SEPTEMBER 2003 AMERICAN METEOROLOGICAL SOCIETY | W hy does it rain? If a parcel of air rises, it expands in the lower pressure, cools, and therefore condenses moisture in the parcel, producing cloud and, ultimately, rainfall—or perhaps snowfall. So a key ingredient is certainly the many and varied mechanisms for causing air to rise. These range from orographic uplifting as air flows over mounta...

large-scale climatic signals including ocean-atmosphere interactions, are the main factors influencing the earth’s climatic oscillations and are the most important indices in predicting of climate variables. in this research, precipitation in the next month was predicted by applying artificial neural network (ann), neuro-fuzzy network (nfn), and multiple linear regression (mlr) in semnan synopt...

This paper deals with the research of monthly precipitation trends in climatic stations in Libya and Slovakia. The non-parametric Mann-Kendall statistic test was applied to detect trends and to assess the significance of the trends in the time series. The evaluation was done for the time period from November to October. Trend analysis of rainfall data series for 1970–2010 did not show any clear...

Simple stochastic models fit to time series of daily precipitation amount have a marked tendency to underestimate the observed (or interannual) variance of monthly (or seasonal) total precipitation. By considering extensions of one particular class of stochastic model known as a chain-dependent process, the extent to which this ‘‘overdispersion’’ phenomenon is attributable to an inadequate mode...

drought is a climatic phenomenon that causes much detrimental influence on ecological environments. this research investigates the performance of meteorological drought indices in different time scales in thetajan basin in iran. indices undergone in this study include: percent normal precipitation index (pnpi), z-score index (zsi), standard precipitation index (spi), china z index (czi), modifi...