واکاوی خصوصیات ابرها و برخی شاخص‌های فیزیکی موثر در بارش مشهد

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری، هواشناسی کشاورزی، دانشگاه فردوسی، مشهد، ایران

2 گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی، مشهد، ایران.

3 دانشیار، گروه آمارِ، دانشکده ریاضی، دانشگاه فردوسی، مشهد، ایران.

چکیده

نظر به اهمیت نوع، میزان و خصوصیات ابرناکی، همچنین نقش رطوبت و شرایط ناپایداری در فرایند بارش، تحقیق زیر برای واکاوی مشخصات ابرها در فصول مختلف سال و  بررسی برخی شاخص­های فیزیکی تأَثیرگذار بر بارش، انجام شد. به این منظور در ابتدا، اطلاعاتابرناکیشهر مشهد در دوره زمانی 2010-1986 از بانک اطلاعاتی اداره کل هواشناسی خراسان رضوی استخراج گردید.  مقدار ابرناکی، فراوانی رخداد ابرهای پایین، متوسط و فراوانی رخداد ابرهای با رشد قایم شامل ابرهای کومولوس نوع2 و کومولونیمبوس، در ماه­های مختلف سال مشخص شد. در بررسی خصوصیات فیزیکی ابرها، با توجه به نقش دمای ابر درفرایند بارش، با استفاده از نمودارهای جوبالای ایستگاه مشهد، در بازه زمانی 1992 تا 2011،  دمای پایه ابر در ماه­های مختلف مشخص گردید. سپس با توجه به اهمیت و  نقش شرایط ناپایداری و رطوبت جو، در ایجاد بارش به بررسی رابطه بین برخی شاخص­های ناپایداری، شامل شاخصCAPE  ، شاخص K، شاخصshowalter و شاخص آب قابل بارش، با میزان بارش پرداخته شد، در انتها با ایجاد یک معادله رگرسیونی، سهم هر کدام از این شاخص­ها در میزان بارش مشخص گردید. بررسی ها نشان داد که ارتباط برخی از شاخص­ها و لگاریتم بارش، بهصورت خطی نمی­باشد. اما، نتایج حاصل از تحلیل واریانس رگرسیون، نشان از معنی­دار بودن رگرسیون در سطح 99درصد داشت یعنی حداقل یکی از شاخص­های ناپایداری دارای رابطه خطی با لگاریتم طبیعی بارش شش ساعته است. مشخص شد که تنها ارتباط متغیرهای K و SI با لگاریتم طبیعی بارش در سطح اطمینان 95 درصد معنی­دار هستند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Exploring cloud's characteristics and some effective physical indices in Mashhad's precipitation

نویسندگان [English]

  • Mohsen Rahmdel 1
  • Seyed Hossein Sanaeinejad 2
  • Hadi Jabbari 3
1 PhD Student of Agricultural Meteorology, Ferdowsi University, Iran.
2 Assistant Professor, Faculty of Water Sciences Engineering, Ferdowsi University, Mashhad, Iran.
3 Assistant Professor, Faculty of Mathematics, Ferdowsi University, Mashhad, Iran.
چکیده [English]

The aim of this study was to investigate cloud’s characteristics and some effective physical indices on rainfall in Mashhad. We initially studied cloudy sky in Mashhad by consulting meteorological yearbook of 1986-2010. Density and prevalence for medium and low clouds as well as density, prevalence and average for vertical clouds (type 2 cumulus and cumulonimbus) were calculated for every month. This study shows that in Mashhad the highest frequency of low and medium clouds occurs in cold and rainy months during winter and spring, while most of the clouds with vertical development occur in spring. We also studied freezing level in clouds in both rainfall and no-rainfall cases, using skew-T diagrams and radiosonde data during 1992 to 2011. The condition considered here was overcast sky. We obtained a regression equation in order to specify role of physical indices (CAPE، SI, K، PWT) in precipitation. At first, rainfall days of Mashhad were extracted from Khorasan Razavi meteorological department archive (1992 to 2011). On these days, six hour rainfall (00 to 06 Z) were determined. Then, instability and physical indices were obtained from radiosonde data of Mashhad weather station. A regression equation was estimated by analyzing the relationship between natural logarithm of six-hour rainfall as dependent variable and instability indices as independent variable. This research determines which relationship between some indices with natural logarithm of six-hour rainfall is nonlinear. Analysis of regression variance shows that regression was significant at 99% level. This means that at least one of the indices has a linear relationship with logarithm of six-hour rainfall. In this equation, due to significant level, CAPE and PWT were removed. Most relationships were found between SI and natural logarithm of six-hour rainfall.

کلیدواژه‌ها [English]

  • CAPE Index
  • K index
  • Precipitable Water Index
  • Showalter Index
  • Skew-T diagram
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