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Godelieve Deblonde and Stephen English

Abstract

Retrievals using synthetic background fields and observations for the Special Sensor Microwave Imager Sounder (SSMIS) instrument are performed using a one-dimensional variational data assimilation (1DVAR) scheme for clear and cloudy nonprecipitating skies over open oceans. Two retrieval techniques are implemented in the 1DVAR and are extensively tested. Profiles of temperature, marine surface wind speed, and skin temperature are retrieved with both techniques. In addition, with technique A, profiles of the natural logarithm of specific humidity and liquid water path are also retrieved. With technique B, the natural logarithm of total water content (sum of specific humidity and liquid cloud water content) is retrieved instead of the natural logarithm of humidity and liquid water path. A function specifies how total water content is split among its two components. In essence, excess water vapor oversaturation leads to cloud formation. Retrievals in clear and cloudy conditions for a variety of experiments thoroughly demonstrate how technique A works. The choice of humidity control variable, the presence of biases in the moisture retrievals, and the impact of applying a supersaturation constraint are also discussed. Furthermore, in the presence of clouds, it is shown that little temperature information can be extracted with this technique if the a priori cloud vertical distribution is not known well. With technique B, however, temperature information can be extracted from the observations even in the presence of clouds. Because of its more physically based parameterization, it has some skill at positioning the cloud in the vertical direction.

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Stephen J. English

Abstract

Existing use of passive microwave radiances to improve temperature and humidity analyses in the troposphere has been largely restricted to ocean applications. Recent studies have shown that useful information can be extracted from the Special Sensor Microwave Imager (SSM/I), particularly for cloud liquid water and precipitation, over many land and ice surfaces. Furthermore, new work has provided improved estimates of emissivity at frequencies well above those normally used for land surface applications using satellite, airborne, and ground-based methods. In the light of these new developments, information theory was used to investigate the potential for microwave atmospheric temperature and humidity sounding over varied land and ice surfaces using the Advanced Microwave Sounding Unit. It was found that significant information is available even at low altitude over land and sea-ice surfaces. With extensive land areas poorly served by conventional in situ sounding methods, this result gives considerable promise for the enhanced use of satellite sounding data over land. For temperature sounding, the results show that the sensitivity to emissivity depends strongly on the assumptions made about cloud cover. For humidity sounding, and temperature sounding in cloudy areas, an accurate model of emissivity and an accurate a priori estimate of skin temperature are both required to use sounding data effectively.

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Keyi Chen, Stephen English, Niels Bormann, and Jiang Zhu

Abstract

The Fengyun-3 series of satellites (FY-3) began in May 2008 with the launch of FY-3A. The onboard Microwave Humidity Sounders (MWHSs) provide vertical information about water vapor, which is important for numerical weather prediction (NWP). The noise equivalent delta temperature (NEDT) of the MWHS is higher than that of the Microwave Humidity Sounder (MHS) instrument (e.g., on board MetOp-B) but lower than that of the older AMSU-B instruments (on board NOAA-15, NOAA-16, and NOAA-17). Assimilation of MWHS observations into the ECMWF Integrated Forecast System (IFS) improved the fit of short-range forecasts to other observations, notably MHS, and also slightly improved the longer-range forecast scores verified against analyses. Also, assimilating the MWHS on board both FY-3A and FY-3B gave a larger impact than either instrument alone. Furthermore, when MWHS and MHS were added separately to a baseline using neither, the impact of MWHS was found to be comparable to that of MHS. Consequently, ECMWF has been assimilating the FY-3B MWHS data in the operational forecasting system since 24 September 2014. This is the first operational use of Chinese polar-orbiting satellite data by an NWP center outside of China.

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Renato G. Negri, Luiz A. T. Machado, Stephen English, and Mary Forsythe

Abstract

Advances in computer power have made it possible to increase the spatial resolution of regional numerical models to a scale encompassing larger convective elements of less than 5 km in size. One goal of high resolution is to begin to resolve convective processes, and therefore it is necessary to evaluate the realism of convective clouds resolved explicitly at this resolution. This paper presents a method that is based on satellite comparisons to examine the simulation of continental tropical convection over Africa, in a high-resolution integration of the Met Office Unified Model (UK UM), developed under the Cascade project. The spatial resolution of these simulations is 1.5 km, the temporal resolution is 15 min, and the convection is resolved explicitly. The Spinning Enhanced Visible and Infrared Imager (SEVIRI) radiometer measurements were simulated by the Radiative Transfer for the Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder (RTTOV) model, and then a comparison between the simulations and real SEVIRI measurements was performed. The analysis using the presented method shows that the UK UM can represent tropical convection dynamics realistically. However, an error has been found in the high-level humidity distribution, which is characterized by strong humidity gradients. A key point of this paper is to present a method for establishing the credibility of a convection-permitting model by direct comparison with satellite data.

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In-Hyuk Kwon, Stephen English, William Bell, Roland Potthast, Andrew Collard, and Benjamin Ruston
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William Bell, Sabatino Di Michele, Peter Bauer, Tony McNally, Stephen J. English, Nigel Atkinson, Fiona Hilton, and Janet Charlton

Abstract

The sensitivity of NWP forecast accuracy with respect to the radiometric performance of microwave sounders is assessed through a series of observing system experiments at the Met Office and ECMWF. The observing system experiments compare the impact of normal data from a single Advanced Microwave Sounding Unit (AMSU) with that from an AMSU where synthetic noise has been added. The results show a measurable reduction in forecast improvement in the Southern Hemisphere, with improvements reduced by 11% for relatively small increases in radiometric noise [noise-equivalent brightness temperature (NEΔT) increased from 0.1 to 0.2 K for remapped data]. The impact of microwave sounding data is shown to be significantly less than was the case prior to the use of advanced infrared sounder data [Atmospheric Infrared Sounder (AIRS) and Infrared Atmospheric Sounding Interferometer (IASI)], with microwave sounding data now reducing Southern Hemisphere forecast errors by approximately 10% compared to 40% in the pre-AIRS/IASI period.

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Stephen English, Catherine Prigent, Ben Johnson, Simon Yueh, Emmanuel Dinnat, Jacqueline Boutin, Stuart Newman, Magdalena Anguelova, Thomas Meissner, Masahiro Kazumori, Fuzhong Weng, Alexandre Supply, Lise Kilic, Michael Bettenhausen, Ad Stoffelen, and Christophe Accadia
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Robert Palmer, David Whelan, David Bodine, Pierre Kirstetter, Matthew Kumjian, Justin Metcalf, Mark Yeary, Tian-You Yu, Ramesh Rao, John Cho, David Draper, Stephen Durden, Stephen English, Pavlos Kollias, Karen Kosiba, Masakazu Wada, Joshua Wurman, William Blackwell, Howard Bluestein, Scott Collis, Jordan Gerth, Aaron Tuttle, Xuguang Wang, and Dusan Zrnic
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