Showing papers in "Atmosfera in 1988"

Local wind and air pollution interaction in the Mexico basin

Abstract: Components of the thermotopographic wind regime in the Mexico City basin are examined in their interaction with the heat island induced centripetal circulation. The resulting wind regime is such that convergent surface flow over the city is predominant mainly during the night and early morning. The low-level convergence of air flow into the city, although weakened by turbulence and up-slope valley winds is still evident on daytime mean maps of resultant winds from a network of 9 stations. The position of the maximum SO 2 isolines is almost coincident with the corresponding position of the heat island. It is concluded that, for the period examined, the local thermally generated winds in Mexico City tend to restrict the ventilation of the polluted air near the surface.

Volcanic activity parameters and volcanism-climate relationships within the recent centuries

Abstract: The ejecta ofvolcanism, including gas-to-particle conversions, form atmospheric aerosol layers which influence the radiation processes and in consequence the climate. Thereby, the major explosive eruptions are of predominant interest. They cause stratospheric warmings whereas the atmospheric boundary layer near surface is cooled. In order to study these effects, focussed on air temperature variations within the recent centuries (stratosphere only since 1958) a new volcanic activity index "SVI" is denned based on the Smithsonian volcano chronology. This parameter is compared with other similar parameters and used for an stratosphere-troposphere analysis of volcanic forcing. A long-term statistical analysis uses correlation and coherence techniques "integrated" and moving with time, considering the annual and 10 yr low-pass filtered data. The air temperature time series refer to the Northern Hemisphere and Arctic mean as well as to the stations Philadelphia (USA) and Hohenpeissenberg (FRG). In general, the long-term volcanism-climate relationships may be more pronounced than singular events. Finally, a moving signal analysis is performed where the volcanic signals in climate and the signal-to-noise ratios exceed the 95% confidence level in some cases.

Influencia de los ciclones en la precipitacion de baja california sur

Abstract: Based on 20 years of daily data the precipitation patterns of Baja California Sur, Mexico are studied as well as the precipitation during the passage of the cyclones which came within 250 km of its coast. the 30 cyclones here treated have a moderate average contribution (20%) to the annual precipitation and show a different precipitation pattern from the annual values. however the recharge to the acquifers may still benefit from the observed heavy localized rains during the passage of some cyclones or at times like in 1967 and 1977 when the cyclones contributed to about 45 and 69% of the annual precipitation.

Interactive long wave spectrum for the thermo dynamic model

Abstract: Smith's (1969) analytical absorption spectrum of the atmosphere is incorporated in a thermodynamic model. This radiative formulation is applied to the infrared region. It computes separately the absorptivity by carbon dioxide and by water vapor, with a high wave length resolution, as a function of atmospheric pressure, temperature and gas content. The precipitable water or H 2 O content is computed using Adem's (1967) formula as a function of variables evaluated in the model: the surface temperature, the mid-tropospheric temperature and the horizontal extent of cloudiness. With this approach the model is able to simulate the positive feedback effect by long wave opacity of water vapor; that is to say its greenhouse effect. The computed spectrum for present values of CO 2 and H 2 O concentrations shows good agreement with the estimates of Goody and Robinson (1951), Goody (1954) and Fleagle and Businger (1963).

Possible causes and numerical simulation of the northern hemispheric climate during the last deglaciation

Abstract: A thermodynamic climate model is used to simulate the Northern Hemisphere climates for 18, 13, 10, 7 and 4 kyr BP, and to evaluate the importance of the ice sheets, the insolation anomalies and the variation of the atmospheric CO 2 in the maintainance and evolution of the terrestrial climates from 18 kyr BP to present time. The computations show the great importance of the insolation anomalies, due to orbital variations, in the annual cycle of climate, especially for the most recent period from about 12 kyr BP to present time, when the computed monthly average Northern Hemisphere surface temperature anomalies have the pattern of negative and positive anomalies shown in the insolation anomalies, except for a lag associated with the storage of heat in the oceans. It is shown that from 18 to 12 kyr BP the surface albedo feedback effect, due to the presence of ice sheets, maintains the average Northern Hemisphere surface temperature anomalies negative through the whole year, having its maximum effect at 18 kyr BP. The effect of the orbital variation is to produce larger seasonal variations in the surface temperatures, associated with the variations of the insolation anomalies which are non-negligible despite the fact that their annual average is negligible. The effect of the decrease of the atmospheric CO 2 is to reinforce the negative anomalies of the surface temperature. The average of the computed surface ocean temperature anomalies for 18 kyr BP, is about two thirds of the value estimated by CLIMAP (1976), and is due to the combined effect of the existance of the ice sheets, the decrease of atmospheric CO 2 and the anomalies of insolation, as external forcings.

Statistical prediction of monthly mean temperature anomalies in the United States during winter months

Abstract: Anomalies of mean monthly air temperature at 50 surface stations in the contiguous United States during the winter months of January, February and March from 1951 to 1980 are statistically screened as functions of earlier, centered or future time means of different length. Potential predictions include fields of 700 mb height, air and sea surface temperature, snow cover and ENSO indices. Future height anomalies are damped in accordance with the accuracy of daily numerical prognoses out to 10 days produced operationally at the National Meteorological Center. All statistical significance is evaluated by means of Monte Carlo simulations. The principal result is that judicious use of 1-10 day numerical height predictions offers the greatest promise for immediate improvement of monthly mean temperature forecasts.