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- Author or Editor: N. Dris x
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Abstract
Two recent reference atmosphere models for ozone and temperature, which are deduced from satellite data, are employed to detect the existence and the behavior of a terannual wave both in ozone and temperature.
Through the photochemical and the radiative processes, physical considerations are given in an attempt to explain the cause of the formation of the terannual wave.
Abstract
Two recent reference atmosphere models for ozone and temperature, which are deduced from satellite data, are employed to detect the existence and the behavior of a terannual wave both in ozone and temperature.
Through the photochemical and the radiative processes, physical considerations are given in an attempt to explain the cause of the formation of the terannual wave.
Abstract
Numerous numerical models are developed to predict long-range transport of hazardous air pollution in connection with accidental releases. When evaluating and improving such a model, it is important to detect uncertainties connected to the meteorological input data. A Lagrangian dispersion model, the Severe Nuclear Accident Program, is used here to investigate the effect of errors in the meteorological input data due to analysis error. An ensemble forecast, produced at the European Centre for Medium-Range Weather Forecasts, is then used as model input. The ensemble forecast members are generated by perturbing the initial meteorological fields of the weather forecast. The perturbations are calculated from singular vectors meant to represent possible forecast developments generated by instabilities in the atmospheric flow during the early part of the forecast. The instabilities are generated by errors in the analyzed fields. Puff predictions from the dispersion model, using ensemble forecast input, are compared, and a large spread in the predicted puff evolutions is found. This shows that the quality of the meteorological input data is important for the success of the dispersion model. In order to evaluate the dispersion model, the calculations are compared with measurements from the European Tracer Experiment. The model manages to predict the measured puff evolution concerning shape and time of arrival to a fairly high extent, up to 60 h after the start of the release. The modeled puff is still too narrow in the advection direction.
Abstract
Numerous numerical models are developed to predict long-range transport of hazardous air pollution in connection with accidental releases. When evaluating and improving such a model, it is important to detect uncertainties connected to the meteorological input data. A Lagrangian dispersion model, the Severe Nuclear Accident Program, is used here to investigate the effect of errors in the meteorological input data due to analysis error. An ensemble forecast, produced at the European Centre for Medium-Range Weather Forecasts, is then used as model input. The ensemble forecast members are generated by perturbing the initial meteorological fields of the weather forecast. The perturbations are calculated from singular vectors meant to represent possible forecast developments generated by instabilities in the atmospheric flow during the early part of the forecast. The instabilities are generated by errors in the analyzed fields. Puff predictions from the dispersion model, using ensemble forecast input, are compared, and a large spread in the predicted puff evolutions is found. This shows that the quality of the meteorological input data is important for the success of the dispersion model. In order to evaluate the dispersion model, the calculations are compared with measurements from the European Tracer Experiment. The model manages to predict the measured puff evolution concerning shape and time of arrival to a fairly high extent, up to 60 h after the start of the release. The modeled puff is still too narrow in the advection direction.
Abstract
The main objective of the present paper is the use of a constant volume balloon (CVB) as a tool to (i) study trapped lee waves and (ii) assess the forecasting capability of a nonhydrostatic numerical model. Then, CVB data obtained during the Pyrénées Experiment (PYREX) are compared with nonhydrostatic two-dimensional trapped lee waves simulated by the Meso-NH model. This model is a community research model based on the Lipps–Hemler form of the anelastic system, which has been recently developed by the CNRM of Météo-France and the Laboratoire d’Aérologie of Université Paul Sabatier in France.
To analyze how the CVB responds to lee waves, a simple CVB model is first applied to academic atmospheric stationary wave flows, analogous to those encountered during PYREX. This model takes into account the vertical velocity of the surrounding air, geometrical parameters of the balloon, and the atmospheric heating processes. Results show that the CVB reacts well to the atmospheric wave period, with a phase delay of only a few minutes.
Three CVB trajectories obtained during the third Intensive Observation Period of PYREX are then computed within Meso-NH 2D simulations from the balloon’s starting point, using the CVB model. The simulated quantities are compared to the experimental CVB data, focusing especially on the lee-wave vertical movements. The simulated lee-wave vertical velocities and amplitude are found to be in good agreement with the observations, as shown by the statistical analysis. The computed CVB heights deviate by less than 13% from the altitude of the measured trajectories. This comparison of the model output to the CVB experimental data demonstrates the good performance of the Meso-NH model in the prediction of the vertical excursions of the lee waves.
Abstract
The main objective of the present paper is the use of a constant volume balloon (CVB) as a tool to (i) study trapped lee waves and (ii) assess the forecasting capability of a nonhydrostatic numerical model. Then, CVB data obtained during the Pyrénées Experiment (PYREX) are compared with nonhydrostatic two-dimensional trapped lee waves simulated by the Meso-NH model. This model is a community research model based on the Lipps–Hemler form of the anelastic system, which has been recently developed by the CNRM of Météo-France and the Laboratoire d’Aérologie of Université Paul Sabatier in France.
To analyze how the CVB responds to lee waves, a simple CVB model is first applied to academic atmospheric stationary wave flows, analogous to those encountered during PYREX. This model takes into account the vertical velocity of the surrounding air, geometrical parameters of the balloon, and the atmospheric heating processes. Results show that the CVB reacts well to the atmospheric wave period, with a phase delay of only a few minutes.
Three CVB trajectories obtained during the third Intensive Observation Period of PYREX are then computed within Meso-NH 2D simulations from the balloon’s starting point, using the CVB model. The simulated quantities are compared to the experimental CVB data, focusing especially on the lee-wave vertical movements. The simulated lee-wave vertical velocities and amplitude are found to be in good agreement with the observations, as shown by the statistical analysis. The computed CVB heights deviate by less than 13% from the altitude of the measured trajectories. This comparison of the model output to the CVB experimental data demonstrates the good performance of the Meso-NH model in the prediction of the vertical excursions of the lee waves.
