Oxygen-18 variations of rainwater during precipitation: application of the Rayleigh model to selected rainfalls in Southern France

摘要: From March 1997 to 1999, sequential rainwater samples were collected during 12 rainfalls at Avignon, Southern France, with the objective of investigating how formation conditions affect isotopic composition most frequent rain types occurring in western Mediterranean region. Three major trends identified: (i) a descending δ18O trend, produced when cold front penetration causes rise warm and humid air masses, accompanied by adiabatic cooling precipitation. The temperature variation is predominant feature frontal rainfalls; (ii) an L-shaped which can be convective rains, initial rapid decrease followed stationary value; (iii) V-shaped final phase precipitation obeys different mechanism from first phase. Frontal may produce this trend. Three heavy selected for applying numerical Rayleigh condensation model describe their trends. Some irregularities generally monotonously decreasing trend attributed inputs new often recorded chemical variations as well. indicates that about 80, 60 45% vapour initially present was condensed. lowest fraction corresponds abundant rainfall, it due nature latter implying continuous supply condensable vapour.