The AROME-WMED reanalyses of the first special observation period of the Hydrological cycle in the Mediterranean experiment (HyMeX)

To study key processes of the water cycle, two special observation periods (SOPs) of the Hydrological cycle in the Mediterranean experiment (HyMeX) took place during autumn 2012 and winter 2013. The first SOP aimed to study high precipitation systems and flash flooding in the Mediterranean area. The AROME-WMED (western Mediterranean) model (Fourrié et al., 2015) is a dedicated version of the mesoscale Numerical Weather Prediction (NWP) AROME-France model, which covers the western Mediterranean basin providing the HyMeX operational center with daily real-time analyses and forecasts. These products allowed for adequate decision-making for the field campaign observation deployment and the instrument operation. Shortly after the end of the campaign, a first reanalysis with more observations was performed with the first SOP operational software. An ensuing comprehensive second reanalysis of the first SOP, which included field research observations (not assimilated in real time) and some reprocessed observation datasets, was made with AROME-WMED. Moreover, a more recent version of the AROME model was used with updated background error statistics for the assimilation process. This paper depicts the main differences between the real-time version and the benefits brought by HyMeX reanalyses with AROME-WMED. The first reanalysis used 9 % additional data and the second one 24 % more compared to the real-time version. The second reanalysis is found to be closer to observations than the previous AROME-WMED analyses. The second reanalysis forecast errors of surface parameters are reduced up to the 18 and 24 h forecast range. In the middle and upper troposphere, fields are also improved up to the 48 h forecast range when compared to radiosondes. Integrated water vapor comparisons indicate a positive benefit for at least 24 h. Precipitation forecasts are found to be improved with the second reanalysis for a threshold up to 10 mm (24 h)-1. For higher thresholds, the frequency bias is degraded. Finally, improvement brought by the second reanalysis is illustrated with the Intensive Observation Period (IOP8) associated with heavy precipitation over eastern Spain and southern France

Forcing single-column models using high-resolution model simulations

To use single column models (SCMs) as a research tool for parametrisation development and process studies, the SCM must be supplied with realistic initial profiles, forcing fields and boundary conditions. We propose a new technique for deriving these required profiles, motivated by the increase in number and scale of high-resolution convection-permitting simulations. We suggest that these high-resolution simulations be coarse-grained to the required resolution of an SCM, and thereby be used as a proxy for the ‘true’ atmosphere. This paper describes the implementation of such a technique. We test the proposed methodology using high-resolution data from the UK Met Office’s Unified Model (MetUM), with a resolution of 4 km, covering a large tropical domain. This data is coarse grained and used to drive the European Centre for Medium-Range Weather Forecast’s (ECMWF) Integrated Forecasting 26 System (IFS) SCM. The proposed method is evaluated by deriving IFS SCM forcing profiles from a consistent T639 IFS simulation. The SCM simulations track the global model, indicating a consistency between the estimated forcing fields and the ‘true’ dynamical forcing in the global model. We demonstrate the benefits of selecting SCM forcing profiles from across a large-domain, namely robust statistics, and the ability to test the SCM over a range of boundary conditions. We also compare driving the SCM with the coarse-grained datase to driving it using the ECMWF operational analysis. We conclude by highlighting the importance of understanding biases in the high-resolution dataset, and suggest that our approach be used in combination with observationally derived forcing datasets

Verification of NWP Model Analyses and Radiosonde Humidity Data with GPS Precipitable Water Vapor Estimates during AMMA

Abstract This paper assesses the performance of the European Centre for Medium-Range Weather Forecasts-Integrated Forecast System (ECMWF-IFS) operational analysis and NCEP–NCAR reanalyses I and II over West Africa, using precipitable water vapor (PWV) retrievals from a network of ground-based GPS receivers operated during the African Monsoon Multidisciplinary Analysis (AMMA). The model analyses show reasonable agreement with GPS PWV from 5-daily to monthly means. Errors increase at shorter time scales, indicating that these global NWP models have difficulty in handling the diurnal cycle and moist processes at the synoptic scale. The ECMWF-IFS analysis shows better agreement with GPS PWV than do the NCEP–NCAR reanalyses (the RMS error is smaller by a factor of 2). The model changes in ECMWF-IFS were not clearly reflected in the PWV error over the period of study (2005–08). Radiosonde humidity biases are diagnosed compared to GPS PWV. The impacts of these biases are evidenced in all three model analyses at the level of the diurnal cycle. The results point to a dry bias in the ECMWF analysis in 2006 when Vaisala RS80-A soundings were assimilated, and a diurnally varying bias when Vaisala RS92 or Modem M2K2 soundings were assimilated: dry during day and wet during night. The overall bias is offset to wetter values in NCEP–NCAR reanalysis II, but the diurnal variation of the bias is observed too. Radiosonde bias correction is necessary to reduce NWP model analysis humidity biases and improve precipitation forecast skill. The study points to a wet bias in the Vaisala RS92 data at nighttime and suggests that caution be used when establishing a bias correction scheme

A high quality reprocessed GPS integrated water vapour dataset for atmospheric process studies, model evaluation and assimilation

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GPS et vapeur d'eau atmosphérique : Application à la campagne HyMeX pour l'étude du cycle de l'eau en Méditerranée

International audienceLes GNSS (systèmes globaux de positionnement par satellites tels que le GPS), constituent actuellement la technique de positionnement la plus utilisée avec des précisions balayant un éventail allant de quelques mètres jusqu'à quelques millimètres.Pour la détermination précise des coordonnées d'un point donné au voisinage de la Terre, l'analyse des observations GNSS nécessite l'estimation de retards à la propagation affectant la transmission des signaux et liés, entre autres, à la teneur de l'atmosphère en vapeur d'eau. Ces retards constituent une nouvelle quantité permettant la description de l'état de la basse atmosphère ; leur adéquation avec des observations issues d'instruments météorologiques plus classiques est largement confirmée.Dans le cadre de la campagne météorologique HyMeX pour l'étude du cycle de l'eau en Méditerranée, nous nous intéressons à l'analyse de données issues de plus de 1000 stations GPS permanentes européennes. Les retards estimés pour ces stations sont utilisés pour évaluer les mesures issues de techniques classiques (radiosondages) ainsi que les analyses opérationnelles du modèle de prévision métrologiques AROME-WMED de Météo-France. Elles permettent également une description précise de la distribution spatio-temporelle de la vapeur d'eau atmosphérique, en particulier lors de phénomènes de pluie intense.L'objectif de ces travaux est, à terme, l'assimilation de ces données GPS dans une nouvelle analyse du modèle AROME-WMED pour une meilleure modélisation de l'humidité atmosphérique sur le domaine méditerranéen

The West African Monsoon water cycle investigated with a ground-based GPS network (Invited)

International audienceA permanent network of six ground-based GPS receivers was established in five West African countries during the course of the African Monsoon Multidisciplinary Analysis (AMMA) project. Three stations have been in operation since June 2005, and three others since May 2006, and all provide continuous observations at a 30-sec sampling rate. The data are processed operationally with GAMIT software in delayed-mode and are also reprocessed according to improvements of the GAMIT software. One-hourly precipitable water vapour (PWV) estimates have been used in various studies dealing with the atmospheric water cycle. The operational radiosonde network represents a major source of upper air atmospheric measurements which are assimilated into NWP models. They are also often used for atmospheric process studies of boundary layer dynamics, deep convection and synoptic-scale phenomena, and water budget computations. However, radiosondes suffer from humidity and temperature biases which are detrimental to these studies and negatively impact short-range weather forecasts. Contrary to other regions of the world, GPS data are not assimilated over Africa and therefore represent a unique and valuable source of independent observations for evaluating both radiosonde observations and NWP model products. Results from six co-located GPS - radiosonde comparisons are presented which reveal significant biases with some of the radiosonde sensors used during the AMMA in 2006. The impact of these biases on NWP model analyses is highlighted too, though the models also suffer from other deficiencies. West Africa is a core region for the development of Mesoscale Convective Systems (MCSs) that are responsible for most of the monsoonal rainfall. Some of them transform into a significant portion of the tropical Atlantic cyclones. Understanding the lifecycle of MCSs, their interactions with the continental surface and the ocean are major objectives of AMMA. Water budgets have been computed at high temporal resolution with the help of GPS PWV estimates which give insight into the strength of the water cycle and the special role of MCSs within the monsoon system. At larger spatial and temporal scale, GPS PWV estimates also reveal short periods of strong moisture advection associated with pulsations of the Saharan Heat-Low, especially before the monsoon onset, and reveal a marked seasonal cycle

A high quality reprocessed dataset of GPS tropospheric delay and integrated water vapour for process studies and assimilation into atmospheric models during

International audienc

The West African Monsoon water cycle investigated with a ground-based GPS network (Invited)

International audienceA permanent network of six ground-based GPS receivers was established in five West African countries during the course of the African Monsoon Multidisciplinary Analysis (AMMA) project. Three stations have been in operation since June 2005, and three others since May 2006, and all provide continuous observations at a 30-sec sampling rate. The data are processed operationally with GAMIT software in delayed-mode and are also reprocessed according to improvements of the GAMIT software. One-hourly precipitable water vapour (PWV) estimates have been used in various studies dealing with the atmospheric water cycle. The operational radiosonde network represents a major source of upper air atmospheric measurements which are assimilated into NWP models. They are also often used for atmospheric process studies of boundary layer dynamics, deep convection and synoptic-scale phenomena, and water budget computations. However, radiosondes suffer from humidity and temperature biases which are detrimental to these studies and negatively impact short-range weather forecasts. Contrary to other regions of the world, GPS data are not assimilated over Africa and therefore represent a unique and valuable source of independent observations for evaluating both radiosonde observations and NWP model products. Results from six co-located GPS - radiosonde comparisons are presented which reveal significant biases with some of the radiosonde sensors used during the AMMA in 2006. The impact of these biases on NWP model analyses is highlighted too, though the models also suffer from other deficiencies. West Africa is a core region for the development of Mesoscale Convective Systems (MCSs) that are responsible for most of the monsoonal rainfall. Some of them transform into a significant portion of the tropical Atlantic cyclones. Understanding the lifecycle of MCSs, their interactions with the continental surface and the ocean are major objectives of AMMA. Water budgets have been computed at high temporal resolution with the help of GPS PWV estimates which give insight into the strength of the water cycle and the special role of MCSs within the monsoon system. At larger spatial and temporal scale, GPS PWV estimates also reveal short periods of strong moisture advection associated with pulsations of the Saharan Heat-Low, especially before the monsoon onset, and reveal a marked seasonal cycle

Lagrangian dynamics of the mistral during the HyMeX SOP2

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