Impact of horizontal and vertical localization scales on microwave sounder SAPHIR radiance assimilation
05 May 2016-Vol. 9876
TL;DR: In this article, an Artificial Neural Network (ANN) has been used as a surrogate for the forward radiative calculations and the effect of horizontal and vertical localization scales on the assimilation of direct SAPHIR radiances is studied.
Abstract: In the present study, the effect of horizontal and vertical localization scales on the assimilation of direct SAPHIR radiances is studied. An Artificial Neural Network (ANN) has been used as a surrogate for the forward radiative calculations. The training input dataset for ANN consists of vertical layers of atmospheric pressure, temperature, relative humidity and other hydrometeor profiles with 6 channel Brightness Temperatures (BTs) as output. The best neural network architecture has been arrived at, by a neuron independence study. Since vertical localization of radiance data requires weighting functions, a ANN has been trained for this purpose. The radiances were ingested into the NWP using the Ensemble Kalman Filter (EnKF) technique. The horizontal localization has been taken care of, by using a Gaussian localization function centered around the observed coordinates. Similarly, the vertical localization is accomplished by assuming a function which depends on the weighting function of the channel to be assimilated. The effect of both horizontal and vertical localizations has been studied in terms of ensemble spread in the precipitation. Aditionally, improvements in 24 hr forecast from assimilation are also reported.
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01 Jan 2020
TL;DR: The Megha-Tropiques mission has been operating since 12 October 2011 and serves research and operational objectives related to the tropical water and energy cycle as mentioned in this paper, where the satellite is on a low inclination orbit that enhances the sampling over the intertropical belt.
Abstract: The Megha-Tropiques mission is operating since 12 October, 2011 and serves research and operational objectives related to the tropical water and energy cycle. The satellite is on a low inclination orbit that enhances the sampling over the intertropical belt. The original payloads were dedicated to the estimation of the radiation budget at the top of the atmosphere, the water vapor profiles and the instantaneous precipitation rate. The original suite of geophysical products that was developed permitted to demonstrate the proof of concept of the mission in the early part of its operation. Following an unfortunately expedited exploitation of the conically scanning multispectral radiometer (16 months), efforts have been geared to mitigate the loss by extending the use of the 183 GHz sounder towards the precipitation objectives. This induced some delays in the setting of the current set of products that are now being used for research investigations. Despites not being an operational meteorological satellite, the real time capability of the mission has shown its usefulness with a large and growing set of Numerical Weather Prediction centers assimilating the Megha-Tropiques data, in clear and total skies. After 7 years in space, the satellite and operating instruments are in excellent shape and sustain their very good initial performances. The mission has acquired a large and unique set of observations of the tropical water and energy cycle which is only at the beginning of its exploitation.
3 citations
TL;DR: In this article, a local ensemble transform Kalman filter assimilation algorithm is adopted to ingest microwave sounder radiances directly into the ARW-WRF model, and the effect of assimilation is observed to improve the minimum sea-level pressure values, whereas the improvements in the maximum sustainable wind speed are not significant.
Abstract: Ingesting microwave sounder radiances from SAPHIR of Megha–Tropiques has been attempted. A local ensemble transform Kalman filter assimilation algorithm is adopted to ingest radiances directly into the ARW–WRF model. The forward radiative transfer calculations were surrogated with an artificial neural network (ANN) based on the fast radiative transfer model. Raining pixels from the observations were removed using a threshold test on the observed brightness temperatures. Following this, corrections of both scan and air mass biases were accomplished using a predictor-based approach. The bias characteristics of each channel were calculated from ab initio clear-sky profiles from European reanalysis Interim reanalysis data. The vertical localization functions required for the radiance observations were chosen to be similar to the weighting function of the respective channel. The overall performance of the SAPHIR radiance assimilation in terms of the average error over the forecast period showed a positive impact on the cyclone track prediction when compared with the control run and the best track data from the Indian Meteorological Department. The effect of assimilation is observed to improve the minimum sea-level pressure values, whereas the improvements in the maximum sustainable wind speed are not significant. An assimilation experiment was set up to ingest channel-wise radiances independently, and it was concluded that the assimilation of channel 5 radiances results in the least error in the track forecast. The effect of using ensembles generated by initial perturbations in (i) temperature and (ii) both temperature and humidity was studied. The ensembles generated from perturbations in both humidity and temperature resulted in a better 72-h track compared with perturbation of only one of them. The overall performance of the assimilation of all the six channels for both 48- and 72-h forecast lead times showed a considerable improvement against the control run without any assimilation. Furthermore, the results show a degradation of the forecast of cyclone track in the first 24 h. The sensitivity toward channel-wise radiances showed a positive impact on the precipitation forecast when compared with global precipitation mission rainfall estimates. Threat and bias scores were used for quantitative assessment of precipitation, which indicated improvements in skill after assimilating all six channel radiances from SAPHIR. Finally, a sequential assimilation experiment was set up, and the improvements in the analysis fields were computed.
2 citations
References
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TL;DR: In this article, the impact of assimilating radiance observations from the Advanced Microwave Sounding Unit-A (AMSU-A) on forecasts of several tropical cyclones (TCs) was studied using the Weather Research and Forecasting Model (WRF) and a limited-area ensemble Kalman filter (EnKF).
Abstract: The impact of assimilating radiance observations from the Advanced Microwave Sounding Unit-A (AMSU-A) on forecasts of several tropical cyclones (TCs) was studied using the Weather Research and Forecasting Model (WRF) and a limited-area ensemble Kalman filter (EnKF). Analysis/forecast cycling experiments with and without AMSU-A radiance assimilation were performed over the Atlantic Ocean for the period 11 August–13 September 2008, when five named storms formed. For convenience, the radiance forward operators and bias-correction coefficients, along with the majority of quality-control decisions, were computed by a separate, preexisting variational assimilation system. The bias-correction coefficients were obtained from 3-month offline statistics and fixed during the EnKF analysis cycles. The vertical location of each radiance observation, which is required for covariance localization in the EnKF, was taken to be the level at which the AMSU-A channels’ weighting functions peaked.Deterministic 72-h WR...
102 citations
"Impact of horizontal and vertical l..." refers background in this paper
..., ψN ) (5) With mean, A = 1 N A (6) The deviation from the mean can be written as, A′ = A−A (7)...
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TL;DR: In this article, the authors evaluated the ability of Weather Research and Forecasting (WRF) multi-physics ensembles to simulate storm systems known as East Coast Low (ECLs).
Abstract: This study evaluated the ability of Weather Research and Forecasting (WRF) multi-physics ensembles to simulate storm systems known as East Coast Lows (ECLs). ECLs are intense low-pressure systems that develop off the eastern coast of Australia. These systems can cause significant damage to the region. On the other hand, the systems are also beneficial as they generate the majority of high inflow to coastal reservoirs. It is the common interest of both hazard control and water management to correctly capture the ECL features in modeling, in particular, to reproduce the observed spatial rainfall patterns. We simulated eight ECL events using WRF with 36 model configurations, each comprising physics scheme combinations of two planetary boundary layer (pbl), two cumulus (cu), three microphysics (mp), and three radiation (ra) schemes. The performance of each physics scheme combination and the ensembles of multiple physics scheme combinations were evaluated separately. Results show that using the ensemble average gives higher skill than the median performer within the ensemble. More importantly, choosing a composite average of the better performing pbl and cu schemes can substantially improve the representation of high rainfall both spatially and quantitatively.
61 citations
"Impact of horizontal and vertical l..." refers background in this paper
...Re = Υ (Υ ) N − 1 (12) Finally, the standard analysis equation can be written as, A = A+ PeH T (HPeH T +Re) −1(D −HA) (13) In the above equation, H refers to the observation operator which maps the state variables on to the observation space....
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TL;DR: In this paper, the potential of the Advanced Microwave Sounding Unit (AMSU) observations to identify and characterize precipitating systems in the Mediterranean region is explored, where single channels or combination channels from AMSU-A are used to detect and locate upper level potential vorticity anomalies that are often associated with intensification of surface low systems and occurrence of extreme events.
Abstract: The potential of the Advanced Microwave Sounding Unit (AMSU) observations to identify and characterize precipitating systems in the Mediterranean region is explored. Single channels or combination channels from AMSU-A are used to detect and locate upper level potential vorticity anomalies that are often associated with intensification of surface low systems and occurrence of extreme events, while AMSU-B data is used to detect precipitating areas. The motivation for the approach presented here is the direct use of satellite data as an alternative for reanalysis data sets for climatological studies of Mediterranean lows, without relying on retrieval algorithms. AMSU-A channel 8 was found to be more suitable to identify upper level southward intrusions of stratospheric air than the difference of channels 7 and 5, which detects only vertically deep intrusions. A combination of AMSU-B channels 3 and 5 is able to discriminate moderate to strongly precipitating areas with good agreement with Tropical Rainfall Measuring Mission (TRMM) derived products and independent ground-based data. A more stringent condition based on differences of channels 3 to 5 was found to be useful to detect deep convective clouds. We demonstrate the applicability of AMSU to detect upper level features and precipitating systems for selected case studies of extreme precipitation in the Mediterranean region. These tools will allow us to form a climatology of moderate to strongly precipitating systems, and to investigate their relationship with upper level features that may be precursors of extreme events, and to establish a typology of the precipitating systems in the Mediterranean region.
42 citations
TL;DR: In this article, the authors developed a general purpose, polarized, microwave radiative transfer forward model, including calculation of interaction parameters for fast, simultaneous and accurate generation of radiances, for use in a wide variety of atmospheric retrieval applications.
28 citations
"Impact of horizontal and vertical l..." refers methods in this paper
...Pe = A(A) N − 1 (8) The measurements vectors d were added with a white Gaussian noise as shown below in order to have perturbed observations for different ensembles....
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TL;DR: In this article, an initial assessment of the quality of radiances measured from SAPHIR (Sounder for Probing Vertical Profiles of Humidity) on board Megha-Tropiques (Indo-French joint satellite), launched by the Indian Space Research Organisation on 12 October 2011, is presented.
Abstract: [1] This study presents an initial assessment of the quality of radiances measured from SAPHIR (Sounder for Probing Vertical Profiles of Humidity) on board Megha-Tropiques (Indo-French joint satellite), launched by the Indian Space Research Organisation on 12 October 2011. The radiances measured from SAPHIR are compared with those simulated by the radiative transfer model (RTM) using radiosondes measurements, Atmospheric Infrared Sounder retrievals, and National Centers for Environmental Prediction (NCEP) analyzed fields over the Indian subcontinent, during January to November 2012. The radiances from SAPHIR are also compared with the similar measurements available from Microwave Humidity Sounder (MHS) on board MetOp-A and NOAA-18/19 satellites, during January to November 2012. A limited comparison is also carried out between SAPHIR measured and the RTM computed radiances using European Centre for Medium-Range Weather Forecasts analyzed fields, during May and November 2012. The comparison of SAPHIR measured radiances with RTM simulated and MHS observed radiances reveals that SAPHIR observations are of good quality. After the initial assessment of the quality of the SAPHIR radiances, these radiances have been assimilated within the Weather Research and Forecasting (WRF) three-dimensional variational data assimilation system. Analysis/forecast cycling experiments with and without SAPHIR radiances are performed over the Indian region during the entire month of May 2012. The assimilation of SAPHIR radiances shows considerable improvements (with moisture analysis error reduction up to 30%) in the tropospheric analyses and forecast of moisture, temperature, and winds when compared to NCEP analyses and radiances measurement obtained from MHS, Advanced Microwave Sounding Unit-A, and High Resolution Infrared Sounder. Assimilation of SAPHIR radiances also resulted in substantial improvement in the precipitation forecast skill when compared with satellite-derived rain. Overall, initial results show the usefulness of SAPHIR radiances in the numerical weather prediction data assimilation systems.
21 citations