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On a hemispheric scale, it is now well established that stratospheric ozone depletion has been the principal driver of externally forced atmospheric circulation changes south of the Equator in the last decades of the 20th Century. The impact of ozone depletion has been felt over the entire hemisphere, as reflected in the poleward drift of the midlatitude jet, the southward expansion of the summertime Hadley cell and accompanying precipitation trends deep into the subtropics. On a regional scale, however, surface impacts directly attributable to ozone depletion have yet to be identified. In this paper we focus on South Eastern South America (SESA), a region that has exhibited one of the largest wetting trends during the 20th Century. We study the impact of ozone depletion on SESA precipitation using output from 6 different climate models, spanning a wide range of complexity. In all cases we contrast pairs of model integrations with and without ozone depletion, but with all other forcings identically specified. This allows for unambiguous attribution of the computed precipitation trends. All 6 climate models consistently reveal that stratospheric ozone depletion results in a significant wetting of SESA over the period 1960-1999. Taken as a whole, these model results strongly suggest that the impact of ozone depletion on SESA precipitation has been as large as, and quite possibly larger than, the one caused by increasing greenhouse gases over the same period. [ABSTRACT FROM AUTHOR]

The global impacts of El Niño on precipitation have been long‐recognized, but more understanding of the mechanisms behind this influence is needed. For instance, previous studies have largely overlooked the potential impacts of El Niño on terrestrial moisture recycling (TMR). We perform a 40‐year forward tracking simulation to derive a global climatology of recycled precipitation and use a composite analysis to investigate how El Niño affects TMR. We identify seven regions where the El Niño impact on TMR is most significant and find that, in these regions, changes in precipitation and TMR are directly related: they increase or decrease together. In addition, we find a marked latitudinal contrast between the Southern Hemisphere, where TMR increases during El Niño, and the Northern Hemisphere and the tropics, where it decreases. Our results indicate that the weakening and strengthening of TMR can be behind precipitation changes caused by El Niño globally. Plain Language Summary: El Niño is recognized as a climate variability phenomenon with significant impacts on precipitation worldwide. However, the mechanisms behind these impacts are not fully understood. Here we use model simulations to argue that one of those mechanisms is the effect of El Niño on terrestrial moisture recycling (TMR), that is, the fraction of precipitation fed by atmospheric moisture originating not in the ocean but on the continents. We show that El Niño significantly affects TMR globally, especially in seven regions of South America, Africa, North America, Europe, and Asia. In these regions, precipitation and TMR increase or decrease together. We find a contrast between the South and North of the planet: during El Niño, TMR increases in the Southern Hemisphere while decreasing in the Northern Hemisphere and the tropics. Overall, our results indicate that TMR weakening or strengthening are previously overlooked mechanisms behind precipitation changes caused by El Niño globally. Key Points: El Niño exerts significant effects on terrestrial moisture recycling worldwideEl Niño's impacts on terrestrial moisture recycling are most significant in seven regions worldwidePrecipitation and terrestrial moisture recycling increase or decrease together due to El Niño [ABSTRACT FROM AUTHOR]

The majority of precipitation in central Chile falls during austral winter with the passage of surface and upper-level low pressure systems and their associated surface fronts. Earlier studies have found the presence of a terrain-parallel, low-level barrier jet during cold front passage and low-level wind convergence in the region of heaviest precipitation. This study advances these findings by developing multiyear climatologies for a rainfall event in central Chile using a broad cross section of observational datasets: the Tropical Rainfall Measuring Mission (TRMM), the Atmospheric Infrared Sounder (AIRS), the National Climatic Data Center (NCDC) Global Surface Summary of the Day (GSOD), the Integrated Global Radiosonde Archive (IGRA), the Quick Scatterometer (QuikSCAT), and the NCEP-NCAR reanalysis. For this study, a precipitation event was defined as daily rainfall exceeding a certain threshold at a Santiago observing station (Pudahuel). Climatologies were developed for a five-day period surrounding the precipitation event: the three days leading up to the day of precipitation at Pudahuel, the day of the precipitation itself, and the day after. Precipitation was found to move northeastward over the southeast Pacific toward central Chile and increase in intensity upon reaching reached the coast between 33° and 40°S. At middle levels, a pronounced 500-hPa trough moved eastward and amplified during the same period, and at the surface, an area of low pressure deepened and followed the same path to the east. In the boundary layer and lower troposphere, winds at 925 and 850 hPa became exclusively north-northwesterly, suggesting the existence of a low-level jet, and surface winds backed with time and increased in speed ahead of a well-defined cold front wind shift. As these winds became more northwesterly ahead of the upper-level trough and surface low, precipitable water values increased, and a tongue of high precipitable water air intersected the coast at the same location as the region of heaviest precipitation. These climatologies, based on hundreds of cases, together provide strong confirmation that forcing associated with an eastward-progressing upper-level trough, a terrain-parallel low-level wind maximum, and an advancing surface cold front together constitute the complex, complementary mechanisms for precipitation in central Chile. [ABSTRACT FROM AUTHOR]