Vol. 111, No. 1 * Pages 1–77 * January - March 2007

In this work the theoretical relationship between the clear-sky outgoing infrared radiation and the surface upward radiative flux is explored by using a realistic finite semi-transparent atmospheric model. We show that the fundamental relationship between the optical depth and source function contains real boundary condition parameters. We also show that the radiative equilibrium is controlled by a special atmospheric transfer function and requires the continuity of the temperature at the ground surface. The long standing misinterpretation of the classic semi-infinite Eddington solution has been resolved. Compared to the semi-infinite model, the finite semi-transparent model predicts much smaller ground surface temperature and a larger surface air temperature. The new equation proves that the classic solution significantly overestimates the sensitivity of greenhouse forcing to optical depth perturbations. In Earth-type atmospheres sustained planetary greenhouse effect with a stable ground surface temperature can only exist at a particular planetary average flux optical depth of 1.841. Simulation results show that the Earth maintains a controlled greenhouse effect with a global average optical depth kept close to this critical value. The broadband radiative transfer in the clear Martian atmosphere follows different principle resulting in different analytical relationships among the fluxes. Applying the virial theorem to the radiative balance equation, we present a coherent picture of the planetary greenhouse effect.

In the evening of August 20, 2006 severe thunderstorms hit Budapest. The storm struck the downtown at the same time when the Constitution Day firework just started, killed five people and wounded hundreds of spectators crowded on the embankments of the river Danube. In this paper weather conditions from synoptic scale to storm scale are investigated to find the special circumstances, which led to formation of the devastating storm. Investigations show that a wave on a cold front, the mid level cold advection, the drift of jet stream above the warm sector, and an intense wet conveyor belt resulted in intense instability. Furthermore, the wind shear and the low level convergence also contributed to the formation of the fast moving squall line. Detailed Doppler-radar analysis proved that the thunderstorm, which crossed the downtown of Budapest, was a supercell. Comparison of the radar reflectivity and the lightning data of the investigated case with that of other severe storm cases shows that the Constitution Day storm was not an extreme event. The unique feature of this case was the extreme high speed of cell motions. High resolution numerical model (MM5) was applied to understand the dynamical structure and predictability of the storm. Model results show the importance of the layer on 3 km above ground level with high value of equivalent potential temperature and the active role of the cold front in the formation of the squall line. The model was able to simulate the structure and motion of the supercell proving the numerical predictability of this type of severe convective storms.

Results of a climatological study of soil moisture under corn crop at six stations in the semiarid region of Northeast Brazil are reported in this paper. Daily values of available soil moisture during the wet season are evaluated using a six-zone versatile soil moisture budget (VSMB) model. A first order Markov chain model is applied to the daily soil moisture data. Soil moisture averages and probabilities are used to identify the optimum growing periods for corn crop at the stations, and the irrigation needs during these periods are evaluated. The effect of soil hydro physical properties in the VSMB model is discussed. The use of mean daily precipitation values in the model in place of actual precipitation data is briefly discussed.