Direct 4D-Var assimilation of all-sky radiances. Part I: Implementation

Bauer, Péter; Geer, Alan; Lopez, Philippe; Salmond, Deborah

doi:10.1002/qj.659

Cited by 188 publications

(163 citation statements)

References 39 publications

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“…Further details of the all-sky microwave imager assimilation at ECMWF are given by Bauer et al (2010), Geer et al (2010b) and Geer andBauer (2010, 2011). For assimilation, a wide range of quality control measures need to be applied, but a smaller set of restrictions will be applied here: observations are restricted to latitudes equatorward of 60 • ; scenes containing sea ice or coasts are removed; the surface temperature must be higher than 274 K over ocean and 278 K over land to help avoid sea ice and snow cover.…”

Section: Ecmwf Systemmentioning

confidence: 99%

“…When all observations, whether clear, cloudy or precipitating, are assimilated using the same scattering-capable radiative transfer model, this is often referred to as an "all-sky" approach (e.g. Bauer et al, 2010). However, it has been difficult to use cloud-and precipitation-affected microwave observations in situations where atmospheric scattering is most important, such as over land surfaces and in temperature and water vapour sounding channels (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Improved scattering radiative transfer for frozen hydrometeors at microwave frequencies

2014

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Abstract. To simulate passive microwave radiances in allsky conditions requires better knowledge of the scattering properties of frozen hydrometeors. Typically, snow particles are represented as spheres and their scattering properties are calculated using Mie theory, but this is unrealistic and, particularly in deep-convective areas, it produces too much scattering in mid-frequencies (e.g. 30-50 GHz) and too little scattering at high frequencies (e.g. 150-183 GHz). These problems make it hard to assimilate microwave observations in numerical weather prediction (NWP) models, particularly in situations where scattering effects are most important, such as over land surfaces or in moisture sounding channels. Using the discrete dipole approximation to compute scattering properties, more accurate results can be generated by modelling frozen particles as ice rosettes or simplified snowflakes, though hexagonal plates and columns often give worse results than Mie spheres. To objectively decide on the best particle shape (and size distribution) this study uses global forecast departures from an NWP system (e.g. observation minus forecast differences) to indicate the quality of agreement between model and observations. It is easy to improve results in one situation but worsen them in others, so a rigorous method is needed: four different statistics are checked; these statistics are required to stay the same or improve in all channels between 10 GHz and 183 GHz and in all weather situations globally. The optimal choice of snow particle shape and size distribution is better across all frequencies and all weather conditions, giving confidence in its physical realism. Compared to the Mie sphere, most of the systematic error is removed and departure statistics are improved by 10 to 60 %. However, this improvement is achieved with a simple "one-size-fits-all" shape for snow; there is little additional benefit in choosing the particle shape according to the precipitation type. These developments have improved the accuracy of scattering radiative transfer sufficiently that microwave all-sky assimilation is being extended to land surfaces, to higher frequencies and to sounding channels.

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Section: Ecmwf Systemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improved scattering radiative transfer for frozen hydrometeors at microwave frequencies

2014

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“…This two-stage approach has been used operationally for the assimilation of precipitation-related observations (Bauer et al, 2006a,b) at ECMWF from June 2005 until March 2009, when it was replaced by direct 4D-Var assimilation for reasons explained in Bauer et al (2010). Before that, the benefits of such a method had been demonstrated for rain-rate observations by Mahfouf (2000, 2002).…”

Section: Introductionmentioning

confidence: 99%

Experimental 1D + 4D‐Var assimilation of CloudSat observations

Janisková

Lopez

Bauer

2011

Quart J Royal Meteoro Soc

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Observations providing three-dimensional information on clouds from space-borne active instruments on board CloudSat and CALIPSO are already available and new satellites, such as EarthCARE, should appear in the near future. This opens new possibilities for exploring the usefulness of this kind of observation, not only for improving model parametrizations but also for investigating their usage in data assimilation to extract information from the data so as to improve the initial atmospheric state. In this study, a 1D + 4D-Var technique has been selected to study the impact of observations related to clouds on 4D-Var analyses and subsequent forecasts. Using this two-step approach, temperature and specific humidity profiles retrieved from 1D-Var assimilation of CloudSat observations have been included in the 4D-Var system. Several experiments have been run for a couple of selected meteorological situations.

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“…Needless to say, bogusing methods are not the panacea. They should soon be replaced by the possibility of assimilating cloud-affected microwave radiances (Bauer et al 2010) and winds from scatterometers to constrain initial storm structure over data-sparse oceanic regions with no routine aircraft reconnaissance such as the southwest Indian Ocean.…”

Section: Discussionmentioning

confidence: 99%

On the Sensitivity of Tropical Cyclone Intensification under Upper-Level Trough Forcing

Leroux

Plu

Roux

2016

Monthly Weather Review

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This study is part of the efforts undertaken to resolve the ''bad trough/good trough'' issue for tropical cyclone (TC) intensity changes and to improve the prediction of these challenging events. Sensitivity experiments are run at 8-km resolution with vortex bogusing to extend the previous analysis of a real case of TC-trough interaction (Dora in 2007). The initial position and intensity of the TC are modified, leaving the trough unchanged to describe a realistic environment. Simulations are designed to analyze the sensitivity of TC prediction to both the variety of TC-trough configurations and the current uncertainty in model analysis of TC intensity and position.Results show that TC intensification under upper-level forcing is greater for stronger vortices. The timing and geometry of the interaction between the two cyclonic potential vorticity anomalies associated with the cutoff low and the TC also play a major role in storm intensification. The intensification rate increases when the TC (initially located 128 northwest of the trough) is displaced 18 closer. By allowing a gradual deformation and equatorward tilting of the trough, both scenarios foster an extended ''inflow channel'' of cyclonic vorticity at midlevels toward the vortex inner core. Conversely, unfavorable interaction is found for vortices displaced 38 or 48 east or northeast. Variations in environmental forcing relative to the reference simulation illustrate that the relationship between intensity change and the 850-200-hPa wind shear is not systematic and that the 200-hPa divergence, 335-350-K mean potential vorticity, or 200-hPa relative eddy momentum fluxes may be better predictors of TC intensification during TC-trough interactions.

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Direct 4D-Var assimilation of all-sky radiances. Part I: Implementation

Cited by 188 publications

References 39 publications

Improved scattering radiative transfer for frozen hydrometeors at microwave frequencies

Improved scattering radiative transfer for frozen hydrometeors at microwave frequencies

Experimental 1D + 4D‐Var assimilation of CloudSat observations

On the Sensitivity of Tropical Cyclone Intensification under Upper-Level Trough Forcing

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