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.

Sensitivity studies on the impacts of Tibetan Plateau snowpack pollution on the Asian hydrological cycle and monsoon climate

Abstract: . The Tibetan Plateau (TP) has long been identified to be critical in regulating the Asian monsoon climate and hydrological cycle. In this modeling study a series of numerical experiments with a global climate model are designed to simulate radiative effect of black carbon (BC) and dust in snow, and to assess the relative impacts of anthropogenic CO2 and carbonaceous particles in the atmosphere and snow on the snowpack over the TP and subsequent impacts on the Asian monsoon climate and hydrological cycle. Simulations results show a large BC content in snow over the TP, especially the southern slope. Because of the high aerosol content in snow and large incident solar radiation in the low latitude and high elevation, the TP exhibits the largest surface radiative flux changes induced by aerosols (e.g. BC, Dust) in snow compared to any other snow-covered regions in the world. Simulation results show that the aerosol-induced snow albedo perturbations generate surface radiative flux changes of 5–25 W m−2 during spring, with a maximum in April or May. BC-in-snow increases the surface air temperature by around 1.0 °C averaged over the TP and reduces spring snowpack over the TP more than pre-industrial to present CO2 increase and carbonaceous particles in the atmosphere. As a result, runoff increases during late winter and early spring but decreases during late spring and early summer (i.e. a trend toward earlier melt dates). The snowmelt efficacy, defined as the snowpack reduction per unit degree of warming induced by the forcing agent, is 1–4 times larger for BC-in-snow than CO2 increase during April–July, indicating that BC-in-snow more efficiently accelerates snowmelt because the increased net solar radiation induced by reduced albedo melts the snow more efficiently than snow melt due to warming in the air. The TP also influences the South (SAM) and East (EAM) Asian monsoon through its dynamical and thermal forcing. Simulation results show that during boreal spring aerosols are transported by southwesterly, causing some particles to reach higher altitude and deposit to the snowpack over the TP. While BC and Organic Matter (OM) in the atmosphere directly absorb sunlight and warm the air, the darkened snow surface polluted by BC absorbs more solar radiation and increases the skin temperature, which warms the air above through sensible heat flux. Both effects enhance the upward motion of air and spur deep convection along the TP during the pre-monsoon season, resulting in earlier onset of the SAM and increase of moisture, cloudiness and convective precipitation over northern India. BC-in-snow has a more significant impact on the EAM in July than CO2 increase and carbonaceous particles in the atmosphere. Contributed by the significant increase of both sensible heat flux associated with the warm skin temperature and latent heat flux associated with increased soil moisture with long memory, the role of the TP as a heat pump is elevated from spring through summer as the land-sea thermal contrast increases to strengthen the EAM. As a result, both southern China and northern China become wetter, but central China (i.e. Yangtze River Basin) becomes drier – a near-zonal anomaly pattern that is consistent with the dominant mode of precipitation variability in East Asia. The snow impurity effects reported in this study likely represent some upper limits as snowpack is remarkably overestimated over the TP due to excessive precipitation. Improving the simulation of precipitation and snowpack will be important for improved estimates of the effects of snowpack pollution in future work.

Global Monthly Precipitation Estimates from Satellite-Observed Outgoing Longwave Radiation

Abstract: The relationship between the flux of outgoing longwave radiation (OLR) estimated from satellite observations and precipitation is investigated using monthly OLR data from the NOAA polar-orbiting satellites and the merged analysis of precipitation of Xie and Arkin for the 8-yr period from July 1987 to June 1995. The mean annual cycle of OLR in the Tropics is dominated by changes in cloudiness and exhibits a strong negative correlation with precipitation, while in the extratropics the strongest influence on the annual cycle of OLR is surface temperature and a positive correlation with precipitation is found. However, the anomaly of OLR exhibits a negative correlation with precipitation over most of the globe. The regression coefficient relating the anomaly of precipitation to that of OLR is spatially inhomogeneous and seasonally dependent but can be expressed with high accuracy as a globally uniform linear function of the local mean precipitation. Based on these results, a new technique is develope...

Empirical Data on Contemporary Global Climate Changes (Temperature and Precipitation)

Abstract: New data are presented on the changes of mean global surface air temperature and annual precipitation over extratropical continents of the Northern Hemisphere. Global warming occurred during the last century with a mean trend of 0.5°C/100 years. It is shown that for the same period the annual precipitation over the land in the 35°–70°N zone increased by 6%. The observed variations of precipitation coincide with the results of general circulation modeling of doubled CO2 equilibrium climate change by sign but contradict by scale.

Acid precipitation: natural versus anthropogenic components.

Abstract: The concentrations of H+, SO42-, and NO3- in the precipitation of eastern North America are greater now than they were historically as a result of fossil-fuel combustion. Because of a lack of data prior to 1950, the absolute increases in the concentrations of these three ions are unknown. This problem can be addressed by comparing the composition of precipitation from areas sensitive to acidic deposition with that of precipitation from remote areas. An analysis of precipitation data indicates that many areas of eastern North America receive precipitation with substantially greater H+, SO42-, and NO3- concentrations than remote areas. For example, SO42-, the most ecologically significant indicator of change, is enriched 2 to 16 times in eastern North American precipitation relative to its concentration in remote areas.

Variability of midtropospheric moisture and its effect on cloud-top height distribution during TOGA COARE

Abstract: The tropical western Pacific warm pool is often generalized to be a region of heavy precipitation. This concept is useful in constructing simplified models of the tropical circulation. However, the warm pool region is often punctuated by periods of little rain. Such drought periods may last up to 10 days over an area of at least 6 3 105 km2. Other common features of the drought periods include an extremely dry midtroposphere, few deep clouds typically associated with mesoscale convective systems, and a substantial amount of clouds that are too tall to be categorized as trade cumuli but too short to fall into the category of deep convective clouds. Midtropospheric moisture varies substantially (60% in relative humidity ,4gk g 21 in water vapor mixing ratio) between rainy and drought periods. The frequency distributions of humidity exhibit bimodal structures at certain levels above the freezing level. In either rainy or drought periods, or in a long period including both, the time-mean humidity above the boundary layer deviates substantially from the most frequent profile of humidity, defined as the relative humidity corresponding to the maximum frequency distribution at each level. Mean soundings, therefore, do not accurately represent the overall vertical structure of moisture in the warm pool. Calculations of a simple parcel model demonstrate that the warm pool atmosphere above the boundary layer can be dry enough to discourage the growth of deep convective clouds by depleting parcel buoyancy through entrainment. These results were drawn from an analysis of soundings collected during the Intensive Observing Period (1 November 1992‐28 February 1993) of the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment.