西安对流层顶气象要素的特征分析

Characteristics of Meteorological Elements of Tropopause over Xi'an

利用1974—2012年西安高空气候资料月报表,分析对流层顶气象要素的年变化特征,采用线性倾向估计法分析对流层顶的气候趋势.结果表明:西安第Ⅰ对流层顶仅在11月至次年4月出现,第Ⅱ对流层顶则全年都有,复合对流层顶出现月份与第Ⅰ对流层顶一致;第Ⅰ对流层顶高度1月最低,其后逐月增加,第Ⅱ对流层顶5—8月高度较高,11月至次年2月高度较低;第Ⅱ对流层顶温度最低月与高度最高月相对应;10月至次年5月盛行西风,6月大幅向北偏转,7月盛行西北风,8月、9月向南回归,幅度较大;风速年内变化明显,11月至次年2月较大,2月后逐月减小,8月风速最小,8月后又逐月增大;38年以来,第Ⅰ对流层顶高度、温度变化趋势无论升降,均不显著;第Ⅱ对流层顶1—10月高度呈上升趋势,温度1月、4月升高,7月、10月下降.

Based on the monthly data （1974--2012） of Xi＇an＇s aeroclimate, the annual characteristics of meteorological elements of tropopause were analyzed and the linear trend estimation method was adopted to indicate the climatic trends of tropopause. The results show that the first tropopause only appears from November to April, which is consistent with the months when compound tropopuse appears, and the second tropopause exists all the year round. The height of the first tropopause is the lowest in January and then increases monthly, while the height of the second tropopause is higher from May to August and lower from November to February. The month with the lowest temperature corresponds with the month with maximum height of the second tropopause. Westerly wind is prevalent from October to May, then the wind begins to turn northwards in June and then comes from northwest in July. Afterwards,the wind comes from the south in August and September. The wind speed from November to February is higher and then decreases monthly until it reaches a minimum in August. After that, the wind speed increases monthly. Over the 38 years,the linear trends of both height and temperature of the first tropopause are not statistically significant,while the height of the second tropopause presents a rising trend from January to October,and the temperature rises in January and April and drops in July and October.