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

The paper discusses a lower to middle tropospheric temperature record obtained from a satellite micro-wave sounder (MSU) using channel 2R. The temperature record, giving monthly mean temperatures for the 18 years from 1979 to 1996, inclusive, and for the two hemispheres and the Globe, are analysed with the purpose of finding long term trends. A comparison is made with temperature records using standard data.

"Warming world" analogue model diagnosis of total cloud amount trends is reviewed. Using cloud amount records for the continental U. S. A. (published), Canada, including parts of the Arctic (in preparation), Europe (published) and the Indian sub-continent (new results), cloudiness changes have been analyzed in the context of the analogue model which compares records of two contrasting twenty year periods. Cloud amount is found to increase over practically the entire U. S. A., Canada, most of the Indian sub-continent, and parts of Europe in all seasons. These results have been derived for a wide range of climates and considerably strengthen the more tentative findings of Henderson-Sellers (l986a, b) and MeGuffie and Henderson-Sellers (1987) that total cloud amount increases in a warming world. On the other hand, the record of total cloud amount since the 1900s has suffered from changes in observing and reporting practice from differing emphasis on observer training and from time sampling biases. These aspects of the record are considered here in detail. Moreover it must be recognized that the historical record reviewed here is land-based only, contained within the northern hemisphere and excludes many areas especially the tropics and equatorial regions. The results achieved so far could indicate that the current real-world transient experiment in which CO2 and temperatures are increasing includes a negative feedback on increasing temperatures due to increasing cloud amount. However the very restricted area considered also means that the apparent trend may be much less than global. Specifically results are not inconsistent with numerical model predictions of storm tracks shifted poleward in doubled CO2 experiments. At the least, the predictions of cloud changes made by numerical models could be re-examined in the light of the results described here.

The present work consists of two parts. In the first, an experiment is described to study the topographic forcing on the baroclinic flow. By comparison of the experiments with and without topography, the role of topography in the formation of the flow regimes is discussed. The experiments show that the travelling waves strongly vacillate with time due to the topographic forcing. Otherwise in the experiments with the same imposed external conditions but with no topography, the baroclinic waves would travel regularly with almost no vacillation. It was found that a prominent feature in the flow with topographic forcing is large-scale wave vacillation with a period of 127 annulus rotations, which is equivalent to approximately 26 days in the Earth atmosphere. The experiments show that the role of topography is to modulate the unstable baroclinic waves both in space and time. In the second part of this paper, a series of comparative experiments is introduced to study the influences of heat sources and topography on the large-scale baroclinic background flows defined as the flow patterns determined by Ω the angular velocity of the annulus rotation and ΔT, the radial temperature difference between the inner and outer walls of the annulus. The flow patterns depend on the number and disposition of the disturbance sources. As the result of nonlinear forcing of imposed heat sources the initial-axisymmetric-annular flow turns into a 4 wave flow if the number of the disturbance sources is equal to or less than two no matter which kind of disturbances, the heat source or topography, is. This means that although the mechanisms of thermo-'convective forcing of the heat sources and solid-mechanical forcing of bottom topography are essentially different, both of them can change the vorticity distribution in the flow and form new flow patterns. When the initial flow is axisymmetric-wavy owing to the forcing of heat sources, the flow becomes unstable. Either the local waves deform or vacillation occurs.

The interannual variations of the El Niño/Southern Oscillation phenomenon (ENSO) and the North Atlantic Oscillation (NAO) are statistically analysed in the time and frequency domain using time series of the following monthly indices: Two Pacific sea surface temperature indices reflecting the El Niño events (1870-1983) and two sea level pressure indices monitoring the Southern Oscillation (1882-1987) and the NAO (1881-1984). The variance spectrum analysis of these time series (with a high spectral resolution) in an "integrated" (conventional) and a "dynamic" (moving with time) way is based on both the autocovariance and the maximum entropy method. The "integrated" variance spectra reveal significant peaks at periods of 2.3, 2.9, 3.5 and 6 years for the ENSO indices and of 1.7, 2.2 and 7.5 years for the NAO index. Some of these spectral features appear to be quasi-stationary in the "dynamic" view. The statistical results are helpful in identifying and interpreting physical mechanisms associated with these large-scale oceanic/ atmospheric circulation patterns, particularly with respect to the important role of oceanic wave dynamics in the ENSO cycle.

The mineral aerosol fraction in the southwest zone of Mexico City is about 25% (40µ g/m3 approximately) of the total of suspend particles. When analyzing the mineral fraction by X-Ray Difraction, the main compounds detected are quartz, tridimite, cristonalite, feldspars, calcite and irin oxides, furthermore the elemental chemical analysis by X-Ray Spectrometry confirms the correspondence with crystalline phases revealed by Diffraction.

A three component model, somewhat more general than a recent model of Lorenz, is studied in order to illustrate the possibilities for quasi-resonant interaction of long baroclinic waves and thermal-monsoonal forcing. The model is shown to be capable of exhibiting a "folded resonance" equilibrium portrait suggestive of that which seems to be required to account for the observed bimodality of the atmospheric long-wave amplitude. One of the modes is associated with a stable, equilibrated, thermally forced wave, while the other is associated with a stable limit cycle about an unstable equilibrium. This limit cycle is activated in winter, leading to vacillatory fluctuations characterized by a long residence in a state of high amplitude and fixed phase that may correspond to one of the two modes observed.

By applying a method of linear regression, it was possible to relate the surface wind shift with respect to the wind direction at 850 mb as function of time of day, actual synoptic situation, wind speed at 850 mb, atmospheric stability, existence of thermal inversions up to 850 mb, and cloudiness. The correlation coefficients obtained in the computations were high, but the sample sizes were small.

Graphical representations for the vertical plume spread parameter, σz require digitisation for implementation in numerical calculations of plume spread. Current algebraic representation for these curves (developed from the original Pasquill-Gifford-Turner curves) centres on determining a "best-fit" regression together with other empirical evidence. Here an observationally validated conceptual model based on turbulent mixing theory is proposed for the quantification of the PGT curves for neutral and stable conditions.

Rainfall probability data from five meteorological stations in the peninsula of Baja California were analized. A simple method for characterizing geographical regions with a high interannual variability in the rainfall is proposed in this paper. The results agree with previous descriptions but also add valuable information in terms of gradients of climatic unpredictability.

Studies of the overall themodynamic and "chaotic" behaviour (Ruelle, 1985) of thr Earth-atmosphere climate system require long time-series of the total solar radiation absorbed by the system and of the total infrared radiation emitted by system. The series should extend several years in order to examine fluctuations of net energy input on time scales of several days to several months.