Numerical Meteorological Model Research Articles

NASA GTE TRACE A experiment (September–October 1992): Overview

An overview of the Transport and Atmospheric Chemistry near the Equator‐Atlantic (TRACE A) field mission is presented. TRACE A was conducted to provide a comprehensive investigation of the chemical composition, transport, and chemistry of the atmosphere over the tropical South Atlantic Ocean and the adjacent South American and African continents. Measurements for TRACE A consisted of a remote sensing component to derive tropospheric ozone and biomass burning patterns, an airborne atmospheric chemistry component to determine the composition of the air in the most pristine areas of our research domain as well as to characterize the photochemistry and transport of trace gas emissions from both fire and biogenic sources, a series of ozonesonde observations, and an enhanced radiosonde network and airborne meteorological measurements that provided information about the transport of trace gases and the physical processes that were responsible for their observed distributions. The data were interpreted through the use of both photochemical and meteorological numerical models. The picture that emerges from TRACE A is that widespread biomass burning in both South America and southern Africa is the dominant source of the precursor gases necessary for the formation of the huge amounts of ozone over the South Atlantic Ocean. In addition, however, the meteorology in this region of the world is favorable for the accumulation of these pollutants over the tropical Atlantic basin so that photochemical processes produce large quantities of ozone in situ. The generation of ozone occurs over scales of thousands of kilometers and is unusually enhanced in the upper troposphere where relatively high concentrations of nitrogen oxides (NOx) prevail. This latter finding suggests that convective processes (or other lifting mechanisms) may play an important role in the generation of tropospheric ozone or that there may be an additional significant upper tropospheric source of NOx, such as from lightning.

Characterizing Multiscale Variability of Zero Intermittency in Spatial Rainfall

In this paper the authors study how zero intermittency in spatial rainfall, as described by the fraction of area covered by rainfall, changes with spatial scale of rainfall measurement or representation. A statistical measure of intermittency that describes the size distribution of 'voids' (nonrainy areas imbedded inside rainy areas) as a function of scale is also introduced. Morphological algorithms are proposed for reconstructing rainfall intermittency at fine scales given the intermittency at coarser scales. These algorithms are envisioned to be useful in hydroclimatological studies where the rainfall spatial variability at the subgrid scale needs to be reconstructed from the results of synoptic- or mesoscale meteorological numerical models. The developed methodologies are demsonstrated and tested using data from a severe springtime midlatitude squall line and a mild midlatitude winter storm monitored by a meteorological radar in Norman, Oklahoma.

A Simple Method for Testing Brightness Temperatures from Satellite Microwave Radiometers

Abstract A method is proposed for testing microwave measurements from spaceborne sensors by computing collocated simulated brightness temperatures from the ECMWF numerical weather meteorological model using an atmospheric radiative transfer model and the Stogryn model for the surface emissivity. In this paper this method is tested on Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I) data. The comparison with observed brightness temperature underlines a rather good agreement for SSM/I but a significant discrepancy for SMMR in the vertical polarization, confirming that the SMMR was biased (up to 10 K). Correcting functions are proposed for SMMR 18- and 21-GHz channels, which are validated by comparing Wilheit and Chang's water vapor algorithm results and radiosonde measurements. Small biases in the SSM/I 19- and 22-GHz brightness temperatures comparison can be similarly eliminated. This calibration is validated in the same way by applying water vapor and surface w...

On the impact of valley/ridge thermally induced circulations on regional pollutant transport

The impact of thermally induced valley/ridge circulations on the regional-scale transport of pollutants is examined using a modeling approach. The approach consists of applying a numerical meteorological model which provides the wind and turbulence fields used as input to a Lagrangian dispersion model. A variety of generic simulations were performed. Results indicate a significant effect of the induced local flows and the thermal stratification on the regional-scale transport. Both the time of the day in which the cross valley/ridge transport occurs and the season of the year are found to be crucial in determining the magnitude and form of the alterations. Conceptual generalizations of the model results are presented.

Vectorizing a mesoscale meteorological model on the cyber 205

A mesoscale meteorological numerical model is chosen for performing the CYBER 205 vectorization technique. Three computational modules of the model (vertical diffusion, horizontal advection, and a computation including surface contrasts) are selected as working examples. A vectorization technique, denoted as “orthogonal vectorization,” is developed which is based on the model's computational structure and the CYBER 205's computer-parallelism and vector processing. Experimental results showed that for the selected examples, a speed-up by a factor of ten of the model execution on the CYBER 205 has been achieved. Provided further experiments and developments are performed, such an increase in executional speed is expected to produce profound impacts on mesoscale modeling in particular, and on atmospheric modeling in general.

Prévision des précipitations par les modèles numériques de météorologie dynamique

Dynamic numerical meteorological models simulate atmospheric conditions by solving the equations for the trend of the different variables describing the atmosphere. Water is a major variable in the atmosphere; precipitation is one of the results yielded by these models. The forecast of precipitation involves the identification of large scale phenomena which can be explicitly processed by the model (with a resolution of the order of 150 x 150 km) and smaller scale phenomena which are below the calculation range (convective type rains). Explicit processing takes into account the water vapor transfer, condensation and the resulting heat discharge. A simple chart of precipitation, assuming a Marshall-Palmer-type distribution of rainfall, allows the volume of water reaching the ground to be calculated, taking account of the evaporation of raindrops in non-saturated layers. Convective effects are parametered in a chart which distributes thermal energy and humidity as a function of altitude when the model indicates the existence of cloud convention, following two criteria: conditionally unstable atmosphere and positive water vapor addition at the base by convergence and evaporation. Rainfall forecasts have been made for France over 25 basins for 12 hour stretches during the day, at night and the following day. A verification criterion: I=100ad - (b+c/2)2/(a+ b+c/2)(d+ b+c/2) has been defined, in which a, b, c and d are the coefficient of the contingency table of rain observed and forecast exceeding a certain threshold. The value 100 of the index corresponds to a perfect forecast, and the value 0 describes a meteorological forecast of no value. Quality deteriorates the further forward the forecasting and the greater the rate of precipitation. Nevertheless, the model is always helpful. In addition, it can be seen that summer rain is not forecast as well as winter rain, in particular for moderate and low rainfall. These criteria relating to direct forecasts from the model can be used as a basis for assessing the improvements which can possibly be obtained through dynamic or statistical forecasts through local adjustments.