These notes provide a short summary of the field phase of the GARP Winter Monsoon Experiment. The field phase commenced on 1 December 1978, with the field operations coordinated from Kuala Lumpur. The participants included scientists and technical personnel from Malaysia, Indonesia, Thailand, the Philippines, Hong Kong, Japan, Saudi Arabia, Singapore, Australia, People's Republic of China (PRC), the U.S.S.R., and the U.S.A. The observing systems, type of experiments, mission objectives, components of overall data sets, and a preliminary evaluation are presented in this short survey.

The life cycle of Supertyphoon Hope (1979) from a tropical depression stage to intensification and its eventual weakening after landfall, some 6 days later, is followed in a real-data numerical prediction experiment. The predictions are carried out with a very high-resolution global spectral model, (Spectral resolution, triangular 170 waves). The initial data for this study are obtained from the delayed reanalysis of the Global Experiment (1979). Those were the analysis of the European Centre for Medium Range Weather Forecasts (ECMWF). Initialization is based on nonlinear normal mode with physics. The model has 12 vertical layers with staggered variables. A detailed physical-dynamical model is used for these studies. This typhoon prediction is a follow-up of a recent study (Krishnamurti et al. 1989). Here we show the prediction of the life cycle at a much higher resolution. The present study illustrates a remarkable prediction of the track, structure, and intensity of the supertyphoon at the higher resolution and raises the possibility for major improvement of tropical storm prediction with real data.

Because of the initial data uncertainties, it is inevitable that operational hurricane track forecasting practice would, in the future, follow an ensemble forecast approach. The ensemble technique is becoming increasingly popular for the middle-latitude weather forecasts. This paper focuses on an ensemble forecast methodology for the hurricane track forecast procedure.

In this study, an ensemble perturbation method is applied for hurricane track predictions using the Florida State University's Global Spectral Model with horizontal spectral resolution of T63 and 14 vertical levels.

The method is based on the premise that (a) model perturbation grows linearly during the first few days of model integration, and (b) in order to make a complete set of ensemble perturbations of hurricane forecasts, both hurricane initial position and its structure and environment need to be perturbed. The initial position of the hurricane is perturbed by displacing its original position 50 km equally toward the north, south, east, and west directions. The hurricane environment and structure perturbations can be generated by implementing EOF analysis to the differences between forecasts starting from regular analysis and randomly perturbed analysis. Only the temperature and wind fields are perturbed with the order proportional to the respective observational error. The method generates 15 ensemble members for each hurricane.

The result shows that this ensemble prediction method leads to an improvement in the hurricane track forecasts. The track position errors are largely reduced by the ensemble prediction for most of the hurricane cases that have been tested, and these forecasts are superior to the results from single-model control experiments. It is also noted that the spread of the ensemble track forecasts is useful to assess the reliability of the predictions.

The zonally asymmetric climatology of the tropical large-scale motion field is an interesting GARP topic. Understanding of the maintenance of various quasi-stationary features will be a challenging problem during the FGGE (the First GARP Global Experiment) and Monex (the Monsoon Experiment). In this paper we present some current thoughts that are relevant to the climatology of the tropical upper troposphere during the northern summer.

A review of some of the results from various numerical general circulation models and theoretical studies is presented for northern summer conditions. The relative success or failure of simulations of 200-mb climatology is discussed. It is pointed out that a proper simulation of the belt of anticyclones over the Asian highlands is somewhat crucial for a proper simulation of the summer climatology over the rest of the tropics.

Observations of the semipermanence of the Tibetan high pressure cell during northern summer at 200 mb suggests that it acts somewhat like a barrier. In order to illustrate this we consider a problem related to the evolution of barotropic non-divergent flows past a barrier. The flows are initially zonal, with speeds varying in the north-south direction according to northern summer observations. The barrier, whose shape is based on observations of a blocking thermal high, is impulsively introduced at initial time. The flows are kept zonal at frictionless walls at 25S and 45N. The initial north-south distribution of the zonal flows is shown to have no inflection point in its profile, thus it does not satisfy the necessary condition for barotropic instability. The presence of an impulsively introduced barrier, however, results in the evolution of transient as well as steady wave motions in long term numerical integrations. It is shown that a 30-day mean motion field contains many of the well known climatological features such as the African high, the mid-Atlantic trough, the mid-Pacific trough, the Mexican high and a weak easterly jet south of the Tibetan high. Calculations of kinetic energy exchanges between waves and zonal flow in this simple experiment is compared with corresponding calculations for tropical observations and recent general circulation experiments carried out by Abbott. The impulsively introduced barrier simulates an energy source for zonal wavenumber 1, quite similar to observations in a tropical belt. Although this experiment is fairly crude, it is found to be very illustrative in many respects. Many diverse experiments along these lines can be carried out to reveal various aspects of atmospheric circulations.

The deployment of a space-based Doppler lidar would provide information that is fundamental to advancing the understanding and prediction of weather and climate.

This paper reviews the concepts of wind measurement by Doppler lidar, highlights the results of some observing system simulation experiments with lidar winds, and discusses the important advances in earth system science anticipated with lidar winds.

Observing system simulation experiments, conducted using two different general circulation models, have shown 1) that there is a significant improvement in the forecast accuracy over the Southern Hemisphere and tropical oceans resulting from the assimilation of simulated satellite wind data, and 2) that wind data are significantly more effective than temperature or moisture data in controlling analysis error. Because accurate wind observations are currently almost entirely unavailable for the vast majority of tropical cyclones worldwide, lidar winds have the potential to substantially improve tropical cyclone forecasts. Similarly, to improve water vapor flux divergence calculations, a direct measure of the ageostrophic wind is needed since the present level of uncertainty cannot be reduced with better temperature and moisture soundings alone.

Rainfall is a fundamental process within the Earth's hydrological cycle because it represents a principal forcing term in surface water budgets, while its energetics corollary, latent heating, is the principal source of atmospheric diabatic heating well into the middle latitudes. Latent heat production itself is a consequence of phase changes between the vapor, liquid, and frozen states of water. The properties of the vertical distribution of latent heat release modulate large-scale meridional and zonal circulations within the Tropics, as well as modify the energetic efficiencies of midlatitude weather systems.

This paper highlights the retrieval of latent heating from satellite measurements generated by the Tropical Rainfall Measuring Mission (TRMM) satellite observatory, which was launched in November 1997 as a joint American–Japanese space endeavor. Since then, TRMM measurements have been providing credible four-dimensional accounts of rainfall over the global Tropics and subtropics, information that can be used to estimate the space–time structure of latent heating across the Earth's low latitudes.

A set of algorithm methodologies for estimating latent heating based on precipitation-rate profile retrievals obtained from TRMM measurements has been under continuous development since the advent of the mission s research program. These algorithms are briefly described, followed by a discussion of the latent heating products that they generate. The paper then provides an overview of how TRMM-derived latent heating information is currently being used in conjunction with global weather and climate models, concluding with remarks intended to stimulate further research on latent heating retrieval from satellites.

In 2006, NASA led a field campaign to investigate the factors that control the fate of African easterly waves (AEWs) moving westward into the tropical Atlantic Ocean. Aircraft and surface-based equipment were based on Cape Verde's islands, helping to fill some of the data void between Africa and the Caribbean. Taking advantage of the international African Monsoon Multidisciplinary Analysis (AMMA) program over the continent, the NASA-AMMA (NAMMA) program used enhanced upstream data, whereas NOAA aircraft farther west in the Atlantic studied several of the storms downstream. Seven AEWs were studied during AMMA, with at least two becoming tropical cyclones. Some of the waves that did not develop while being sampled near Cape Verde likely intensified in the central Atlantic instead. NAMMA observations were able to distinguish between the large-scale wave structure and the smaller-scale vorticity maxima that often form within the waves. A special complication of the east Atlantic environment is the Saharan air layer (SAL), which frequently accompanies the AEWs and may introduce dry air and heavy aerosol loading into the convective storm systems in the AEWs. One of the main achievements of NAMMA was the acquisition of a database of remote sensing and in situ observations of the properties of the SAL, enabling dynamic models and satellite retrieval algorithms to be evaluated against high-quality real data. Ongoing research with this database will help determine how the SAL influences cloud microphysics and perhaps also tropical cyclogenesis, as well as the more general question of recognizing the properties of small-scale vorticity maxima within tropical waves that are more likely to become tropical cyclones.