Retrieval of water vapor using ground-based observations from a prototype ATOMMS active centimeter- and millimeter-wavelength occultation instrument

A fundamental goal of satellite weather and climate observations is profiling the atmosphere with in situ-like precision and resolution with absolute accuracy and unbiased, all-weather, global coverage. While GPS radio occultation (RO) has perhaps come closest in terms of profiling the gas state from orbit, it does not provide sufficient information to simultaneously profile water vapor and temperature. We have been developing the Active Temperature, Ozone and Moisture Microwave Spectrometer (ATOMMS) RO system that probes the 22 and 183&thinsp;GHz water vapor absorption lines to simultaneously profile temperature and water vapor from the lower troposphere to the mesopause. Using an ATOMMS instrument prototype between two mountaintops, we have demonstrated its ability to penetrate through water vapor, clouds and rain up to optical depths of 17 (7 orders of magnitude reduction in signal power) and still isolate the vapor absorption line spectrum to retrieve water vapor with a random uncertainty of less than 1&thinsp;%. This demonstration represents a key step toward an orbiting ATOMMS system for weather, climate and constraining processes. ATOMMS water vapor retrievals from orbit will not be biased by climatological or first-guess constraints and will be capable of capturing nearly the full range of variability through the atmosphere and around the globe, in both clear and cloudy conditions, and will therefore greatly improve our understanding and analysis of water vapor. This information can be used to improve weather and climate models through constraints on and refinement of processes affecting and affected by water vapor.</p

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

WWRP Polar Prediction Project Implementation Plan for the Year of Polar Prediction (YOPP)

The Year of Polar Prediction (YOPP) is planned for mid-2017 to mid-2019, centred on 2018. Its goal is to enable a significant improvement in environmental prediction capabilities for the polar regions and beyond, by coordinating a period of intensive observing, modelling, prediction, verification, user-engagement and education activities. With a focus on time scales from hours to a season, YOPP is a major initiative of the World Meteorological Organization’s World Weather Research Programme (WWRP) and a key component of the Polar Prediction Project (PPP). YOPP is being planned and coordinated by the PPP Steering Group together with representatives from partners and other initiatives, including the World Climate Research Programme’s Polar Climate Predictability Initiative (PCPI). The objectives of YOPP are to: 1. Improve the existing polar observing system (enhanced coverage, higher-quality observations). 2. Gather additional observations through field programmes aimed at improving understanding of key polar processes. 3. Develop improved representation of key polar processes in (un)coupled models used for prediction. 4. Develop improved (coupled) data assimilation systems accounting for challenges in the polar regions such as sparseness of observational data. 5. Explore the predictability of the atmosphere-cryosphere-ocean system, with a focus on sea ice, on time scales from hours to a season. 6. Improve understanding of linkages between polar regions and lower latitudes, assess skill of models representing these linkages, and determine the impact of improved polar prediction on forecast skill in lower latitudes. 7. Improve verification of polar weather and environmental predictions to obtain better quantitative knowledge on model performance, and on the skill, especially for user- relevant parameters. 8. Identify various stakeholders and establish their decisionmaking needs with respect to weather, climate, ice, and related environmental services. 9. Assess the costs and benefits of using predictive information for a spectrum of users and services. 10. Provide training opportunities to generate a sound knowledge base (and its transfer across generations) on polar prediction related issues. YOPP is implemented in three distinct phases. During the YOPP Preparation Phase (2013 through to mid-2017) this Implementation Plan was developed, which includes key outcomes of consultations with partners at the YOPP Summit in July 2015. Plans will be further developed and refined through focused international workshops. There will be engagement with stakeholders and arrangement of funding, coordination of observations and modelling activities, and preparatory research. During the YOPP Core Phase (mid-2017 to mid-2019), four elements will be staged: intensive observing periods for both hemispheres, a complementary intensive modelling and prediction period, a period of enhanced monitoring of forecast use in decisionmaking including verification, and a special educational effort. Finally, during the YOPP Consolidation Phase (mid-2019 to 2022) the legacy of data, science and publications will be organized. The WWRP-PPP Steering Group provides endorsement throughout the YOPP phases for projects that contribute to YOPP. This process facilitates coordination and enhances visibility, communication, and networking

The potential for observing African weather with GNSS remote sensing

When compared to the wide range of atmospheric sensing techniques, global navigation satellite system (GNSS) offers the advantage of operating under all weather conditions, is continuous, with high temporal and spatial resolution and high accuracy, and has long-term stability. The utilisation of GNSS ground networks of continuous stations for operational weather and climate services is already in place in many nations in Europe, Asia, and America under different initiatives and organisations. In Africa, the situation appears to be different. The focus of this paper is to assess the conditions of the existing and anticipated GNSS reference network in the African region for meteorological applications. The technical issues related to the implementation of near-real-time (NRT) GNSS meteorology are also discussed, including the data and network requirements for meteorological and climate applications. We conclude from this study that the African GNSS network is sparse in the north and central regions of the continent, with a dense network in the south and fairly dense network in the west and east regions of the continent. Most stations lack collocated meteorological sensors and other geodetic observing systems as called for by the GCOS Reference Upper Air Network (GRUAN) GNSS Precipitable Water Task Team and the World Meteorological Organization (WMO). Preliminary results of calculated zenith tropospheric delay (ZTD) from the African GNSS indicate spatial variability and diurnal dependence of ZTD. To improve the density and geometry of the existing network, countries are urged to contribute more stations to the African Geodetic Reference Frame (AFREF) program and a collaborative scheme between different organisations maintaining different GNSS stations on the continent is recommended. The benefit of using spaced based GNSS radio occultation (RO) data for atmospheric sounding is highlighted and filling of geographical gaps from the station-based observation network with GNSS RO is also proposed.University of Pretoria.http://www.hindawi.com/journals/ametehb201

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

Design, Development, and Prelaunch Calibration of a Low Cost 118.75 Ghz Temperature Sounding Radiometer for Cubesat Missions

The 118.75 GHz eight-channel, double-side-band scanning temperature sounding radiometer “MiniRad” for CubeSat missions is intended to serve as a demonstrator for a constellation of low cost, quick turn-around millimeter wave and higher frequency passive sounders and imagers for weather forecasting at high spatial and temporal resolution. This radiometer payload, built at the Center for Environmental Technology in partnership with the Colorado Space Grant Consortium and the National Snow and Ice Data Center at the University of Colorado at Boulder, can provide a 3D temperature map from the earth's surface to an altitude of 18~km. For precise prelaunch antenna calibration, an HE11 mode full wave electromagnetic field analysis was developed in Matlab for determination of an optimal feed horn and offset paraboloidal reflector geometry such that the main beam and spillover efficiencies of the system are maximized, and these and the antenna phase center location that maximizes phase efficiency are precisely known. Results from this analysis were also compared with HFSS and GRASP simulations of the antenna subsystem. The efficacy of employing a 3D-printed corrugated conical horn, operable between 110 and 127 GHz, as the feed for the reflector was addressed due to its very low cost and rapid manufacturability. Horn measurements indicated a reflection coefficient below -15 dB and an 89% average spillover efficiency at the main reflector subtending a 16 degree half-angle. The need for a compact intermediate frequency spectrometer for operation between 50 MHz and 7 GHz resulted in the design and development of an eight-channel lumped element filterbank with bandwidths between 0.25 and 2.2 GHz. Laboratory experiments implemented to characterize the MiniRad helped in achieving radiometer sensitivities close to theoretical limits. Initial performance obtained from airborne measurements over Antarctica during the NASA Operation IceBridge experiment in Oct-Nov 2016 suggested a well-focused scanning antenna subsystem and good separation between the radiometer channels. After final system integration, measurements obtained from prelaunch experiments indicated the antenna 3-dB beamwidth to be broader by ~0.1 degree compared to the idealized simulated pattern, and radiometer sensitivities that agreed to better than 0.5 K with theoretical estimates across all eight channels

Design, Development, and Prelaunch Calibration of a Low Cost 118.75 GHz Temperature Sounding Radiometer for CubeSat Missions

The 118.75 GHz eight-channel, double-side-band scanning temperature sounding radiometer &ldquo;MiniRad&rdquo; for CubeSat missions is intended to serve as a demonstrator for a constellation of low cost, quick turn-around millimeter wave and higher frequency passive sounders and imagers for weather forecasting at high spatial and temporal resolution. This radiometer payload, built at the Center for Environmental Technology in partnership with the Colorado Space Grant Consortium and the National Snow and Ice Data Center at the University of Colorado at Boulder, can provide a 3D temperature map from the earth's surface to an altitude of 18~km. For precise prelaunch antenna calibration, an HE11 mode full wave electromagnetic field analysis was developed in Matlab for determination of an optimal feed horn and offset paraboloidal reflector geometry such that the main beam and spillover efficiencies of the system are maximized, and these and the antenna phase center location that maximizes phase efficiency are precisely known. Results from this analysis were also compared with HFSS and GRASP simulations of the antenna subsystem. The efficacy of employing a 3D-printed corrugated conical horn, operable between 110 and 127 GHz, as the feed for the reflector was addressed due to its very low cost and rapid manufacturability. Horn measurements indicated a reflection coefficient below -15 dB and an 89% average spillover efficiency at the main reflector subtending a 16&deg; half-angle. The need for a compact intermediate frequency spectrometer for operation between 50 MHz and 7 GHz resulted in the design and development of an eight-channel lumped element filterbank with bandwidths between 0.25 and 2.2 GHz. Laboratory experiments implemented to characterize the MiniRad helped in achieving radiometer sensitivities close to theoretical limits. Initial performance obtained from airborne measurements over Antarctica during the NASA Operation IceBridge experiment in Oct-Nov 2016 suggested a well-focused scanning antenna subsystem and good separation between the radiometer channels. After final system integration, measurements obtained from prelaunch experiments indicated the antenna 3-dB beamwidth to be broader by ~0.1&deg; compared to the idealized simulated pattern, and radiometer sensitivities that agreed to better than 0.5 K with theoretical estimates across all eight channels.</p