding a global pattern like the Atlantic Walker-type circulation, where the ascent stage is not over ocean but over land. The Global Positioning System radio occultation data show to be an excellent tool to observe the accumulated water vapor above the Amazon basin.Fil: Hierro, Rodrigo Federico. Universidad Austral. Facultad de Ingeniería. Laboratorio de Investigación Desarrollo y Transferencia - Comisión de Investigaciones Científicas de la Provincia de Buenos Aires. Laboratorio de Investigación Desarrollo y Transferencia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Llamedo Soria, Pablo Martin. Universidad Austral. Facultad de Ingeniería. Laboratorio de Investigación Desarrollo y Transferencia - Comisión de Investigaciones Científicas de la Provincia de Buenos Aires. Laboratorio de Investigación Desarrollo y Transferencia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: de la Torre, Alejandro. Universidad Austral. Facultad de Ingeniería. Laboratorio de Investigación Desarrollo y Transferencia - Comisión de Investigaciones Científicas de la Provincia de Buenos Aires. Laboratorio de Investigación Desarrollo y Transferencia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alexander, Pedro Manfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin