Distribution of convective energy at upper level i

Authors: SangMin Lee HiRyong Byun

Publish Date: 2011/02/15

Volume: 105, Issue: 3-4, Pages: 537-551

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Abstract

This paper reports a theoretical study on the possibility of inducing artificial showery rain using the convective available potential energy which is naturally stored in the troposphere We calculated the environmental parameters frequency of climatic values extreme value of stability index etc in the upper troposphere using rawinsonde data from six main stations in Korea from 2001 to 2008 and examined the temporal spatial convective energy according to region Our results showed that convective available potential energy which can induce artificial rainfall existed in the troposphere mainly in summer and were low in other seasons Its value was found to be highest during late afternoon and in inland regions We examined the vertical structure of the atmosphere using moisture convergence and vertical velocity omega and found that precipitation occurred under strong real latent instability conditions with high convective available potential energy 3000 J/kg in summer and was characterized by moisture convergence at 1000–400 hPa moisture divergence at 400–300 hPa and continuous ascending air current at 1000–300 hPa –ω on average However precipitation still did not occur in more than half the cases with high convective available potential energy because according to the analysis convective rainfall is affected to a greater extent by the value of convective inhibition than by convective available potential energy It was also verified that in spite of zero convective inhibition if the updrafts at a lower level were not sufficient to generate high convective available potential energy at a level higher than the level of free convection convective rainfall would not occur under real latent instability Therefore we suggest it might be possible during the summer to secure the water resources in regions without precipitation by inducing ascending air current artificially under unstable atmospheric conditions to induce showery rainOver 50 of the annual precipitation in Korea occurs during the summer Ho and Kang 1988 This is because the influx of water vapor is intensified during the summer due to the influence of moist southwesterly wind and typhoons and the water vapor often changes into showery rain due to the instability of the atmosphere Thus the precipitation depends on the instability of the upper atmosphereThe instability of the upper atmosphere in Korea has been previously studied but the data was collected over short periods of time and only a few observation stations were used Furthermore most studies examined thunderstorm conditions and showed that air mass thunderstorms developed as a result of conditional instability in the lower atmospheric layer Heo et al 1994 the distribution of potential wetbulb temperature in the lower layer Kim and Lee 1994 and the reproduction of convective cells in the process of nonlinear advection Son et al 2000 However these studies focused on the characteristics of atmosphere in a very unstable state that appears during the development of the thunderstorm Hence the climatological temporal and spatial characteristics were not observedEom et al 2008 in a climatological study of the upper atmosphere in Korea showed that the stability index and the environmental parameters were influenced by the geographical position of the station and the seasonal variation of the vertical structure of the atmosphere due to solar energy They analyzed the upper atmosphere rawinsonde data of 5 stations in Korea for the period 1997–2006 Outside of Korea extensive studies have been carried out on upperatmospheric conditions using longterm accumulated data In those studies researchers mainly estimated the threshold value for significant weather events or studied the climatology of the observation data Bischoff et al 2007 Chuda and Niino 2005 Craven and Brooks 2004 Derubertis 2006 Rasmussen et al 1998 Romero et al 2007 Wang et al 2000Although the annual precipitation in Korea is above the average annual precipitation in the world almost half of that precipitation discharges into the sea immediately after the rain because there are so many high mountains where the stream gradient is steep As a result Korea is one of the countries facing water shortage as determined by Population Action International PAI 2000 and is classified as a low water resources environment in the Water Poverty Index developed by the Centre for Ecology and Hydrology Centre for Ecology and Hydrology 2005 It is therefore necessary to find a fundamental solution to the water shortage problem in KoreaThe easiest method to resolve the water shortage problem is groundwater development or seawater desalination However limited groundwater resources and the economic feasibility of seawater desalination and the quality of obtained water are some of the problems associated with the application of the problems associated with these methods Most countries choose to solve their water shortage problems by means of artificial precipitation Seo 2001 Desert Research Institute in Reno Nevada USA has implemented a longterm program of cloud seeding operating 25–30 times a year spending US 614000 a year over 30 years In several states in the western USA programs for precipitation enhancement rainfall augmentation hail suppression and snowpack augmentation using cloud seeding are in the planning or operational stage Cloud–aerosol interaction and precipitation enhancement experiment in Hyderabad India plans to implement artificial rainfall experiments by 2010 investing 23 billion won for the last 5 years using hygroscopic flares and seeding Indian Institute of Tropical Meteorology 2009 China too has recently implemented artificial rainfall with silver iodide seeding using cannonballs rockets and howitzersThus cloud seeding is the most common method used worldwide for stimulating rainfall since its first implementation in 1946 However it is difficult to judge correctly how much of the rainfall after cloud seeding is induced artificially and what part was of natural origin AMS 1992 1998 Cotton 1986In this study we present a method for inducing artificial showery rain by means of ground heating In this method a heat source on the ground creates an ascending air current When this ascending air current overcomes the convective inhibition CIN in an unstable atmosphere showery rain is induced In spite of almost zero CIN if updrafts do not exist convective available potential energy CAPE at the upper level is not activated Therefore precipitation occurrence is not aided by the CIN value but by the formation either naturally or artificially of an updraft from the surface to the CAPE layer

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