Precipitation

About: Precipitation is a research topic. Over the lifetime, 32861 publications have been published within this topic receiving 990496 citations. The topic is also known as: rain & rainfall.

Interannual Variability of Summertime Convective Cloudiness and Precipitation in the Central Andes Derived from ISCCP-B3 Data

Abstract: The interannual variability of austral summer [December‐January‐February‐March (DJFM)] convective activity and precipitation in the central Andes (158‐308S) is investigated between 1983 and 1999 based on in situ rain gauge measurements, International Satellite Cloud Climatology Project (ISCCP) reduced radiance satellite data (the B3 dataset), and National Centers for Environmental Prediction‐National Center for Atmospheric Research (NCEP‐NCAR) reanalysis data. Twice-daily ISCCP-B3 calibrated infrared data, corrected for limb-darkening effects and representing equivalent blackbody temperatures Tb emitted by clouds are used to derive seasonal composites of fractional cold cloud coverage F*. Comparison of in situ rain gauge measurements with F* show a good correlation when a temperature threshold Tb 5 240 K is used to derive F*. A rotated empirical orthogonal function (REOF) applied to the seasonal estimates of F* yielded three spatially separated modes of convective activity in the south, northwest, and northeast of the central Andes. Results indicate that precipitation variability in the central Andes shows less spatial coherence than previously thought, with many years showing an antiphasing of wet/dry conditions between the northern and southern part of the study area. Regression analyses confirm the crucial role of both intensity and location of upper-air circulation anomalies with easterly wind anomalies favoring wet conditions, and westerly winds producing dry conditions. Two different forcing mechanisms are identified as main causes of upper-air zonal wind anomalies in the northern and southern part of the central Andes, respectively. Easterly wind anomalies during wet summers in the northern part are in geostrophic balance with reduced meridional baroclinicity due to low-latitude (midlatitude) cooling (warming), consistent with earlier studies. Farther to the south, easterly wind anomalies during wet summers are the result of an upper-air anticyclonic anomaly centered over southeastern South America, leading to a relaxation of the upper-air westerly winds and episodic easterly transport of humid air toward the subtropical Andes. This pattern is similar to one of the leading modes of intraseasonal variability, related to extratropical Rossby wave dispersion and modulation of the position of the Bolivian high. Correlation analysis of F* with near-surface specific humidity reveals that humidity variations in the lowlands to the east are not relevant on interannual time scales for the more humid northern part of the Altiplano. In the southern Altiplano, however, there is a significant correlation between convective activity and precipitation at high elevation and the low-level humidity content to the southeast of the Andes.

Attributing intensification of precipitation extremes to human influence

Abstract: [1] This study provides estimates of the human contribution to the observed widespread intensification of precipitation extremes. We consider the annual maxima of daily (RX1day) and 5 day consecutive (RX5day) precipitation amounts over the Northern Hemisphere land area for 1951–2005 and compare observed changes with expected responses to external forcings as simulated by multiple coupled climate models participating in Coupled Model Intercomparison Project Phase 5. The effect of anthropogenic forcings can be detected in extreme precipitation observations, both individually and when simultaneously estimating anthropogenic and naturally forced changes. The effect of natural forcings is not detectable. We estimate that human influence has intensified annual maximum 1 day precipitation in sampled Northern Hemisphere locations by 3.3% [1.1% to 5.8%, >90% confidence interval] on average. This corresponds to an average intensification in RX1day of 5.2% [1.3%, 9.3%] per degree increase in observed global mean surface temperature consistent with the Clausius-Clapeyron relationship.

Tropical drought regions in global warming and El Nino teleconnections

Abstract: [1] Climate model global warming simulations predict large regional changes in tropical rainfall, including regions of drought. Qualitatively similar changes occur during El Nino interannual variability. Using an intermediate climate model, we have identified a mechanism that creates regional reductions in precipitation at the margins of convection zones during warming. In this “upped-ante mechanism”, a warm troposphere increases the value of surface boundary layer moisture required for convection to occur. In regions of plentiful moisture supply, moisture simply rises to maintain precipitation, but this increases the moisture gradient relative to neighboring subsidence regions. Reductions in rainfall then result for those margins of convection zones that have strong inflow of air from the subsidence regions and less frequently meet the increased “ante” for convection. In simulations analyzed here, this new mechanism is the leading cause of tropical drought in the global warming case and is dominant in certain El Nino drought regions.

Forcing of wet phases in southeast Africa over the past 17,000 years

Abstract: A continuous record of hydrologic variability for the past 17,000 years at the mouth of the Zambezi River shows that hydrologic conditions in southeast Africa were controlled by variations in local insolation and migrations of the Intertropical Convergence Zone, rather than by Indian Ocean temperature. Records of hydroclimatological variability in southern Africa since the last glacial maximum have produced a conflicting picture of the relative influences of events in the remote Northern Hemisphere and the more local Indian Ocean. This paper presents a continuous record of hydrological variability for the past 17,000 years from marine sediment core drilled off the mouth of the Zambezi River. The record shows that hydrological conditions in the region were influenced by variations in local insolation and migrations of the intertropical convergence zone, which were probably driven by events in the Northern Hemisphere rather than the Indian Ocean. Intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast Africa since the Last Glacial Maximum, about 20,000 years ago. In particular, the relative importance of atmospheric and oceanic processes is not firmly established1,2,3,4,5. Southward shifts of the intertropical convergence zone (ITCZ) driven by high-latitude climate changes have been suggested as a primary forcing2,3, whereas other studies infer a predominant influence of Indian Ocean sea surface temperatures on regional rainfall changes4,5. To address this question, a continuous record representing an integrated signal of regional climate variability is required, but has until now been missing. Here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro-climatology in southeast Africa during rapid climate changes over the past 17,000 years. Our results are based on a reconstruction of precipitation and river discharge changes, as recorded in a marine sediment core off the mouth of the Zambezi River, near the southern boundary of the modern seasonal ITCZ migration. Indian Ocean sea surface temperatures did not exert a primary control over southeast African hydrologic variability. Instead, phases of high precipitation and terrestrial discharge occurred when the ITCZ was forced southwards during Northern Hemisphere cold events, such as Heinrich stadial 1 (around 16,000 years ago) and the Younger Dryas (around 12,000 years ago), or when local summer insolation was high in the late Holocene, that is, during the past 4,000 years.