Explanations for simultaneous laminae in water vapor and aerosol profiles found during the SESAME experiment

An instrumented balloon launched from Kiruna during the SESAME experiment displayed simultaneous local decreases of water vapor and aerosol at 2 different potential temperature levels 410 K and 364 K. Despite the similar characteristics present at both levels, 2 different explanations are given for these laminae. At the highest level, the air mass showing the water vapor and aerosol decrease is found when the balloon travels in the vortex edge region. A back trajectory shows that this air mass was trapped in the vortex edge region for several days and processed by a PSC causing the water vapor and aerosol decreases. On the other hand, the lowest level air mass was found to be in the sub‐vortex region. No local conditions can explain the observed decreases of water vapor and aerosol. Back trajectories show that this air mass originates from middle latitudes. Although the back trajectories calculated in these conditions are more subject to caution, comparison of several characteristics at the measurement point and at the middle latitude sites corroborates the explanation of the decrease of water vapor and aerosol by the origin of the air mass.     

A very deep ozone minihole in the Northern Hemisphere stratosphere at mid‐latitudes during the winter of 2000

Ozone miniholes appear on total ozone maps as localized ozone minima with horizontal extents of a few hundreds of kilometres. They are characterized by a rapid and small‐scale appearance of a columnar ozone decrease with an equally rapid recovery after a few days. They are frequently observed at Northern Hemisphere mid‐latitudes in winter. Evolving too rapidly to be the result of an ozone chemical destruction, miniholes should be the result of meteorological processes. According to some authors, miniholes should be due to the northeast motions of air patches with low total ozone content. However, several studies attribute the formation of ozone miniholes to the uplift of air masses, which decreases the ozone columnar content by simply decreasing the pressure thickness of the ozone layer, without changing the mixing ratio. According to these studies, the latter mechanism explains the main reduction of ozone that occurs between the tropopause and the ozone maximum during an ozone minihole event. A region of extreme low ozone values passed over Europe from 27 to 30 November 2000. The total ozone values were measured with the Total Ozone Mapping Spectrometer (TOMS). A radio sounding, launched on 29 November 2000 from Payerne at the place and time of the deepening of the minihole, allows us to perform a detailed analysis of its formation mechanism. It is shown that the uplift of isentropic surfaces plays an important role in the columnar ozone decrease and explains the lower part of the depleted ozone profile. However, the deepening of the minihole is explained by another mechanism: namely, at this time the minihole air column intersects the polar vortex at high altitudes and then encounters ozone‐poor air masses.     

Transport de matières dissoutes et particulaires des Andes vers le Rio de La Plata par les tributaires boliviens (rios Pilcomayo et Bermejo) du Rio Paraguay

Résumé

Les données recueillies à 13 stations hydromètriques des réseaux du SENAMHI et de ENDE, de 1975 à 1983, permettent d'estimer les flux de matières particulaires et dissoutes dans les bassins andins des rios Pilcomayo et Bermejo, formateurs du Rio Paraguay. Les résultats obtenus en Bolivie sur le bassin versant du Rio Pilcomayo, montrent que l'essentiel de l'exportation est le fait des matières en suspension (90%). Le flux de sédiments mesuré à la sortie des Andes sur le Rio Pilcomayo (80 × 10⁶ t an^?1) est du même ordre de grandeur que Celui observé 2000 kilomètres à l'aval sur le Moyen Parana.