Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The well known geostrophic adjustment problem has been reinvestigated using first a model of a homogeneous atmosphere with a free surface. The basic equations in this model are the two equations of motion for the horizontal velocity components modified to contain only the east-west variations and the continuity equation treated in the same way. A linear frictional term is included in the equations, and the forcing of the model atmosphere is included in the continuity equation. The zonal case is described in Sections 2 and 3. The equations are integrated numerically from an initial state of rest and a horizontal upper surface. If geostrophic adjustment should be obtained, the zonal velocity components should be small, while the meridional velocity components should be in approximate balance with the geostrophic component computed from the zonal geopotential gradient. It is found by integrating the equations for 20 days that the above requirements are satisfied. The numerical integrations of the set of primitive equations are carried out in wave number space, but the results are presented as continuous variations in the west-east directions. It is shown that geostrophic adjustment is reach after a couple of days. The final state of the adjustment process is obtained using several specifications of the forcing. While the final states naturally are different, the geostrophic adjustment is found in each case. A case based on full Fourier series is also included in Section 3. The adjustment problem is also treated in the meridional case in section 4 and 5 using the same strategy as described above. Section 6 contains a solution of the adjustment problem using a two-level, primitive equation model maintaining only the variations in the zonal direction.

A study has been carried out to investigate the thermodynamic characteristics of the Convective Boundary Layer (CBL) over the Bay of Bengal region. For this purpose aerological observations collected from MONSOON-77 utilizing the erstwhile USSR research vessels (i. e. Shirshov, Priboy, Shokalsky and Okean) in the region 15-19 N, 87-91 E during 11-18 August 1977 and BOBMEX-98 onboard Sagar Kanya at 13ºN 87ºE have been considered. The results of the analysis showed that no marked differences are found in the Convective Boundary Layer characteristics over the four ships during the period under consideration. 6-hourly vertical profiles of the thermodynamical paramenters showed the evolution of the CBL structure during daytime at all the locations The top of the CBL is found between 700-580 hPa and it varied with time. The daily 6-hourly values of surface meteorological parameters viz, p, 1 and Td showed diurnal variation. Also, it is evident that the surface meteorological parameters as well as structure of the CBL over the region mentioned above is influenced by the prevailing weather conditions and associated synoptic/transient scale disturbances.

In this paper, an analytical study of an explosive cyclogenesis that occurred in northeastern Argentina on 11-12 November 1989, is carried out. European Centre for Medium Range Weather Forecasts Analysis data are used to compute the terms of the atmospheric motion governing equations in order to determine the triggering mechanisms of this event. This cyclogenesis is initiated by classical processes such as the advection of vorticity and divergence in the upper troposphere. The diabatic mechanisms rapidly associate to these processes, generating an intense cyclonic potential vorticity in low levels and depleting it in upper levels. The major development occurs when the presence of cyclonic vorticity in upper levels continues in spite of the mechanisms tending to weaken it.

From meteorological data and sea surface temperatures taken during the oceanographic cruises PLAYUC (January 6 to 17, 1990) and YUCPLA (May 25 to June 4, 1990), conducted over the Yucatan Continental Shelf, the cooling and heating areas produced by the fluxes of latent (Qe) and sensible heat (Qt) were determined. The computation was done using the bulk aerodynamic equations. During PLAYUC, the line of SST - Ta = 0 (sea surface temperature minus air temperature) divided roughly the study area into two regions (east and west). This was caused by two moderated northers. At the west side the difference SST - Ta was between 1 and 4ºC, and at the lower east side the difference was between -1 to -3ºC. The values of Qe and Qt for the cooling area at the west were from 160 to 260 W/m2 and from 10 to 60 W/m2 respectively. At the east portion the diurnal contrast of Qe was observed at three small areas. North of Cabo Catoche a fog was present over a weak upwelling area, reducing the cooling rate due to Qe from 30 to below 10 W/m3 and the heating due to Qt to values around -5 to -6 W/m2. The average values during PLAYUC for Qe and Qt over the shelf were 140.92 and 14.88 W/m2, respectively. During YUCPLA, influence of moist and warm air from the East was observed. Two lines of SST - Ta = 0 divided the study area diagonally in two portions, northwest and southeast. The difference SST - Ta for the northwest portion was from -1 to 0ºC and for the southeast from -4 to 0ºC. During this second cruise the cooling was less intense and with weaker spatial contrast. At the NW portion two intrusions of Qe were observed, one toward the coast and another going offshore. At the SE portion a north-to-south tongue was observed. Similar to what was the case during PLAYUC, the upwelling and fog area promoted a heating due to condensation (Qe < 0). At the NW portion three well delineated regions of heating and cooling were observed, showing the diurnal variations. The average values during this cruise for Qe and Qt were 66.63 and 0.36 W/m2, respectively.

Chaparral and conifer forest ecosystems in northern Baja California are subject to recurrent fire owing to the regions's mediterranean climate. The high frequency of burns has been attributed to deliberate burning. However lightning from summer thunderstorms are a frequent source of natural ignitions. The US lightning detection (LD) data system records and locates lightning discharges in this region. These data were entered into the ARC-INFO geographic information system (GIS) in which were calculated LD rates within vegetation types. LD densities are greatest in updraft zones along the eastern escarpments of the Sierras Juarez and San Pedro Martir. From 1985 to 1990, there were 17 to 46 times as many lightning discharges as burns occurring in both sierras. The fire refractory periods -the time between consecutive burns- are long (70-82 yr). An area of 1000 ha, which is the average size of burns in northern Baja California, receives a number of lightning strikes every few years. Consequently, few lightning strikes give rise to fire due to the scarcity of combustible biomass. The long refractory periods of the vegetation provide evidence of an inverse relation between the number and the size of burns. Given the high rates of lightning detection, ignitions provoked by man would have little impact on fire regimes.

This paper complies within the framework of our earlier studies which have dealt with recent changes of sea-air parameters and evaporation over tropical oceans. Here, based on three chosen sections - the areas on both sides of the Panama Canal and around the Galapagos Islands - we will draw a regional comparison between upwelling and warm ocean areas with regard to the variability of the selected sea-air parameters in the period 1947-1989 We examined the seasonal and annual trends, decade-to-decade changes of the averages, and the variability and relative frequency of the sea surface temperature's anomalies. Furthermore, we investigated the correlation between the individual parameters and connections between the named sections. We were able to confirm reasonably notable temporal and spatial differences in available meteorological elements.  

The contribution of atmospheric aerosols on the variation of outgoing radiation is estimated on the basis of an aerosol ensemble model, whose optical properties are defined through relative humidity and range of visibility. The influence of the albedo of the underlying surface is also taken into account. It is show n that the variations of outgoing radiation fluxes may reach tens of percent and therefore they must be taken into consideration during the solution of practical problems of remote sensing. In the infrared spectral region, the changes of outgoing thermal radiation may range from some small percentage up to the order of the value. Simple estimates show that more correct accounting for the effect of aerosol particles improves the accuracy of determining the atmospheric temperature by 0.1 to 0.2º and that of the underlying surface by 0.2 to 0.3º.

The equilibrium conditions between the orography of a planet and its atmosphere are investigated. A first relatively simple example is the solution of the problem in an equivalent barotropic atmosphere, while the two-level quasi-geostrophic model is taken as the second example. The problem can also be solved for multi-level, quasi-geostrophic models. The problem under invesigation is to find the motion which can exist in an atmosphere under steady state conditions in equilibrium with the orography of the planet. A trivial solution is a state of rest, but it is shown that non-trivial solutions can be constructed as well. The investigation is basically different from the classical problem of finding the influence of orography on a preexisting flow which has been solved in numerous cases. On the Earth with its strong meridional temperature gradient created by the differential heating between Pole and Equator and due to diabatic heating processes compensated partly by meridional transport of sensible heat the general circulation is in the first approximation determined by the processes of baroclinic instability deriving its energy from the meridional temperature field and in turn maintaining the zonal currents by heat and momentum transport primarily by the waves. On the global scales the circulation is modified greatly by the existence of continents and oceans and by orography. On other planets, with smaller meridional differential heating than the Earth, the orogrphy may have a major influence on the stationary flow pattern.  

Problems related with ecological effects produced by gaseous pollutants are of growing general concern preocupation and particularly the NO2 that is related to acid rain formation, and also to several reactions with the greenhouse effect gases. This paper reflects the influence of various meteoroligical and geographical systems during the period of 1985-1988.

Motivated by a recent article published in this journal by Marchuk and Skiba (1992), we present a brief review of the development of the adjoint method of sensitivity analysis, highlighting its limitations and applicability to both linear and nonlinear systems. In the process, the work of Marchuk and Skiba (1992) is set in perspective, both historically and mathematically.