Sensitivity to observations applied to FASTEX cases

The concept of targeted observations was implemented during field experiments such as FASTEX, NORPEX or WSRP in order to cope with some predictability problems. The techniques of targeting used at that moment (adjoint-based or ensemble transform methods) lead to quite disappointing results: the efficiency of the additional observations deployed over sensitive areas did not turn out to remain consistent from one case to another. The influence of targeted observations on the forecasts could sometimes consist of strong improvements, or sometimes strong degradations. It turns out that the latter failure explains why the concept of optimal sampling arose. The efficiency of adaptive sampling appears to depend on the assimilation scheme that deals with the observations. It is then very useful to integrate the nature of the assimilation algorithm, as well as the deployment of the conventional network of observations (redundancy issues between targeted and conventional network) in the definition of the sensitive pattern to be sampled. Therefore, we chose the tool of the sensitivity to observations to allow us to test such an approach. The sensitivity to targeted observations (that utilizes the adjoint of the linearized NWP model and the adjoint of the assimilation operator) seems to be a suitable tool to obtain an insight into the tricky issue of the optimization of the sampling strategies. To understand better the intrinsic patterns and the influence of the 3D-Var assimilation scheme on the sensitive structures to be sampled, we present here some detailed results on a FASTEX targeting case. We focus on the dropsondes deployed by the Gulfstream IV (jet-aircraft) along its first flight during Intense Observing Period 17 that started on the 17 February 1997. The sensitivity to observation is used as a diagnostic tool for studing targeting from a critical point of view. It is shown that assimilation processes can have an important effect on the classical sensitivity fields, and particularly on their vertical extension. For example, in the studied case, the classical sensitivity fields remain at a lower level than 400 hPa, whereas the sensitivity to observations stretches up to 250 hPa. However, the maximum values can be found at approximately 700 hPa in both sensitivity fields. The studied case shows that the efficiency of observations depends not only on the sensitivity but also on the deviations between the observations and the background field. An example of the use of this diagnosis for comparing the relative efficiency of different kinds of observations is also presented. This work points out that it is very complicated to optimize the efficiency of adaptive observations, and that the assimilation of an entire set of observations (both conventional and adaptive network) needs to be considered

A new approach to sensitivity climatologies: the DTS-MEDEX-2009 campaign

Adaptive observation is an approach to improving the quality of numerical weather forecasts through the optimization of observing networks. It is sometimes referred to as Data Targeting (DT). This approach has been applied to high impact weather during specific field campaigns in the past decade. Adaptive observations may involve various types of observations, including either specific research observing platforms or routine observing platforms employed in an adaptive way. The North-Atlantic TReC 2003 and the EURORISK-PREVIEW 2008 exercises focused on the North-Atlantic and Western Europe areas using mainly routine observing systems. These campaigns also included Mediterranean cases. <br><br> The most recent campaign, DTS-MEDEX-2009, is the first campaign in which the DT method has been used to address exclusively Mediterranean high impact weather events. In this campaign, which is an important stage in the MEDEX development, only operational radiosonde stations and commercial aircraft data (AMDAR) have provided additional observations. Although specific diagnostic studies are needed to assess the impact of the extra-observations on forecast skill and demonstrate the effectiveness of DTS-MEDEX-2009, some preliminary findings can be deduced from a survey of this targeting exercise. <br><br> After a description of the data targeting system and some illustrations of particular cases, this paper attempts some comparisons of additional observation needs (through effectively deployed radio-soundings) with sensitivity climatologies in the Mediterranean. The first step towards a sensitivity climatology for Mediterranean cases of high impact weather is indirectly given by the frequency of extra-soundings launched from the network of radiosonde stations involved in the DTS-MEDEX-2009 campaign

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

Sensitivity to observations applied to FASTEX cases

International audienceThe concept of targeted observations was implemented during field experiments such as FASTEX, NORPEX or WSRP in order to cope with some predictability problems. The techniques of targeting used at that moment (adjoint-based or ensemble transform methods) lead to quite disappointing results: the efficiency of the additional observations deployed over sensitive areas did not turn out to remain consistent from one case to another. The influence of targeted observations on the forecasts could sometimes consist of strong improvements, or sometimes strong degradations. It turns out that the latter failure explains why the concept of optimal sampling arose. The efficiency of adaptive sampling appears to depend on the assimilation scheme that deals with the observations. It is then very useful to integrate the nature of the assimilation algorithm, as well as the deployment of the conventional network of observations (redundancy issues between targeted and conventional network) in the definition of the sensitive pattern to be sampled. Therefore, we chose the tool of the sensitivity to observations to allow us to test such an approach. The sensitivity to targeted observations (that utilizes the adjoint of the linearized NWP model and the adjoint of the assimilation operator) seems to be a suitable tool to obtain an insight into the tricky issue of the optimization of the sampling strategies. To understand better the intrinsic patterns and the influence of the 3D-Var assimilation scheme on the sensitive structures to be sampled, we present here some detailed results on a FASTEX targeting case. We focus on the dropsondes deployed by the Gulfstream IV (jet-aircraft) along its first flight during Intense Observing Period 17 that started on the 17 February 1997. The sensitivity to observation is used as a diagnostic tool for studing targeting from a critical point of view. It is shown that assimilation processes can have an important effect on the classical sensitivity fields, and particularly on their vertical extension. For example, in the studied case, the classical sensitivity fields remain at a lower level than 400 hPa, whereas the sensitivity to observations stretches up to 250 hPa. However, the maximum values can be found at approximately 700 hPa in both sensitivity fields. The studied case shows that the efficiency of observations depends not only on the sensitivity but also on the deviations between the observations and the background field. An example of the use of this diagnosis for comparing the relative efficiency of different kinds of observations is also presented. This work points out that it is very complicated to optimize the efficiency of adaptive observations, and that the assimilation of an entire set of observations (both conventional and adaptive network) needs to be considered

Water vapor observations upstream of two intense rainfall events documented in the framework of HyMeX SOP1

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Adaptive observation with drifting platforms

International audienceThe BAMED (Balloons in the Mediterranean) project aims at developping in-situ drifting observing platforms onboard pressurized balloons to be deployed during HyMeX. HyMeX, known as "Hydrological cycle in the Mediterranean Experiment", is an international, multiscale and multidisciplinary experiment including an observing campaign to start in 2012. The BAMED project is lead by the LMD/IPSL (Laboratoire de Météorologie Dynamique), in collaboration with CNES (Centre National d'Etudes Saptiales) and CNRM (Centre National de Recherche en Météorologie). BAMED is supported by the CNES/TOSCA and INSU/LEFE. Within HyMeX, a special attention is dedicated to the predictability of high impact weather events in the Mediterranean basin. Heavy precipitation and wind storms are typical events to focus on. The deployment of specific observing systems during the campaign to observe phenomena with reduced predictability addresses adaptive observation issue. Consequently, BAMED is three-fold: the project includes balloons technical developments at CNES, trajectory modelling at LMD and adaptive observation at CNRM. The objective is to built an efficient and flexible component of the HyMeX observing system. The CNES develops boundary layer pressurized balloons (BLPBs), which can drift above the sea, collecting data that benefit numerical weather prediction systems. Indeed, the prediction of heavy precipitation events lacks of in-situ measurements in the oceanic boundary layer. However, the balloons will be useful if they drift through some so-called sensitive areas. Moreover the control of the flight of such drifting platforms is very limited at a time and location of the launch of the platform. Because the Mediterranean basin is closed and relatively small compared to atmospheric features, the time spent by BLPBs within the basin is expected to be less than 3 days. The dates and the coastal locations of launching these balloons must be thoroughly selected to allow the balloon to drift into the area of interest and prevent the balloon leaving the basin too quickly. Possible launching sites are evaluated through some trajectography and adaptive observation studies on a selection of typical Mediterranean cases. However, a comprehensive adaptive observation system for the Mediterranean basin shall also monitor the predictability of the upstream flow, at larger scales. The only drifting platform that sample the whole troposphere is the CNES-NCAR driftsonde: a stratospheric balloon-carried gondola drop sondes on demand. Such a platform is thought to be helpful, and to benefit also T-NAWDEX, if deployed above the North Atlantic Ocean. A specific targeting guidance tool for drifting platforms has to be set up. This tool is based on the Kalman Filter Sensitivity (KFS) and coupled with accurate trajectory prediction. The KFS predicts areas where additional observations will most benefit the subsequent forecast, accounting for the assimilation of the routine observations. Monitoring of drifting balloons within an adaptive observation approach is a challenge: new tools, new scales, management of the uncertainties related to the balloons' predicted trajectories and anticipation of the cumulative effect of observations being spread over several assimilation cycles. The adaptive observation aspects of BAMED will be described

Adaptive observation with drifting platforms

International audienceThe BAMED (Balloons in the Mediterranean) project aims at developping in-situ drifting observing platforms onboard pressurized balloons to be deployed during HyMeX. HyMeX, known as "Hydrological cycle in the Mediterranean Experiment", is an international, multiscale and multidisciplinary experiment including an observing campaign to start in 2012. The BAMED project is lead by the LMD/IPSL (Laboratoire de Météorologie Dynamique), in collaboration with CNES (Centre National d'Etudes Saptiales) and CNRM (Centre National de Recherche en Météorologie). BAMED is supported by the CNES/TOSCA and INSU/LEFE. Within HyMeX, a special attention is dedicated to the predictability of high impact weather events in the Mediterranean basin. Heavy precipitation and wind storms are typical events to focus on. The deployment of specific observing systems during the campaign to observe phenomena with reduced predictability addresses adaptive observation issue. Consequently, BAMED is three-fold: the project includes balloons technical developments at CNES, trajectory modelling at LMD and adaptive observation at CNRM. The objective is to built an efficient and flexible component of the HyMeX observing system. The CNES develops boundary layer pressurized balloons (BLPBs), which can drift above the sea, collecting data that benefit numerical weather prediction systems. Indeed, the prediction of heavy precipitation events lacks of in-situ measurements in the oceanic boundary layer. However, the balloons will be useful if they drift through some so-called sensitive areas. Moreover the control of the flight of such drifting platforms is very limited at a time and location of the launch of the platform. Because the Mediterranean basin is closed and relatively small compared to atmospheric features, the time spent by BLPBs within the basin is expected to be less than 3 days. The dates and the coastal locations of launching these balloons must be thoroughly selected to allow the balloon to drift into the area of interest and prevent the balloon leaving the basin too quickly. Possible launching sites are evaluated through some trajectography and adaptive observation studies on a selection of typical Mediterranean cases. However, a comprehensive adaptive observation system for the Mediterranean basin shall also monitor the predictability of the upstream flow, at larger scales. The only drifting platform that sample the whole troposphere is the CNES-NCAR driftsonde: a stratospheric balloon-carried gondola drop sondes on demand. Such a platform is thought to be helpful, and to benefit also T-NAWDEX, if deployed above the North Atlantic Ocean. A specific targeting guidance tool for drifting platforms has to be set up. This tool is based on the Kalman Filter Sensitivity (KFS) and coupled with accurate trajectory prediction. The KFS predicts areas where additional observations will most benefit the subsequent forecast, accounting for the assimilation of the routine observations. Monitoring of drifting balloons within an adaptive observation approach is a challenge: new tools, new scales, management of the uncertainties related to the balloons' predicted trajectories and anticipation of the cumulative effect of observations being spread over several assimilation cycles. The adaptive observation aspects of BAMED will be described

Adaptive observation with drifting platforms

International audienceThe BAMED (Balloons in the Mediterranean) project aims at developping in-situ drifting observing platforms onboard pressurized balloons to be deployed during HyMeX. HyMeX, known as "Hydrological cycle in the Mediterranean Experiment", is an international, multiscale and multidisciplinary experiment including an observing campaign to start in 2012. The BAMED project is lead by the LMD/IPSL (Laboratoire de Météorologie Dynamique), in collaboration with CNES (Centre National d'Etudes Saptiales) and CNRM (Centre National de Recherche en Météorologie). BAMED is supported by the CNES/TOSCA and INSU/LEFE. Within HyMeX, a special attention is dedicated to the predictability of high impact weather events in the Mediterranean basin. Heavy precipitation and wind storms are typical events to focus on. The deployment of specific observing systems during the campaign to observe phenomena with reduced predictability addresses adaptive observation issue. Consequently, BAMED is three-fold: the project includes balloons technical developments at CNES, trajectory modelling at LMD and adaptive observation at CNRM. The objective is to built an efficient and flexible component of the HyMeX observing system. The CNES develops boundary layer pressurized balloons (BLPBs), which can drift above the sea, collecting data that benefit numerical weather prediction systems. Indeed, the prediction of heavy precipitation events lacks of in-situ measurements in the oceanic boundary layer. However, the balloons will be useful if they drift through some so-called sensitive areas. Moreover the control of the flight of such drifting platforms is very limited at a time and location of the launch of the platform. Because the Mediterranean basin is closed and relatively small compared to atmospheric features, the time spent by BLPBs within the basin is expected to be less than 3 days. The dates and the coastal locations of launching these balloons must be thoroughly selected to allow the balloon to drift into the area of interest and prevent the balloon leaving the basin too quickly. Possible launching sites are evaluated through some trajectography and adaptive observation studies on a selection of typical Mediterranean cases. However, a comprehensive adaptive observation system for the Mediterranean basin shall also monitor the predictability of the upstream flow, at larger scales. The only drifting platform that sample the whole troposphere is the CNES-NCAR driftsonde: a stratospheric balloon-carried gondola drop sondes on demand. Such a platform is thought to be helpful, and to benefit also T-NAWDEX, if deployed above the North Atlantic Ocean. A specific targeting guidance tool for drifting platforms has to be set up. This tool is based on the Kalman Filter Sensitivity (KFS) and coupled with accurate trajectory prediction. The KFS predicts areas where additional observations will most benefit the subsequent forecast, accounting for the assimilation of the routine observations. Monitoring of drifting balloons within an adaptive observation approach is a challenge: new tools, new scales, management of the uncertainties related to the balloons' predicted trajectories and anticipation of the cumulative effect of observations being spread over several assimilation cycles. The adaptive observation aspects of BAMED will be described

Lagrangian dynamics of the mistral during the HyMeX SOP2

International audienc

Low-Atmosphere Drifting Balloons: Platforms for Environment Monitoring and Forecast Improvement

International audienceAbstract Balloons are one of the key observing platforms for the atmosphere. Radiosounding is the most commonly used technique and provides over a thousand vertical profiles worldwide every day. These data represent an essential cornerstone of data assimilation for numerical weather prediction systems. Although less common (but equally interesting for the in situ investigation of the atmosphere), drifting boundary layer pressurized balloons (BLPBs) offer rare observational skills. These balloons collect meteorological and/or chemical measurements at isopycnal height as they drift in a quasi-Lagrangian way. The BLPB system presented in this paper was developed by the French Space Agency [Centre National d’Études Spatiales (CNES)] and has been used in field experiments focusing on precipitation in Africa [African Monsoon Multiscale Analysis (AMMA)] and the Mediterranean [Hydrological Cycle in the Mediterranean Experiment (HyMeX)] as well as on air pollution in India [Indian Ocean Experiment (INDOEX)] and the Mediterranean [Transport a Longue Distance et Qualite de l’Air dans le bassin Méditerraneen (TRAQA) and Chemistry–Aerosol Mediterranean Experiment (ChArMeX)]. One important advantage of BLPBs is their capability to explore the lowest layers of the atmosphere above the oceans, areas that remain difficult to access. BLPB had a leading role in a complex adaptive observation system for the forecast of severe precipitation events. These balloons collected data in the marine environment of convective systems, which were assimilated in real time to improve the knowledge of the state of the atmosphere in the numerical prediction models of Météo-France