scholarly journals On the improvement of wave and storm surge hindcasts by downscaled atmospheric forcing: application to historical storms

2018 ◽  
Vol 18 (4) ◽  
pp. 997-1012 ◽  
Author(s):  
Émilie Bresson ◽  
Philippe Arbogast ◽  
Lotfi Aouf ◽  
Denis Paradis ◽  
Anna Kortcheva ◽  
...  
Keyword(s):  
Storm Surge ◽  
Initial Conditions ◽  
Storm Surges ◽  
Atmospheric Model ◽  
Small Scale ◽  
Severe Damage ◽  
Weather Forecasts ◽  
Whole Process ◽  
Medium Range ◽  
Using Data

Abstract. Winds, waves and storm surges can inflict severe damage in coastal areas. In order to improve preparedness for such events, a better understanding of storm-induced coastal flooding episodes is necessary. To this end, this paper highlights the use of atmospheric downscaling techniques in order to improve wave and storm surge hindcasts. The downscaling techniques used here are based on existing European Centre for Medium-Range Weather Forecasts reanalyses (ERA-20C, ERA-40 and ERA-Interim). The results show that the 10 km resolution data forcing provided by a downscaled atmospheric model gives a better wave and surge hindcast compared to using data directly from the reanalysis. Furthermore, the analysis of the most extreme mid-latitude cyclones indicates that a four-dimensional blending approach improves the whole process, as it assimilates more small-scale processes in the initial conditions. Our approach has been successfully applied to ERA-20C (the 20th century reanalysis).

scholarly journals On the improvement of waves and storm surge hindcasts by downscaled atmospheric forcing: Application to historical storms

2017 ◽  
Author(s):  
Émilie Bresson ◽  
Philippe Arbogast ◽  
Lotfi Aouf ◽  
Denis Paradis ◽  
Anna Kortcheva ◽  
...  
Keyword(s):  
Storm Surge ◽  
Initial Conditions ◽  
Numerical Models ◽  
Storm Surges ◽  
Atmospheric Model ◽  
Coastal Areas ◽  
Wind Forcing ◽  
Small Scale ◽  
Whole Process ◽  
The Impact

Abstract. Winds, waves and storm surges can induce severe damages in coastal areas. The FP7 IncREO project aims to understand the impact of climate change on coastal areas and also to assess the predictability of such extreme events. Reproduce efficiently past events is the fisrt step to reach this purpose. This paper shows the use of atmospheric downscaling techniques in order to improve waves and storm surge hindcasts. Past storms which caused damages on European coastal areas are investigated using atmosphere, wave and storm surge numerical models and downscaling techniques are based on existing ECMWF reanalyses. The results show clearly that the 10 km resolution wind forcing provided by the downscaled atmospheric model gives better waves and surges hindcast against using wind from the reanalysis. Furthermore, the analysis of the most extreme mid-latitude cyclones indicates that a 4D blending approach improves the whole process as it includes small scale processes in the initial conditions.

scholarly journals Turbulent vertical diffusivity in the sub-tropical stratosphere

2007 ◽  
Vol 7 (3) ◽  
pp. 6603-6629 ◽  
Author(s):  
I. Pisso ◽  
B. Legras
Keyword(s):  
Transport Model ◽  
Numerical Models ◽  
Small Scale ◽  
Chemistry Transport Model ◽  
Weather Forecasts ◽  
Chemical Tracers ◽  
Vertical Diffusivity ◽  
Large Ensembles ◽  
Local Equivalent ◽  
Using Data

Abstract. Vertical (cross-isentropic) mixing is produced by small-scale turbulent processes which are still poorly understood and parametrized in numerical models. In this work we provide estimates of local equivalent diffusion in the lower stratosphere by comparing balloon borne high-resolution measurements of chemical tracers with reconstructed mixing ratio from large ensembles of random Lagrangian backward trajectories using European Center for Medium-range Weather Forecasts analysed winds and a chemistry-transport model (REPROBUS). We have investigated cases in subtropical latitudes using data from HIBISCUS campaign. Upper bound on the vertical diffusivity is found to be of the order of 0.5 m2 s−1 in the subtropical region, which is larger than the estimates at higher latitudes. The relation between diffusion and dispersion is studied by estimating Lyapunov exponents and studying their variation according to the presence of active dynamical structures.

scholarly journals What Is the Predictability Limit of Midlatitude Weather?

2019 ◽  
Vol 76 (4) ◽  
pp. 1077-1091 ◽  
Author(s):  
Fuqing Zhang ◽  
Y. Qiang Sun ◽  
Linus Magnusson ◽  
Roberto Buizza ◽  
Shian-Jiann Lin ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Weather Prediction ◽  
Forecast Model ◽  
Small Scale ◽  
Lead Times ◽  
Winter Storms ◽  
Weather Forecasts ◽  
Numerical Weather ◽  
Forecast Lead Time ◽  
Order Of Magnitude

Abstract Understanding the predictability limit of day-to-day weather phenomena such as midlatitude winter storms and summer monsoonal rainstorms is crucial to numerical weather prediction (NWP). This predictability limit is studied using unprecedented high-resolution global models with ensemble experiments of the European Centre for Medium-Range Weather Forecasts (ECMWF; 9-km operational model) and identical-twin experiments of the U.S. Next-Generation Global Prediction System (NGGPS; 3 km). Results suggest that the predictability limit for midlatitude weather may indeed exist and is intrinsic to the underlying dynamical system and instabilities even if the forecast model and the initial conditions are nearly perfect. Currently, a skillful forecast lead time of midlatitude instantaneous weather is around 10 days, which serves as the practical predictability limit. Reducing the current-day initial-condition uncertainty by an order of magnitude extends the deterministic forecast lead times of day-to-day weather by up to 5 days, with much less scope for improving prediction of small-scale phenomena like thunderstorms. Achieving this additional predictability limit can have enormous socioeconomic benefits but requires coordinated efforts by the entire community to design better numerical weather models, to improve observations, and to make better use of observations with advanced data assimilation and computing techniques.

scholarly journals Turbulent vertical diffusivity in the sub-tropical stratosphere

2008 ◽  
Vol 8 (3) ◽  
pp. 697-707 ◽  
Author(s):  
I. Pisso ◽  
B. Legras
Keyword(s):  
Transport Model ◽  
Numerical Models ◽  
Small Scale ◽  
Weather Forecasts ◽  
Chemical Tracers ◽  
Vertical Diffusivity ◽  
Large Ensembles ◽  
Local Equivalent ◽  
Using Data

Abstract. Vertical (cross-isentropic) mixing is produced by small-scale turbulent processes which are still poorly understood and paramaterized in numerical models. In this work we provide estimates of local equivalent diffusion in the lower stratosphere by comparing balloon borne high-resolution measurements of chemical tracers with reconstructed mixing ratio from large ensembles of random Lagrangian backward trajectories using European Centre for Medium-range Weather Forecasts analysed winds and a chemistry-transport model (REPROBUS). We focus on a case study in subtropical latitudes using data from HIBISCUS campaign. An upper bound on the vertical diffusivity is found in this case study to be of the order of 0.5 m2 s−1 in the subtropical region, which is larger than the estimates at higher latitudes. The relation between diffusion and dispersion is studied by estimating Lyapunov exponents and studying their variation according to the presence of active dynamical structures.

THE ECMWF MULTI-TASKING WEATHER PREDICTION MODEL

1991 ◽  
Vol 02 (01) ◽  
pp. 158-186 ◽  
Author(s):  
A.J. SIMMONS ◽  
D. DENT
Keyword(s):  
Weather Prediction ◽  
Atmospheric Model ◽  
Horizontal Resolution ◽  
General Introduction ◽  
Weather Forecasts ◽  
Operational Forecasting ◽  
Medium Range ◽  
Computational Aspects ◽  
Forecasting System ◽  
And Performance

A general introduction to numerical weather prediction is given. The development of the operational forecasting system of the European Centre for Medium-Range Weather Forecasts is summarized, and some results are presented illustrating sensitivity to the horizontal resolution of the atmospheric model, the factor which is most significant in determining computational needs. The spectral method used for the horizontal discretization is described, and computational aspects of its implementation on CRAY-1 and CRAY X-MP machines are discussed. The organization of the multi-tasking employed in the model is presented, and performance figures are given. There is a brief concluding discussion of some likely future developments in medium-range weather prediction.

scholarly journals On the accuracy of analysed low temperatures in the stratosphere

2003 ◽  
Vol 3 (5) ◽  
pp. 1759-1768 ◽  
Author(s):  
B. M. Knudsen
Keyword(s):  
Nitric Acid ◽  
Low Temperatures ◽  
Small Scale ◽  
Cold Bias ◽  
Temperature Variations ◽  
Weather Forecasts ◽  
Scale Temperature ◽  
Medium Range ◽  
Lee Waves ◽  
Stratospheric Clouds

Abstract. The accuracy of ECMWF (European Centre for Medium-Range Weather Forecasts) temperatures has been investigated by comparison to radiosonde temperatures. Particularly, the extent of temperatures below which Polar Stratospheric Clouds (PSCs) consisting of nitric acid trihydrate can exist (TNAT) has been studied. In the 1999/2000 winter analyses and in the 40 year reanalyses (ERA40) from the winter 1996/1997 the analysed extent agrees quite well with the radiosondes extent, whereas the 2002/2003 winter analyses considerably overestimate the extent from 40-11 hPa due to a general cold bias. Close to the frost point small-scale temperature variations, which ECMWF does not catch, substantially increase the extent of these low temperatures. Some of these small-scale variations are caused by lee-waves.

scholarly journals Temporal variability of accumulation at Neumayer station, Antarctica, from stake array measurements and a regional atmospheric model

2002 ◽  
Vol 48 (160) ◽  
pp. 87-94 ◽  
Author(s):  
Elisabeth Schlosser ◽  
Nicole van Lipzig ◽  
Hans Oerter
Keyword(s):  
Climate Model ◽  
Analysis Data ◽  
Atmospheric Model ◽  
Temporal Variations ◽  
Weather Forecasts ◽  
Array Measurements ◽  
Regional Atmospheric Model ◽  
Medium Range ◽  
Measuring Site ◽  
Regional Atmospheric Climate Model

AbstractIn this study we investigate the ability of the Regional Atmospheric Climate MOdel (RACMO) to represent temporal variations of Antarctic accumulation using weekly stake array measurements from Neumayer Station. The model uses European Centre for Medium-Range Weather Forecasts re-analysis data to force the atmospheric variables at the lateral boundaries of the model domain. Accumulation is defined as precipitation minus sublimation. Generally the model represents reasonably well the synoptic situations that lead to precipitation. The amounts of accumulation are, however, usually lower in the model than in the measurements. It cannot be determined whether the model underestimates precipitation or whether this effect is due to the redistribution of snow by the wind, which is not taken into account in the model but affects the accumulation at the measuring site. Significant differences between model and measurements also occur in cases of net ablation due to wind erosion or when accumulation at the stakes was due to snowdrift from the southwest without precipitation being observed.

scholarly journals Preliminary signs of the initiation of deep convection by GNSS

2012 ◽  
Vol 12 (8) ◽  
pp. 20351-20382
Author(s):  
H. Brenot ◽  
J. Neméghaire ◽  
L. Delobbe ◽  
N. Clerbaux ◽  
M. Van Roozendael
Keyword(s):  
Deep Convection ◽  
Critical Role ◽  
Small Scale ◽  
Convective System ◽  
Weather Forecasts ◽  
Convective Systems ◽  
Infrared Radiance ◽  
Using Data ◽  
Convective Cells

Abstract. This study reports on the exploitation of GNSS for weather forecasts, especially for nowcasting. We focus on GPS observations (post-processing with a time resolution of 15 min) and try to establish typical configurations of the humidity field which characterise convective systems and particularly which supply forerunners of their initiation associated with deep convection. We show the critical role of GNSS horizontal gradients of humidity to detect small scale structures of the troposphere (i.e. convective cells), and then we present our strategy to obtain typical water vapour configurations by GNSS, called "H2O alert". These alerts are based on a dry/wet contrast taking place during a 30 min window before initiation of a convective system. GNSS observations have been assessed for the rainfall event of the 28–29 June 2005 using data from the Belgian dense network (baseline from 5 to 30 km). To validate our GNSS H2O alert, we use the detection of precipitation by C-band weather radar and thermal infrared radiance of the 10.8-μm channel [Ch09] of SEVIRI instrument on METEOSAT Second Generation. Our H2O alert obtains a score of about 80%.

Optimal Noise Filtering for the Ionospheric Correction of GPS Radio Occultation Signals

2009 ◽  
Vol 26 (7) ◽  
pp. 1398-1403 ◽  
Author(s):  
S. Sokolovskiy ◽  
W. Schreiner ◽  
C. Rocken ◽  
D. Hunt
Keyword(s):  
Radio Occultation ◽  
Residual Effects ◽  
Small Scale ◽  
Neutral Atmosphere ◽  
Simple Method ◽  
Ionospheric Correction ◽  
Weather Forecasts ◽  
Gps Radio Occultation ◽  
Medium Range ◽  
L1 And L2

Abstract GPS radio occultation remote sensing of the neutral atmosphere requires ionospheric correction of L1 and L2 signals. The ionosphere-corrected variables derived from radio occultation signals—such as the phase, Doppler, and bending angle—are affected by small-scale ionospheric effects that are not completely eliminated by the ionospheric correction. They are also affected by noise from mainly the L2 signal. This paper introduces a simple method for optimal filtering of the L4 = L1 − L2 signal used to correct the L1 signal, which minimizes the combined effects of both the small-scale ionospheric residual effects and L2 noise on the ionosphere-corrected variables. Statistical comparisons to high-resolution numerical weather models from the European Centre for Medium-Range Weather Forecasts (ECMWF) validate that this increases the accuracy of radio occultation inversions in the stratosphere.

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