The effect of change in surface roughness on the precipitation regime in the coastal area of NE-Brazil

The NE of Brazil is one of the earth's problematic semiarid areas. However, in the coastal area along the coast from Natal to Salvador precipitation is high enough to allow for a fully developed tropical vegetation. It is shown that this enhancement of annual precipitation is due to the dynamic convergence within the planetary boundary layer and that this effect can quantitatively be evaluated by simple model considerations. To do this the mass flux perpendicular to the coastline is calculated within the lower troposphere for an undisturbed PBL (Planetary Boundary Layer) over land and over sea, by using the resistance law of the PBL and by integrating the equation of monion between the bottom and some height above the PBL. By using the equation of continuity the mean vertical motion due to the coastal convergence can be calculated. The relation of the calculated total amount of lifting near the coast on the rate of precipitation is calculated. Compared with the increase of precipitation due to orography it gives the same increase in precipitation per meter of lifting in the coastal area quantitatively and since this is strongly related to the roughness due to the vegetation along the coast it can be shown that deforestation — for instance to grow sugar-cane — in this area the annual amount of precipitation will decrease considerably. Once the coastal area will have been transformed to a desertlike structure, the coastal maximum of precipitation will diminish at all.     

Effects of deforestation and afforestation on climate

Forests cover 29% of the continents. Their importance for mankind is not only due to wood production but also by their manyfold influences on the biosphere. The properties of forest stands influence climate, water balance, air constituents and the dynamic of atmosphere. The welfare functions of forests can be observed in the global as well as in the local or microscale. Anthropogenic measures, as deforestation and air pollution, endanger the forests and by that one of the main pillars of nature on earth.     

Results from the MERKUR experiment: Mass budget and vertical motions in a large valley during mountain and valley wind

Summary Based on measurements made in March 1982 in the Inn valley during the MERKUR experiment, an attempt was made to compute the mass budget of a large alpine valley during periods of mountain and valley wind.The computations come from measurements of the alongvalley mass flux and assumptions on the fluxes in the slope layer and tributaries.Vertical motions in the valley's atmosphere have been evaluated from the mass budget computations. These motions, including the subsidence which compensates for daytime upslope winds and the subsidence which compensates for the valley wind flowing into tributaries during the day, are of great importance for the understanding of the thermal circulation.The results allow better estimation of vertical advection, which contributes to the budgets of momentum and energy.With 8 Figures     

Concentration of trace gases in the lower troposphere,simultaneously recorded at neighboring alpine stations Part III: Sulfur dioxide,nitrogen dioxide,nitric oxide

Summary The importance of representative and long-term recordings of the trace gases SO₂, NO _x , and NO is explained. Recordings taken under different background conditions and, moreover, simultaneously at neighboring mountain stations, together with other meteorological parameters, are of special interest.The recording stations for the determination of the mentioned gases (a valley station at 740 m a.s.l., a nearby mountain station at 1780 m a.s.l.), the measuring methods, calibration procedures, and zero-air supply are described.The main part deals with the representation of consistent data of trace gases obtained at the two stations (NO only in the valley floor). Special attention was given not only to longterm trends but also to the seasonal and diurnal variations, and to the dependence of the gas concentrations on meteorological parameters. Only on the basis of such a parameterization, the time variations become understandable and the causes can be explained as well as possible. Finally, correlations between the concentrations of the different gas components are shown.With 15 Figures     

Instability indices for the Cyprus area

Summary In this paper, forecasts of thunderstorms for the Cyprus area, are examined, by using various instability indices. In addition, some combinations of the indices are proposed since they proved more successful in thunderstorms forecasting. A statistical method pointed out that the Pickup index (PI) and the suggested combination of the humidity index (HI) with cyclonic curved flow at 500 hPa are more successful than the other ones examined in this study.With 1 Figure     

A simplified hydrodynamic mesoscale model suitable for use over high plateau regions

Summary A simplified hydrodynamic primitive equation model in -coordinates is described. This model includes the main physical processes that influence development and motion of mesoscale vortices over plateau regions: elevated terrain effects, effects of large-scale and synoptic-scale systems on the mesoscale systems, sensible heating from the earth's surface, moisture cycle and condensation heating released by both large-scale stable precipitation and cumulus convective precipitation, evaporation and the feedback effect of precipitation on evaporation, friction in the planetary boundary layer, horizontal diffusion by subgrid scale eddies and vertical eddy flux of meteorological elements (momentum, temperature, moisture, etc.) due to turbulence, cumulus convection and other smaller-scale physical processes. The model incorporates observed data as much as possible and equations are simplified so that it may be run using either a high-speed computer or a desktop computer.Two developing vortices that originated over the Qinghai-Xizang (Tibet) Platau and moved eastward producing heavy precipitation over the lower elevations are used to test the model. It is shown that the model is capable of simulating the major features of the vortices including the precipitation distribution and may be used for studies of mesoscale and synoptic scale weather systems over plateau regions.

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Ein vereinfachtes für hochländer geeignetes hydrodynamisches mesoscale-modell

Zusammenfassung Es wird ein vereinfachtes hydrodynamisches Grundgleichungsmodell in -Koordinaten be schrieben. Dieses Modell beinhaltet die wichtigsten physikalischen Prozesse, die die Entwicklung und Bewegung von mesoskaligen Wirbeln über Hochplateaus beeinflussen: Effekte der Hochfläche, Effekte von großräumigen und synoptischen Systemen, die fühlbare Wärme von der Erdoberfläche, den Feuchtigkeitskreislauf und die Kondensationswärme, sowohl von großräumigen als auch von Konvektionsniederschlägen, die Evaporation und die Beeinflussung der Evaporation durch den Niederschlag, die Reibung in der planetaren Grenzschicht, die horizontale Diffusion durch Turbulenzen, die kleiner als die Gitterkonstante sind und den vertikalen Fluß meteorologischer Elemente (Impuls, Temperatur, Feuchte etc.) durch Turbulenzen, Konvektion und andere kleinräumige Prozesse. In das Modell sind die Beobachtungswerte weitestgehend integriert und die Gleichungen soweit vereinfacht, daß es sowohl auf einem Hochleistungs- als auch auf einem Mikrocomputer laufen kann.Zum Testen des Modells wurden zwei sich entwickelnde Wirbel verwendet, die vom Qinghai-Xizang-Plateu (Hochland von Tibet) ausgingen, sich ostwärts bewegten und dabei zu schweren Niederschlägen in den Tiefländern führten. Es wird gezeigt, daß das Modell die wichtigsten Eigenschaften der Wirbel und die Niederschlagsverteilung simulieren und für Untersuchungen von mesoskaligen und synoptischen Wettersystemen über Hochländern herangezogen werden kann.

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With 18 figures