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- Author or Editor: Arthur P. Mizzi x
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Abstract
In order to asses the uncertainty of daily synoptic analyses for the atmospheric state, the intercomparison of three First GARP Global Experiment (FGGE) level IIIb datasets is conducted. The original analyses and reanalyses produced by the European Centre for Medium Range Weather Forecasts (ECMWF) are compared with the reanalyses produced by the National Meteorological Center (NMC) system, operational in early 1987. Daily values of vorticity ζ, divergence δ, temperature T, static stability Γ, mixing ratio q, vertical motion ω, and diagnosed diabatic heating rate are compared for the period of 26 January–11 February 1979. The spatial mean and variance, temporal mean and variance, two-dimensional wavenumber power spectrum, anomaly correlation, and normalized square difference are used for comparison. Also, equivalent blackbody temperatures from the TIROS-N are used as a proxy to the vertical motion and diagnosed diabatic heating rates in the tropics.
Data are interpolated onto the σ coordinates of the NCAR Community Climate Model (CCM 1 ) with 12 vertical levels. Global data are expanded in spherical harmonics with two resolutions [triangular 13 (T 13) and T42] in order to investigate how data agreement changes depending on the horizontal length scale. Other questions to be investigated are: What aspects of the analyses have improved in the FGGE reanalyses produced at the ECMWF and NMC? What aspects of the analyses are still unsatisfactory? What can be done to further improve the analyses? Since data agreement tends to be weak in the tropics, attention is focused in the tropical belt of 30°N–30°S. One enlightening finding is that both ζ and δ of the NMC reanalyses agree more closely with the ECMWF reanalyses than their earlier analyses. This result may indicate that both the data quality and the analysis techniques have improved. More good news is found in that the agreement of ζ at T13 is excellent, while there is only slight disagreement at T42, indicating that FGGE has succeeded in describing the quasi-rotational state of the atmosphere, even in the tropics. The bad news is that interanalysis agreement of δ and q>/ is poor. Similarly, the analyses of ω show the least agreement, indicating the need for further improvement in describing the diabatically driven irrotational circulations of the tropics.
Abstract
In order to asses the uncertainty of daily synoptic analyses for the atmospheric state, the intercomparison of three First GARP Global Experiment (FGGE) level IIIb datasets is conducted. The original analyses and reanalyses produced by the European Centre for Medium Range Weather Forecasts (ECMWF) are compared with the reanalyses produced by the National Meteorological Center (NMC) system, operational in early 1987. Daily values of vorticity ζ, divergence δ, temperature T, static stability Γ, mixing ratio q, vertical motion ω, and diagnosed diabatic heating rate are compared for the period of 26 January–11 February 1979. The spatial mean and variance, temporal mean and variance, two-dimensional wavenumber power spectrum, anomaly correlation, and normalized square difference are used for comparison. Also, equivalent blackbody temperatures from the TIROS-N are used as a proxy to the vertical motion and diagnosed diabatic heating rates in the tropics.
Data are interpolated onto the σ coordinates of the NCAR Community Climate Model (CCM 1 ) with 12 vertical levels. Global data are expanded in spherical harmonics with two resolutions [triangular 13 (T 13) and T42] in order to investigate how data agreement changes depending on the horizontal length scale. Other questions to be investigated are: What aspects of the analyses have improved in the FGGE reanalyses produced at the ECMWF and NMC? What aspects of the analyses are still unsatisfactory? What can be done to further improve the analyses? Since data agreement tends to be weak in the tropics, attention is focused in the tropical belt of 30°N–30°S. One enlightening finding is that both ζ and δ of the NMC reanalyses agree more closely with the ECMWF reanalyses than their earlier analyses. This result may indicate that both the data quality and the analysis techniques have improved. More good news is found in that the agreement of ζ at T13 is excellent, while there is only slight disagreement at T42, indicating that FGGE has succeeded in describing the quasi-rotational state of the atmosphere, even in the tropics. The bad news is that interanalysis agreement of δ and q>/ is poor. Similarly, the analyses of ω show the least agreement, indicating the need for further improvement in describing the diabatically driven irrotational circulations of the tropics.
Abstract
We evaluate the global distribution of diabatic heating rates based on the thermodynamic energy budget using the ECMWF Level IIIb FGGE analyses. We select the two 15-day periods of 27 January to 10 February 1979, during the FGGE Special Observing Period (SOP)-I, and 7–21 June 1979, in the SOP-II. An effort is made to examine the daily variation of tropospheric diabatic heating in contrast with previous investigations which dealt with the climatological aspect. The daily variations of tropospheric diabatic heating appear to be related to synoptic features of the global circulation, indicating that the diagnosed heating distributions provide useful information related to numerical weather prediction. Nevertheless, a question may be raised regarding the accuracy of the daily variations of diagnosed heating rates, since the calculation of diabatic heating involves an observationally sensitive quantity, i.e., the vertical motion.
One way to investigate the accuracy of diagnosed heating rates is to compare the present results with similar calculating using different FGGE datasets. In the Appendix, we present the diagnosed heating rats based on the GFDL Level IIIb data for the SOP-I study period. While comparisons of heating rates calculated from different analyses are revealing, we still lack an independent measure of comparison. We propose, therefore, the use of infrared and visible radiometric imagery data from the TIROS-N to examine the reliability of diagnosed heating and vertical velocity distributions in the tropics. A stratification of radiance data in terms of cloud types helps to establish useful relationships between infrared radiance and diabatic heating (and vertical velocity), suggesting that radiance data may be used to infer the distribution of diabatic heating in the tropics and to improve the analysis of the divergent wind field.
Abstract
We evaluate the global distribution of diabatic heating rates based on the thermodynamic energy budget using the ECMWF Level IIIb FGGE analyses. We select the two 15-day periods of 27 January to 10 February 1979, during the FGGE Special Observing Period (SOP)-I, and 7–21 June 1979, in the SOP-II. An effort is made to examine the daily variation of tropospheric diabatic heating in contrast with previous investigations which dealt with the climatological aspect. The daily variations of tropospheric diabatic heating appear to be related to synoptic features of the global circulation, indicating that the diagnosed heating distributions provide useful information related to numerical weather prediction. Nevertheless, a question may be raised regarding the accuracy of the daily variations of diagnosed heating rates, since the calculation of diabatic heating involves an observationally sensitive quantity, i.e., the vertical motion.
One way to investigate the accuracy of diagnosed heating rates is to compare the present results with similar calculating using different FGGE datasets. In the Appendix, we present the diagnosed heating rats based on the GFDL Level IIIb data for the SOP-I study period. While comparisons of heating rates calculated from different analyses are revealing, we still lack an independent measure of comparison. We propose, therefore, the use of infrared and visible radiometric imagery data from the TIROS-N to examine the reliability of diagnosed heating and vertical velocity distributions in the tropics. A stratification of radiance data in terms of cloud types helps to establish useful relationships between infrared radiance and diabatic heating (and vertical velocity), suggesting that radiance data may be used to infer the distribution of diabatic heating in the tropics and to improve the analysis of the divergent wind field.
Abstract
In order to ameliorate the precipitation spinup problem (prediction models’ inability to produce realistic precipitation rates at the beginning of the forecast period), the impact of a tropical initialization procedure on precipitation forecasts has been investigated. The procedure is divided into the three components. 1) application of diabatic nonlinear normal-mode initialization (NNMI), 2) modification of the initial divergence by incorporation of satellite-imagery data, and 3) modification of the moisture and temperature fields by Donner's cumulus-initialization scheme. Numerical experiments were conducted by running 10.5-h forecasts (42 time steps) starting from various initial conditions after application of some combination of the three initialization components. A triangular-42 version of the National Center for Atmospheric Research (NCAR) Community Climate Model-1 global spectral model (CCM1) and its associated NNMI package were used. The results of a case study from the reanalyzed First GARP (Global Atmospheric Research Program) Global Experiment (FGGE) level III data show that 1) even if a good estimate of diabatic heating rates were available, diabatic NNMI alone would not solve the spinup problem, 2) the adjustments of moisture and temperature using the cumulus initialization are essential to ameliorate the spinup problem, and 3) the divergence adjustment, assisted by satellite-imagery data, is beneficial when used in conjunction with the cumulus initialization and diabatic NNMI procedures.
Abstract
In order to ameliorate the precipitation spinup problem (prediction models’ inability to produce realistic precipitation rates at the beginning of the forecast period), the impact of a tropical initialization procedure on precipitation forecasts has been investigated. The procedure is divided into the three components. 1) application of diabatic nonlinear normal-mode initialization (NNMI), 2) modification of the initial divergence by incorporation of satellite-imagery data, and 3) modification of the moisture and temperature fields by Donner's cumulus-initialization scheme. Numerical experiments were conducted by running 10.5-h forecasts (42 time steps) starting from various initial conditions after application of some combination of the three initialization components. A triangular-42 version of the National Center for Atmospheric Research (NCAR) Community Climate Model-1 global spectral model (CCM1) and its associated NNMI package were used. The results of a case study from the reanalyzed First GARP (Global Atmospheric Research Program) Global Experiment (FGGE) level III data show that 1) even if a good estimate of diabatic heating rates were available, diabatic NNMI alone would not solve the spinup problem, 2) the adjustments of moisture and temperature using the cumulus initialization are essential to ameliorate the spinup problem, and 3) the divergence adjustment, assisted by satellite-imagery data, is beneficial when used in conjunction with the cumulus initialization and diabatic NNMI procedures.
