Vol. 108, No. 4 * Pages 209–287 * October - December 2004

In this paper the clear-sky infrared radiation field of the Earth-atmosphere system is characterized by the spectral decomposition of the simulated upward and downward flux density components into three distinct wave number regions. The relative contributions of the far infrared, middle infrared and windows spectral regions to the total longwave flux densities have been established. The approximate qualitative description of the meridional distributions of the zonal averages gave us a detailed insight into the role of the less explored far infrared spectral region. We demonstrate that on a global scale, the far infrared contribution to the clear-sky normalized greenhouse factor is significantly increasing toward the polar regions. Accurate computation of the transmitted and re-emitted part of the outgoing longwave radiation showed that in the far infrared the normalized upward atmospheric emittance increases poleward. This phenomenon is the direct consequence of the downward shift of the peak of the weighting functions in the strongly absorbing opaque spectral regions. The clear-sky total longwave terrestrial flux transmittance seems to be well correlated with the far infrared flux transmittance which implies the possibility of inferring total longwave flux densities solely from far infrared observations. The zonal averages of the total normalized atmospheric upward emittances are almost independent of the water vapor column amount, they have no meridional variation, and they are constantly about fifty percent of the surface upward flux density, an indication, that the gray atmosphere in the IR is in radiative equilibrium. The meridional distribution of the greenhouse temperature change and its dependence on the atmospheric water vapor content were also evaluated. Solving the Schwarzschild-Milne equations for the bounded atmosphere the infrared atmospheric transfer and greenhouse functions were derived. The theoretically predicted greenhouse effect in the clear atmosphere are in perfect agreement with simulation results and measurements.

Leaf wetness duration (LWD) is one of the most important variables responsible for development of plant diseases. Thus, its measurement represents the basis for disease forecasting models, developed and applied with the aim of timing fungicide application, for avoiding environmental damages, waste of resources, and money losses. Despite of its importance, there is no widely accepted standard for LWD measurement, and the different measurement principles, sensor designs, and installation positions are responsible for different results affecting the quality of model simulations. For this reason, four leaf wetness sensors were mounted in a vineyard in two different positions, at one quarter and three quarters of the canopy height, and in two expositions, east and west. Measured LWD was analyzed and compared with visual inspections conducted during the experiment in order to establish the performance obtainable from different sensor positionings, and to asses their impact on the simulation of grapevine downy mildew (Plasmopara viticola).

Annual precipitation totals of 13 stations in different parts of Serbia and Montenegro are analyzed for homogeneity, trend, and periodicities. The data cover time periods ranging from 50 to 70 years. Autocorrelation spectral analysis (ASA) and multitaper method (MTM) are used to investigate the periodicity of precipitation series. Spectral analysis shows peaks at frequencies corresponding to the following time periods: about 2.5–5, 8, and 14–23.3 years. Statistical significance of these peaks is discussed. These results are compared with those of other authors.