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Meteorological research in time domain data extraction, radio altimetry, and application of ATS data as hydrological tool in remote tropical regions
Nimbus 4 Interrogation Recording and Location System meteorological experiment for tropical region upper atmosphere information
Atmospheric ozone data in tropical regions from Nimbus 3 IR interferometer spectrometer measurements, indicating easterly jet stream existence during summer monsoon period
The global distribution of temperature in the stratosphere from 100 to 10 mbar and the total ozone in the atmosphere are remotely sensed from the Nimbus-4 IRIS measurements for a period of about one year. The temperature and ozone data are presented in the form of monthly mean global maps. The standard deviations of temperature and ozone with respect to zonal averages are calculated. The mean and the variable state of the stratosphere are discussed with the help of these observations. The lower stratosphere in the tropical regions reveals a significant wave number one pattern in the circulation. The Arctic and Antarctic stratospheric winter circulation regimes display a different behavior apparently due to the ocean and orographic differences.
The backscatter ultraviolet instrument on the Atmosphere Explorer-E satellite has acquired a large body of stratospheric and total ozone data in the tropical region. The latitudinal variation of the ozone mixing ratio on constant pressure surfaces shows the transition from chemical domination to transport control between 5 and 10 mb. Spectral analysis of the longitudinal O3 structure reveals large wavenumber 1 and 2 patterns, although considerable activity in wavenumbers 5 through 7 sometimes appears. Longitudinal structure increases with decreasing pressure between 30 and 5 mb. The spatial variability near 5 mb must reflect similar structure in the odd nitrogen distribution which provides the major loss mechanism for ozone at this level.
In this paper some Viking infrared thermal mapping (IRTM) measurements of local Martian dust storms observed in the southern tropical region of the planet between solar longitudes of 225 and 262 deg are analyzed. The derived opacities of these storms show that in the most opaque regions of the cloud, the optical thickness may be approximately 6. Away from the individual clouds, the opacity is approximately 2, which is still about four times the background level of dustiness in the Martian atmosphere. Considerable structure in the derived opacity is found which will create corresponding variations in the atmospheric heating, which in turn may have an important feedback upon the local winds.
The statistical properties, and coverage, of satellite temperature sounding data are described. Tropical regions are observed every two days, extratropics from one to four times a day. Oceans are covered two to three times a day. Asynoptic coverage is comparable to the U.S. rawinsonde network twice daily coverage. Lack of ground truth for data sparse areas makes accuracy difficult to assess. The rms differences of layer mean temperatures obtained from collocating rawinsonde observations with satellite temperature profiles in space and time differ from rms differences of layer mean satellite temperature soundings. The FGGE satellite systems can infer the three dimensional motion field and improve the representation of the large scale state of the atmosphere.
A statistical classification method based on clustering on three-dimensional histograms is applied to the three channels of the Meteosat imagery. The results of this classification are studied for different cloud cover cases over tropical regions. For high-level cloud classes, it is shown that the bidimensional IR-water vapor histogram allows one to deduce the cloud top temperature even for semi-transparent clouds.
The zonal mean basic state sensitivity of the steady response to midlatitude mountain forcing is examined through the numerical solution of linearized shallow water equations on a sphere. The zonal mean basic state consists of meridionally varying zonal winds and meridional winds. Attention is given to cases in which the former are westerly everywhere, except within a tropical region in which they are easterly. A zonal wavenumber three mountain confined to the Northern Hemisphere midlatitudes provides the forcing. It is concluded that critical latitude effects on wave propagation are sensitive to mean meridional circulation structure in the critical latitude region of the model.
Quantitative techniques are available which allow the analysis of SAR images for the derivation of geological surface and process data. In conjunction with calibrated radar sensors operating at several incidence angles, wavelengths, and polarizations, the compilation of multiparameter radar signatures of lithological and geomorphic units can accordingly proceed for geological mapping in unknown areas. While radar image tone can be used in arid zones to derive surface micromorphology, heavily vegetated tropical regions require the analysis of radar image texture by means of Fourier techniques which decompose the image into bandpasses that represent different scales of texture.
Two Observing System Experiments were carried out at (ECMWF). The European Center for Medium Range Weather Forecasting impact of various observing systems were examined for two periods during the EGGE year: November 8 to 9, 1979 (OSE-1) and February 22 to March 7, 1979 (OSE-II). Attempts were made to understand the effect of the observing systems on both the analyses and the quality of the short and medium range forecasts. The results confirm that the impact of a particular observing system (e.g., SATEM) is dependent on the level of synoptic activity present in the areas where this particular observing system is the main soruce of meteorological information. SATOB data are also shown to be improtant for the analyses of tropical regions, whereas SATEM data are of paramount importance for the extratropical analyses over ocean areas. Aircraft data, where available, are an invaluable addition to the global observational data base. These results therefore demonstrate clearly the value of each of the observing systems. The fact that, in particular circumstances, there may be some redundancy between the systems is a strength rather than a weakness of the composite global observing system.
FGGE data and its analyses have made significant impact on the prediction community and its understanding of the atmosphere. The detail available from the FGGE data makes understanding of specific issues more precise and opens up new questions not previously recognized. The spectrum of issues to which FGGE data may be addressed includes time scales (stationary and transient), space scales (global versus local), regionality (tropics and oceans), specific weather phenomena (blocking and monsoons), and energetics. In addition to identifying and highlighting atmospheric processes, FGGE data can and were applied to improved atmospheric predictability. This was achieved through model initialization, improved parameterization of model forcing, and more thorough validation of model forecasts. Of particular interest is the increased understanding of the atmosphere and subsequently its predictability, which may be obtained through an assessment of the statistical characteristics of the FGGE data.
A simple way to build up a library of models which may be used to distinguish between the different types of vegetation and ground surfaces by means of their backscatter properties is presented. The curve of constant power received by the antenna (Gamma sphere) is calculated for the given Stokes Scattering Operator, and model parameters are adopted of the most similar library model Gamma sphere. Results calculated for a single scattering model resembling coniferous trees are compared with the Gamma spheres of a model resembling tropical region trees. The polarization which would minimize the effect of either the ground surface or the vegetation layer can be calculated and used to analyze the backscatter from the ground surface/vegetation layer combination, and enhance the power received from the desired part of the combination.
The vertical distributions, in temperate latitudes, of dimethylsulfide (DMS), SO2, radon, methanesulfonate (MSA), nonsea-salt sulfate (nss-sulfate), and aerosol Na(+), NH4(+), and NO(-) ions were determined in samples collected by an aircraft over the northeast Pacific Ocean during May 3-12, 1985. DMS was also determined in surface seawater. It was found that DMS concentrations, both in seawater and in the atmospheric boundary layer, were significantly lower than the values reported previously for subtropical and tropical regions, reflecting the seasonal variability in the temperate North Pacific. The vertical profiles of DMS, MSA, SO2, and nss-sulfate were found to be strongly dependent on the convective stability of the atmosphere and on air mass origin. Biogenic sulfur emissions could account for most of the sulfur budget in the boundary layer, while the long-range transport of continentally derived air masses was mainly responsible for the elevated levels of both SO2 and nss-sulfate in the free troposphere.
Although measurements of the column abundance of atmospheric water vapor on Mars have been made, measurements of its vertical distribution have not. How water is distributed in the vertical is fundamental to atmosphere-surface exchange processes, and especially to transport within the atmosphere. Several lines of evidence suggest that in the lowest several scale heights of the atmosphere, water vapor is nearly uniformly distributed. However, most of these arguments are suggestive rather than conclusive since they only demonstrate that the altitude to saturation is very high if the observed amount of water vapor is distributed uniformly. A simple argument is presented, independent of the saturation constraint, which suggests that in tropical regions, water vapor on Mars should be very nearly uniformly mixed on an annual and zonally averaged basis.
The fluxes and concentrations of atmospheric sulfur species were determined at ground level and from aircraft over the Amazon Basin during the 1987 wet season, providing a comprehensive description of the sulfur cycle over a remote tropical region. The vertical profile of dimethylsulfide (DMS) during the wet season was found to be very similar to that measured during the dry season, suggesting little seasonal variation in DMS fluxes. The concentrations of H2S were almost an order of magnitude higher than those of DMS, which makes H2S the most important biogenic source species in the atmosheric sulfur cycle over the Amazon Basin. Using the gradient-flux approach, the flux of DMS at the top of the tree canopy was estimated. The canopy was a source of DMS during the day, and a weak sink during the night. Measurements of sulfur gas emissions from soils, using the chamber method, showed very small fluxes, consistent with the hypothesis that the forest canopy is the major source of sulfur gases. The observed soil and canopy emission fluxes are similar to those measured in temperate regions. The concentrations of SO2 and sulfate aerosol in the wet season atmosphere were similar to dry season values.
The decay of the El Chichon perturbation to the optical depth of stratospheric aerosols at 1.02 micron, 0.525 micron, and 0.453 micron is calculated from the Stratospheric Aerosol and Gas Experiment II (SAGE II) data set for the period December 1984 to December 1988. It is found that the perturbed optical depths at middle and higher latitudes of both hemispheres exhibited an exponential decay superimposed by a seasonal oscillation with a maximum and a minimum occurring in local winter and local summer, respectively. Microphysical processes and variation of the tropopause height alone cannot explain this seasonal change of optical depth. The magnitudes of the exponential component at higher latitudes were, in general, larger than those at lower latitudes. For optical depths in tropical regions, the seasonal oscillations were small and were disturbed by the eruption of Nevado del Ruiz on November 13, 1985. The increase in the ratio of optical depth at 0.525 micron to that at 1.02 micron from about 2.0 at the beginning of 1985 to about 3.5 at the end of 1988 indicates the average size of aerosol particles in the stratosphere is diminishing since the eruption of El Chichon. The 1/e folding time for El Chichon decay derived from the SAGE II data set is in reasonably good agreement with those derived by other methods.
An intensive in situ sampling program near Marco Island, Florida during 19-23 October 1988 collected information on mangrove type, maximum canopy height, and percent canopy closure. These data were correlated with selected vegetation index information derived from analysis of SPOT multispectral (XS) data obtained on 21 October 1988. The Normalized Difference (ND) vegetation index information was the most highly correlated index with percent canopy closure (r = 0.91). Percent canopy closure information can be used as a surrogate for mangrove density which is of great value when predicting which parts of the mangrove ecosystem are at greatest risk after an oil spill occurs. Such information is very valuable when constructing oil spill Environmental Sensitivity Index (ESI) Maps for tropical regions of the world.