Arthur P. Mizzi

Impact Of Cumulus Initialization on the Spinup of Precipitation Forecasts in the Tropics

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 Donners 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...

Comparison of Global Diabatic Heating Rates from FGGE Level IIIb Analyses with Satellite Radiation Imagery Data

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 com...

A Numerical Study of the Mesoscale Atmospheric Circulation Observed during a Coastal Upwelling Event on 23 August 1972. Part I: Sensitivity Studies

Abstract A numerical model is used to study the effect of an Ocean surface temperature gradient on the mesoscale atmospheric circulation. The model is initialized with atmospheric data from 23 August 1972 over the central Oregon coastal zone. After the initial fields are balanced the model is integrated for 24 h and the results are analyzed and compared with observation. Both our analysis and the observations show the development of a coastal, low-level jet after sunset. An analysis of the mesoscale wind component shows that this jet is related to the sudden change in the top of the boundary layer and the increased thermal stratification after sunset. Turbulent mixing and terrestrial heating are found to overwhelm the inland advection of marine air so that there is no daytime thermal front over the land. After sunset the front moves inland in response to long-wave radiation cooling and stabilization of the lower atmosphere. Our analysis shows that the warm zone to the east of the thermal front and the coo...

Estimates of Tropical Analysis Differences in Daily Values Produced by Two Operational Centers

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 ...

Vertical spectral representation in primitive equation models of the atmosphere

Abstract Attempts to represent the vertical structure in primitive equation models of the atmosphere with the spectral method have been unsuccessful to date. The linear stability analysis of Francis showed that small time steps were required for computational stability near the upper boundary with a vertical spectral method using Laguerre polynomials. Machenhauer and Daley used Legendre polynomials in their vertical spectral representation and found it necessary to use an artificial constraint to force temperature to zero when pressure was zero to control the upper-level horizontal velocities. This ad hoc correction is undesirable, and an analysis that shows such a correction is unnecessary is presented. By formulating the model in terms of velocity and geopotential and then using the hydrostatic equation to calculate temperature from geopotential, temperature is necessarily zero when pressure is zero. This strategy works provided the multiplicative inverse of the first vertical derivative of the vertical...

Use of precipitation data for diabatic initialization to improve the tropical analysis of divergence and moisture

SummaryFirst, we review the present status of diabatic initialization used for numerical weather prediction and conclude that the deficiency of diabatic initialization mostly stems from the shortcoming in evaluating diabatic heating rates accurately, particularly the release of latent heat by cumulus convection. This indicates the need to adjust the initial conditions for physical processes, and Krishnamurti and his colleagues introduced in 1984 the concept of “physical initialization.” Since cumulus convection is most sensitive to input data among many physical processes, the adjustment of atmospheric input data to a prediction model to produce desired initial precipitation rates is referred to as “cumulus initialization.”In this article we describe a general approach to diabatic initialization with a special emphasis on cumulus initialization. We present the results of forecasting experiments with a version of the NCAR Community Climate Model (CCM) to demonstrate the efficacy of a cumulus initialization procedure to ameliorate the spinup problern of precipitation. Finally, we discuss application of the present methodology of cumulus initialization for a stability-dependent mass-flux cumulus parameterization of CCM2 to pave the way to complete the diabatic normal mode initialization package for CCM2. Note that the present cumulus initialization scheme can be used to assimilate into the atmospheric analysis of the tropics the precipitation rates estimated by satellite radiometric imagery data.