The Potential of Rainfall for the Cloud Seeding Operations based on Instability Indices Foroozan Arkian * Meteorology Department, Marine Science and Technology Faculty, Tehran North Branch, Islamic Azad University, Iran * Corresponding author: Foroozan Arkian, Meteorology Department, Marine Science and Technology Faculty, Tehran North Branch, Islamic Azad University, Iran, Tel: +989125805886; E-mail: f.arkian@gmail.com Received date: May 13, 2016; Accepted date: Jul 22, 2016; Published date: Jul 29, 2016 Copyright: © 2016 Arkian F. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abstract Instability indices are the parameters that could be used to determine instability in the different parts of the atmosphere. In this study, we have used some of the indices to determine the probability of rainfall for cloud seeding operation in Mashhad region of Iran during (1993-2010). Used indices are including Precipitation Water of Cloud (PWC), Showalter Index (SI), K Index (KI) and Convective Available Potential Energy (CAPE). The optimal threshold of specific index for cloud seeding decision has been estimated using the best fitted curve on scattering diagram of the rainfall data and the index data. The optimal thresholds of PWC, SI and KI for convective cloud seeding activities were found 10 mm, 2°C and 24°C, respectively. The results show that rainfall could be occur with different amount of CAPE, even zero. Therefore, we could not consider any threshold for this index. The rainfall increase with increasing PWC, KI and CAPE; and decreasing SI in the region. Keywords: Cloud seeding; Potential of rainfall; Instability indices; Radiosonde Introduction Termodynamic diagrams are used in Practical and daily work of meteorologists as an auxiliary instruments to calculate the various quantities that cannot Measure by radiosonde. Some of those quantities such as Precipitation Water of Cloud (PWC), K Index (KI), Showalter (SI), Total (TT) and Convective Available Potential Energy (CAPE), determine the instability in atmosphere. Tese instability geneses are pronounced at the convection growth stage of clouds and linked closely to rainfall. Consequently, we can fnd a threshold for each instability indices that represent the potential of rainfall in specifc cloud. In this study, to determine the rainfall potential of clouds for cloud seeding operation, some of those instability indices including PWC, KI, SI and CAPE were calculated during rainy days of 1991-2002 years in Mashhad city of Iran. Te main goal of this article is to determine the optimal threshold for each index which shows minimum potential rainfall in cloud before seeding in the region. We’ve used best ftted curve on rainfall and the indices data to fnd optimal threshold [1-3]. Instability indices are calculated in some convective cloud seeding projects. Te rainfall augmentation for crops experiment (PACE) carried successfully [4], the PWC index and buoyancy potential (diference between environment temperature and parcel temperature in 500 mb) were determined as suitable factors in cloud seeding and PWC for 26 mm was found to be the optimal PWC threshold in conducting convective cloud seeding activities. Instability indices have been calculated through studying severe wind hail storm over Sofa, Bulgaria to obtain the seeding threshold and hail suppression [5-8]. In this study CAPE was found to be 3785 Jkg -1 , the vertical wind velocity of 21.9 m sec -1 and PWC of 12.9 Jkg -1 . Te some studies about a climate-related increase in extreme weather events have been done biased on instability indices [5,8-14]. Tunderstorm over Venice of Italy has been studied to fnd the most suitable forecast indices [12]. Some instability indices during hail suppression over Alberta, Canada, employing the cloud seeding operations on hailstorm [11]. Te indices were as follows: the average PWC (18.8 mm), Showalter index (-3°C) and set of sets index (TT) (54°C) convective available Potential Energy (781 Jkg -1 ). Chi and Leng provides valuable information to help pinpoint the likely locations for possible heavy rainfall occurrences. Te result shows that for the development of heavy rainfall, a deep warm, moist layer (high KI) is required but high CAPE may not be needed. Te surface-based lifed index is the most useful stability index for predicting convective development. Daily sounding-derived atmospheric stability indices are typically employed for short-term severe weather forecasts. Material and Methods In this study, some of the historic meteorological data during 1993-2010 are used. Te number of rainy days was 804, a day being classed as rainy if only hundredth of an inch of rain fell during the 24 h. Te dataset contains four sounding-derived parameters including PWC, SI, KI and CAPE at 1200 UTC formal sounding. To determine the optimal threshold for each index which shows minimum potential rainfall in cloud, the best ftted curve on scattering diagram of the rainfall data and the specifc index data are used. Also, the probability of the rainfall for diferent range of each index has been calculated. Mashhad city has a steppe climate with warm summers and cold winters and low precipitation. Almost all precipitation falls during the winter and during early spring. Figure 1 shows the location of Mashhad city in North East of Iran. Arkian, J Climatol Weather Forecasting 2016, 4:2 DOI: 10.4172/2332-2594.1000170 Research Article Open Access J Climatol Weather Forecasting, an open access journal ISSN:2332-2594 Volume 4 • Issue 2 • 1000170 Journal of Climatology & Weather Forecasting J o u r n a l o f C l i m a t o l o g y & W e a t h e r F o r e c a s t i n g ISSN: 2332-2594