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- Author or Editor: Jin Huang x
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Abstract
An analysis of the large-scale atmospheric circulation patterns over the South Pacific during part of FGGE SOP-1, 10–27 January 1979, is presented. Results, which are derived from Level III-b analyses produced at ECMWF, are composited for three time periods, based on changing characteristics of the South Pacific Convergence Zone (SPCZ): 0000 GMT 10 January–1200 GMT 18 January, when the SPCZ was a quasistationary persistent feature of the circulation; 0000 GMT 19 January–0000 GMT 24 January, when the SPCZ propagated westward and began to weaken; and 1200 GMT 24 January–1200 GMT 27 January, when it disappeared.
The major findings include 1) the buildup of high pressure in the eastern Pacific coincident with the westward movement of the SPCZ, followed by a rapid buildup of high pressure over the central Pacific and demise of the SPCZ; 2) a trend from middle and upper tropospheric wavelike patterns in wind, temperature and height to more zonally-oriented patterns when the SPCZ disappears; and 3) strong cross-equatorial flow from the SPCZ into the Northern Hemisphere during the first period and strong poleward flow from the SPCZ into middle latitudes during the first two periods.
Abstract
An analysis of the large-scale atmospheric circulation patterns over the South Pacific during part of FGGE SOP-1, 10–27 January 1979, is presented. Results, which are derived from Level III-b analyses produced at ECMWF, are composited for three time periods, based on changing characteristics of the South Pacific Convergence Zone (SPCZ): 0000 GMT 10 January–1200 GMT 18 January, when the SPCZ was a quasistationary persistent feature of the circulation; 0000 GMT 19 January–0000 GMT 24 January, when the SPCZ propagated westward and began to weaken; and 1200 GMT 24 January–1200 GMT 27 January, when it disappeared.
The major findings include 1) the buildup of high pressure in the eastern Pacific coincident with the westward movement of the SPCZ, followed by a rapid buildup of high pressure over the central Pacific and demise of the SPCZ; 2) a trend from middle and upper tropospheric wavelike patterns in wind, temperature and height to more zonally-oriented patterns when the SPCZ disappears; and 3) strong cross-equatorial flow from the SPCZ into the Northern Hemisphere during the first period and strong poleward flow from the SPCZ into middle latitudes during the first two periods.
Abstract
A modified set of Level III-b grid point analyses, originally produced by ECMWF, is used to diagnose the circulation features and energy conversions in the Southern Hemisphere during the FGGE SOP-1 period of 10–27 January 1979. One of the dominant features during the period was the South Pacific Convergence Zone (SPCZ), a large-scale, quasi-stationary, convectively-active cloud band over the South Pacific Ocean. The study focuses on the significance of the SPCZ on Southern Hemisphere energy conversions by partitioning the conversions into zonal and eddy (transient and standing) components. The mean state is examined for a 15-day period, 10–24 January, when the SPCZ was most active. After 24 January it dissipated. In addition, daily variations are examined for the entire period and a zonal wavenumber analysis fox. wavenumbers 1–15 is performed.
The major findings are that 1) the baroclinic conversion of eddy potential to eddy kinetic energy (CE) is the dominant conversion term in the tropics (0–30°S), and it is particularly important in the vicinity of the SPCZ; 2) all conversion terms in middle latitudes (30–60°S) are comparable and equally important; 3) standing (transient) eddies make the most significant contribution to CE (all eddy conversion terms) in the tropics and SPCZ area (midlatitudes); 4) wavenumber 4 dominates the CE conversion in the tropics, whereas wavenumbers 5–8 dominate all the eddy conversions in middle latitudes; 5) one of the four waves in the n=4CE conversion in the tropics coincides with the SPCZ, while the remaining three correspond to the continental areas of Africa, Australia and South America; and 6) during the last three days, when the SPCZ is decaying, the importance of the n=4 contribution to CE is negligible.
Abstract
A modified set of Level III-b grid point analyses, originally produced by ECMWF, is used to diagnose the circulation features and energy conversions in the Southern Hemisphere during the FGGE SOP-1 period of 10–27 January 1979. One of the dominant features during the period was the South Pacific Convergence Zone (SPCZ), a large-scale, quasi-stationary, convectively-active cloud band over the South Pacific Ocean. The study focuses on the significance of the SPCZ on Southern Hemisphere energy conversions by partitioning the conversions into zonal and eddy (transient and standing) components. The mean state is examined for a 15-day period, 10–24 January, when the SPCZ was most active. After 24 January it dissipated. In addition, daily variations are examined for the entire period and a zonal wavenumber analysis fox. wavenumbers 1–15 is performed.
The major findings are that 1) the baroclinic conversion of eddy potential to eddy kinetic energy (CE) is the dominant conversion term in the tropics (0–30°S), and it is particularly important in the vicinity of the SPCZ; 2) all conversion terms in middle latitudes (30–60°S) are comparable and equally important; 3) standing (transient) eddies make the most significant contribution to CE (all eddy conversion terms) in the tropics and SPCZ area (midlatitudes); 4) wavenumber 4 dominates the CE conversion in the tropics, whereas wavenumbers 5–8 dominate all the eddy conversions in middle latitudes; 5) one of the four waves in the n=4CE conversion in the tropics coincides with the SPCZ, while the remaining three correspond to the continental areas of Africa, Australia and South America; and 6) during the last three days, when the SPCZ is decaying, the importance of the n=4 contribution to CE is negligible.
Abstract
A multigrid finite-difference solver is developed for the Helmholtz equation on the sphere. The finite-difference grid resolution is constant in the latitudinal direction and variable in the longitudinal direction so as to keep the physical gridpoint spacing approximately uniform over the sphere. The cpu time per grid point required to reduce the residual by a given amount is independent of grid resolution. The discretization error is slightly worse than second order as a result of the variable grid spacing. The method should be applicable to general elliptic equations on the sphere and should be useful for problems where uniform grid spacing is disadvantageous.
Abstract
A multigrid finite-difference solver is developed for the Helmholtz equation on the sphere. The finite-difference grid resolution is constant in the latitudinal direction and variable in the longitudinal direction so as to keep the physical gridpoint spacing approximately uniform over the sphere. The cpu time per grid point required to reduce the residual by a given amount is independent of grid resolution. The discretization error is slightly worse than second order as a result of the variable grid spacing. The method should be applicable to general elliptic equations on the sphere and should be useful for problems where uniform grid spacing is disadvantageous.
Abstract
A new nonlinear artificial intelligence ensemble prediction (NAIEP) model has been developed for predicting typhoon intensity based on multiple neural networks with the same expected output and using an evolutionary genetic algorithm (GA). The model is validated with short-range forecasts of typhoon intensity in the South China Sea (SCS); results show that the NAIEP model is clearly better than the climatology and persistence (CLIPER) model for 24-h forecasts of typhoon intensity. Using identical predictors and sample cases, predictions of the genetic neural network (GNN) ensemble prediction (GNNEP) model are compared with the single-GNN prediction model, and it has been proven theoretically that the former is more accurate. Computation and analysis of the generalization capacity of GNNEP also demonstrate that the prediction of the ensemble model integrates predictions of its optimized ensemble members, so the generalization capacity of the ensemble prediction model is also enhanced. This model better addresses the “overfitting” problem that generally exists in the traditional neural network approach to practical weather prediction.
Abstract
A new nonlinear artificial intelligence ensemble prediction (NAIEP) model has been developed for predicting typhoon intensity based on multiple neural networks with the same expected output and using an evolutionary genetic algorithm (GA). The model is validated with short-range forecasts of typhoon intensity in the South China Sea (SCS); results show that the NAIEP model is clearly better than the climatology and persistence (CLIPER) model for 24-h forecasts of typhoon intensity. Using identical predictors and sample cases, predictions of the genetic neural network (GNN) ensemble prediction (GNNEP) model are compared with the single-GNN prediction model, and it has been proven theoretically that the former is more accurate. Computation and analysis of the generalization capacity of GNNEP also demonstrate that the prediction of the ensemble model integrates predictions of its optimized ensemble members, so the generalization capacity of the ensemble prediction model is also enhanced. This model better addresses the “overfitting” problem that generally exists in the traditional neural network approach to practical weather prediction.
Abstract
The Weather Research and Forecasting (WRF) model–based variational data assimilation system (WRF-Var) has been extended from three- to four-dimensional variational data assimilation (WRF 4D-Var) to meet the increasing demand for improving initial model states in multiscale numerical simulations and forecasts. The initial goals of this development include operational applications and support to the research community. The formulation of WRF 4D-Var is described in this paper. WRF 4D-Var uses the WRF model as a constraint to impose a dynamic balance on the assimilation. It is shown to implicitly evolve the background error covariance and to produce the flow-dependent nature of the analysis increments. Preliminary results from real-data 4D-Var experiments in a quasi-operational setting are presented and the potential of WRF 4D-Var in research and operational applications are demonstrated. A wider distribution of the system to the research community will further develop its capabilities and to encourage testing under different weather conditions and model configurations.
Abstract
The Weather Research and Forecasting (WRF) model–based variational data assimilation system (WRF-Var) has been extended from three- to four-dimensional variational data assimilation (WRF 4D-Var) to meet the increasing demand for improving initial model states in multiscale numerical simulations and forecasts. The initial goals of this development include operational applications and support to the research community. The formulation of WRF 4D-Var is described in this paper. WRF 4D-Var uses the WRF model as a constraint to impose a dynamic balance on the assimilation. It is shown to implicitly evolve the background error covariance and to produce the flow-dependent nature of the analysis increments. Preliminary results from real-data 4D-Var experiments in a quasi-operational setting are presented and the potential of WRF 4D-Var in research and operational applications are demonstrated. A wider distribution of the system to the research community will further develop its capabilities and to encourage testing under different weather conditions and model configurations.
