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Microwave Sounding Unit (microwave + sounding_unit)
Kinds of Microwave Sounding Unit Selected AbstractsRadiosonde temperature trends and their uncertainties over eastern China,INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2008Yanjun Guo Abstract Trends and uncertainty in radiosonde temperature records for six sample stations in eastern China are assessed. Results from a complex approach using metadata and a two-phase regression (M-TPR) to capture known and unknown metadata events respectively are compared with an ensemble of possible solutions generated by the Met Office automated homogenization system (QUARC). Independent satellite records from the Microwave Sounding Unit (MSU) record are used to validate breakpoints over the satellite era. Differences in the treatment of metadata and the strictness of the statistical breakpoint detection methods used lead to relatively poor agreement in breakpoint identification. Agreement in long-term (1958,2003) trends in the homogenized data was found to result from a fortuitous cancellation of large differences in the pre- and post-satellite era trends between the two approaches. A consideration of independent MSU satellite data lends some credence to the presence and calculated magnitude of many of the assigned breakpoints that were not associated with recorded metadata events, in the later part of the record. However, it also highlights that neither of the approaches is likely to be perfect at identifying breaks. Improved metadata are likely to prove vital in confirming the presence of these breaks and hence the veracity of the various homogenization approaches to data for eastern China. Copyright © 2007 Royal Meteorological Society [source] Patterns of variability in the satellite microwave sounding unit temperature record: comparison with surface and reanalysis dataINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2003Giovanni Sturaro Abstract Principal component analysis is applied to global temperature records to study the differences in the patterns of variability between surface and troposphere. Surface, Microwave Sounding Unit (lower troposphere, channel 2 and channel 4) and National Centers for Environmental Prediction,National Center for Atmospheric Research reanalysis thickness data are studied in the common period 1979,2000. The patterns of variability are classified into geographical regions and compared. The series of their time coefficients are correlated to assess the existence of common and significant climate-change signals in the form of climatic trends. The objective is to identify the physical processes determining the records' variations and the differences between the surface and the satellite records that might be related to the discrepancy in their globally averaged trend. Major differences were found in the Tropics, where the surface warming is not paralleled in any other record. The surface record has two major patterns over the Tropics, one of which is connected to El Niño,southern oscillation. Satellite variability is instead described by only one pattern, most probably deriving from the merging of the two distinct patterns found for the near-surface records. In the eastern Antarctic a higher troposphere and lower stratosphere negative trend is found connected to ozone depletion. This signal prevails in the satellite record, despite evidence that it is confined only above 500 hPa. A pattern over Siberia is linked to the ,Euro-Siberian oscillation', i.e. the change in the pressure field determining the tracks of the Atlantic storms over the area Copyright © 2003 Royal Meteorological Society [source] The spatial and temporal behaviour of the lower stratospheric temperature over the Southern Hemisphere: the MSU view.INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2001Part I: data, methodology, temporal behaviour Abstract The lower stratosphere monthly temperature anomalies over the Southern Hemisphere derived from soundings made by the Microwave Sounding Unit (MSU) between 1979 and 1997 are analysed. Specifically MSU channel 4 temperature retrievals are considered. Principal component (PC) analysis with the S-mode approach is used in order to isolate grid points that covary in a similar manner and to determine the main features of their temporal behaviour. The first six PCs explain 81.3% of the variance and represent the different time variability patterns observed over the Southern Hemisphere for the ten area clusters determined by the method. The most important feature is common to all the PC score pattern,time series and corresponds to a negative linear trend present in almost all the Southern Hemisphere except over New Zealand and surrounding areas. The negative trend is largest over Antarctica. The remaining features of the temporal variability are different for each PC score and therefore for each cluster region over the Southern Hemisphere. The first PC score pattern shows the impact of the Chichón and Mt Pinatubo eruptions that each produced a 2-year warming over the tropical and sub-tropical lower stratosphere. This variability is orthogonal with the behaviour present over Antarctica. There are different anomalies between 1987 (El Niño) and 1988 (La Niña). This second PC does not show any evidence whatsoever of the volcanic eruptions. The semi-annual wave is present in the anomaly recurrence at mid to high latitudes. Over very low latitudes, close to the Equator, the Quasi-Biennial Oscillation (QBO) band of frequency is also present. Copyright © 2001 Royal Meteorological Society [source] Precipitation analysis using the Advanced Microwave Sounding Unit in support of nowcasting applicationsMETEOROLOGICAL APPLICATIONS, Issue 2 2002Ralf Bennartz We describe a method to remotely sense precipitation and classify its intensity over water, coasts and land surfaces. This method is intended to be used in an operational nowcasting environment. It is based on data obtained from the Advanced Microwave Sounding Unit (AMSU) onboard NOAA-15. Each observation is assigned a probability of belonging to four classes: precipitation-free, risk of precipitation, precipitation between 0.5 and 5 mm/h, and precipitation higher than 5 mm/h. Since the method is designed to work over different surface types, it relies mainly on the scattering signal of precipitation-sized ice particles received at high frequencies. For the calibration and validation of the method we use an eight-month dataset of combined weather radar and AMSU data obtained over the Baltic area. We compare results for the AMSU-B channels at 89 GHz and 150 GHz and find that the high frequency channel at 150 GHz allows for a much better discrimination of different types of precipitation than the 89 GHz channel. While precipitation-free areas, as well as heavily precipitating areas (>5 mm/h), can be identified to high accuracy, the intermediate classes are more ambiguous. This stems from the ambiguity of the passive microwave observations as well as from the non-perfect matching of the different data sources and sub-optimal radar adjustment. In addition to a statistical assessment of the method's accuracy, we present case studies to demonstrate its capabilities to classify different types of precipitation and to work over highly structured, inhomogeneous surfaces. Copyright © 2002 Royal Meteorological Society [source] Estimates of spatial and interchannel observation-error characteristics for current sounder radiances for numerical weather prediction.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 649 2010I: Methods, application to ATOVS data Abstract This is the first part of a two-part article that uses three methods to estimate observation errors and their correlations for clear-sky sounder radiances used in the European Centre for Medium-Range Weather Forecasts (ECMWF) assimilation system. The analysis is based on covariances derived from pairs of first-guess and analysis departures. The methods used are the so-called Hollingsworth/Lönnberg method, a method based on subtracting a scaled version of mapped assumed background errors from first-guess departure covariances and the Desroziers diagnostic. The present article reports the results for the three Advanced TIROS Operational Vertical Sounder (ATOVS) instruments: the Advanced Microwave Sounding Unit (AMSU)-A, High-Resolution Infrared Radiation Sounder (HIRS) and Microwave Humidity Sounder (MHS). The findings suggest that all AMSU-A sounding channels show little or no interchannel or spatial observation-error correlations, except for surface-sensitive channels over land. Estimates for the observation error are mostly close to the instrument noise. In contrast, HIRS temperature-sounding channels exhibit some interchannel error correlations, and these are stronger for surface-sensitive channels. There are also indications for stronger spatial-error correlations for the HIRS short-wave channels. There is good agreement between the estimates from the three methods for temperature-sounding channels. Estimating observation errors for humidity-sounding channels of MHS and HIRS appears more difficult. A considerable proportion of the observation error for humidity-sounding channels appears correlated spatially for short separation distances, as well as between channels. Observation error estimates for humidity channels are generally considerably larger than the instrument noise. Observation error estimates from this study are consistently lower than those assumed in the ECMWF assimilation system. As error correlations are small for AMSU-A, the study suggests that the current use of AMSU-A data in the ECMWF system in terms of observation-error or thinning-scale choices is fairly conservative. Copyright © 2010 Royal Meteorological Society [source] Toward a consistent reanalysis of the upper stratosphere based on radiance measurements from SSU and AMSU-ATHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 645 2009Shinya Kobayashi Abstract Radiance measurements from the Stratospheric Sounding Unit (SSU) and the Advanced Microwave Sounding Unit (AMSU-A) are the primary source of information for stratospheric temperature in reanalyses of the satellite era. To improve the time consistency of the reanalyses, radiance biases need to be properly understood and accounted for in the assimilation system. The investigation of intersatellite differences between SSU and AMSU-A radiance observations shows that these differences are not accurately reproduced by the operational version of the radiative transfer model for the TIROS Operational Vertical Sounder (RTTOV-8). We found that this deficiency in RTTOV was mainly due to the treatment of the Zeeman effect (splitting of the oxygen absorption lines at 60 GHz) and to changes in the spectral response function of the SSU instrument that are not represented in RTTOV. On this basis we present a revised version of RTTOV that can reproduce SSU and AMSU-A intersatellite radiance differences more accurately. Assimilation experiments performed with the revised version of RTTOV in a four-dimensional variational analysis system (4D-Var) show some improvements in the stratospheric temperature analysis. However, significant jumps in the stratospheric temperature analysis still occur when switching satellites, which is due to the fact that systematic errors in the forecast model are only partially constrained by observations. Using a one-dimensional retrieval equation, we show that both the extent and vertical structure of the partial bias corrections must inevitably change when the nature of the radiance measurement changes with the transition from SSU to AMSU-A. Copyright © 2009 Royal Meteorological Society [source] | ||||||||||