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

Recently, Atmosfera published a paper (Cacuci and Schlesinger, 1994), in wich we pointed out several inconsistencies, as well as omissions, in a paper by Marchuk and Skiba (1992).

The self-interaction of a rossby normal mode in a rectangular basin is studied by means of an analytical and a numerical model. The analytical approach is based on perturbation methods. At first order in the nonlinearties, the self-interaction produces a steady forcing and a transient forcing oscillating at twice the frequency of the mode. Both the steady and the transient forcing can never be resonant. the response to the steady forcing has an anticyclonic gyre in the northern half of the basin and a cyclonic one in the southern half. The direct response to the trasient forcing does not satisfy the boundary condition of no normal flow at the meridional walls. The fluid then adjusts by generating free Rossby waves (homogeneous solution) to balance out the forced flow normal to the walls. Among the components of the perturbative solution at first order, the steady solution is the most important one. The advective terms in the QG potential vorticity equation play an important role in the circulation of the basin if this relatively small; on the contrary, for the relatively big basins nonlinear terms are not important. For small amplitudes, the numerical solution agreess with the analytical solution, except for a delay in the period, i.e. the period of the numerical solution in the slightly larger (order 10% for the cases run here) than the period of  the analytical solution. This is presumably due to the effect of the discretization in the numerical model which leads to a difference between the anlytical and numerical frequency of a Rossby wave. The solution to first order differs apprecibly from numerical solution as the amplitude of the normal mode (initial condition) is increased, indicating that the analytical solution is valid for small  β-Rossby numbers

For a sample of 104 penetrations in 57 convective clouds with vertical depths up to 12.5 km, fluctuations of vertical and longitudimal wind components were measured. an il-14 instrumented aircraft was used for direct in-cloud measurements. in this paper is discussed the behaviour of spectral densities and other dynamic parameters during the 1986 experiment in the camaguey metereological site. it is concluded that vertical velocity energetic spectra of developing clouds hava a main maximum for scales near to 1 km. this maximum is produced by the supply of latent heat of condesation. average spectra in logarithmic coordinates have generally slopes near to -5/3, except near to an energetic maximum. a comparison is established between vertical draft velocities and turbulence intensities measured in 1986, the conditions were less favourable for convection.

A synoptic classification of observed anomaly fields of the monthly global sea surface temperatures (SSTs) is presented for the period of 1955-1993. The monthly anomaly fields are grouped into characteristic seven types. The Northern Hemisphere tropospheric responses to these SST types are described in terms of the geopotential height (Z) fields at 700, 500, and 300 mb and thickness fields for 700-500 mb and 500-300 mb. Each type of SST anomalies is associated with a distinct anomaly field of Z, whose characteristic patterns are consistent from the lower to upper troposphere. The climatic variations during the past four decades are depicted by the prevailing monthly SST patterns. The dominance of the El Nino - Southern Oscillation (ENSO) type anomaly fields during the recent years characterizes the climatic mode prevalent at present. Principal components of the SST anomaly fields during the period of July 1991 to December 1993 are presented for the description of the recent ENSO type SST patterns A possible utilization of defined El Nino Index (ENI) in the long-range projection of the atmospheric circulation is examined with cross-correlation between the preceding ENIs and following tropospheric circulation. The usefulness of ENIs as a predictor is indicated at the seasonal range.

In this work, a model for the short term prediction of the temperature of formation of radiation fogs is developed. the model is generated from a lineal relationship between the relative humidity and the air temperature, that in function of it the temperature of saturation of the air mass is stablished. the subsequent dcrease of temperature, necessary to produce the phenomenon (""interval of fog"") is determined considering a minimum quantity of the awater vapour that the air should contain in order that the products of condensation reach the concentration and necessary size to stablish the condition of fog. the calidity of the model is verified comparing their output upon applying it by cases of radiation fog observed in three stations of the half basin of the river Duero (Salamanca, Valladolid and Zamora), in several intervals of time, with the corresponding real values of fog formation temperature.

The quasi-geostrophic, baroclinic stability problem is solved using vertical structure functions corresponding to a vertical variation of the static stability parameter which is inversely proportional to the square of the pressure. Due to this assumption it is necessary to apply the upper boundary condition at a pressure level different from the outer limit of the atmosphere. While this technique has been used earlier, the emphasis in this paper is on the stability of jet profiles. Various jet-like profiles of the zonal wind are defined mathematically, and they are used to investigate how the stability depends on the maximum wind, the position of the jet maximum, the sharpness of the jet, and also the position of the upper boundary. A comparison is made with the stability of the advective model for which the stability may be obtained analytically. From the general, quasi-geostrophic model it is found that a short-wave cut-off exists, while instability exists for all wavelenghts larger than the cut-off wavelength, i.e. no long-wave cut-off exists. Smaller instabilities occurs when the maximum wind is around 300 hPa, when the top level is located at 30 hPa, and when the jet profiles are well rounded. A wind profile with "stratospheric easterlies" has about the same stability for Rossby waves of a few thousand kilometers as a profile with westerlies at all levels. However, for very long waves the profile with easterlies is more unstable.  

Our research was based on different kinds of auroral observatons at Belgrano Station (78.0°s, 38.8°w). we have studied 145 dark days, from March to September, 1971. We have obtained about 45% nights without identified auroral displays, because periods with bright moonlight and bizzards were rejected. Sudden enhancement of emissions occurred about 41.4%, 37.5% and 21% (for the lines of 557.7nm, 630.0 nm and 427.8nm, respectively) of the identified events. during July, August and September we have seen the increases of sudden enhancement of atomic oxygen emissions and the corresponding decreases of the nitrogen bands. The annual period of auroras observed at Belgrano Station, shows a peak at the time of the spring-equinoxe, and they are most frequent around the local midnight with a maximumat around the 3 hs (Universal Time).

The paper discusses the effect on the martian atmosphere of the distance between the center of gravity and the geometrical center of the planet. An approximate solution of the problem is obtained by considering the real surface as a large-scale orography with respect to a reference spherical planet. The resulting circulation has a maximum in the geopotential in the region, where the real planet is above the reference planet and a minimum in the geopotential on the opposite side. The resulting geostrophic winds have a strength of 10 to 30 ms-1. A second problem is the determination of the stationary quasi-geostrophic flow which is in equilibrium with the martian orography. The calculation is based on a specification of the martian orography in spherical harmonic functions with a triangular resolution in 16 components. This resolution is sufficient for the present purpose because the contribution from smaller features in the orography to the stationary flow pattern become negligible

Direct measurements of the rate of NO2 photolysis to NO and 0(3P) are reported as photolysis frequencies J(NO2) for Mexico City. These frequencies were measured using a flow reactor, where a known concentration of NO2 was photolysed for different experimental exposure times. UV radiation was measured with an Eppley UV radiometer. Comparisons with calculated values using a radiation transfer model, and Madronich's formula are shown.

The possibility of determination of some important optical and other atmospheric parameters on the basis of standard ground actinometry is shown. These parameters are: aerosol optical thickness of the clear atmosphere, optical thickness of overcast clouds broken cloud amounts and the total flux of the outgoing thermal radiation.