Abstract:

With micro-pulse lidar (MPL) data, the max mixing height (MMH) in the summer of Naqu is retrieved by gradient method. With radiosonde data (twice daily at 08:00 and 20:00) and max potential temperature of Naqu in the corresponding date, MMH is retrieved by parcel method. The intercomparison between MMHs from the different data shows that the result from 08:00 radiosonde data consists well with MPL results, with correlation coefficient 0.85, root-mean-square error (RMSE) 0.30 km, mean absolute error (MAE) 0.25 km, and the t-test (0.95) passed. But the result from 20:00 radiosonde data has larger deviation from MPL results, with the correlation coefficient 0.84, RMSE 0.67 km, MAE 0.54 km and failed in the t-test. Deviation analysis shows that some factors such as the residual mixing layer in 20:00 soundings, some local weather process before the 20:00 launch time and the temporal-spatial variation of the mixing height induced by the thermal convective bubbles or/and the entrainment process may cause the inconsistency in the results. All above lead to the non-availability of the 20:00 radiosonde data in retrieving the mixing height. The character of the diurnal variation of the potential temperature profile will also affect the accuracy of retrieval result, which would produce a higher height from 08:00 data, and some statistical corrections should be used to improve the result.

Key words: Tibetan Plateau, max mixing height, micro-pulse lidar, radiaosonde data

摘要：

利用微脉冲激光雷达探测资料, 采用梯度法获取那曲地区夏季的混合层高度序列及日最大混合层高度; 利用每日两次(08:00 和 20:00)的探空资料结合地面最大位温, 采用气块法得到雷达探测对应日期的日最大混合层高度(MMH)。通过对比从不同资料得到的 MMH, 发现 08:00 探空反演结果与激光雷达结果有较好的一致性(相关系数R为0.85, 均方根误差RMSE为0.30 km, 平均绝对误差 MAE 为 0.25 km, 并通过显著性水平为 0.95 的 t 检验); 20:00探空反演结果则与激光雷达结果偏差相对较大(R 为 0.84, RMSE 为 0.67 km, MAE为0.54 km, 未通过 t 检验)。分析产生偏差的原因发现, 探空时刻的残余层、前期的天气变化过程以及对流泡活动或强卷夹过程引起的混合层高度时空变化等都可能是导致20:00高度结果与激光雷达结果不一致的原因, 使得 20:00 探空资料不适合进行最大混合高度的反演。位温廓线的日变化特征也会影响反演结果的准确性, 导致08:00探空结果偏高, 但可以通过统计订正做修正。

关键词: 青藏高原, 最大混合高度, 微脉冲激光雷达, 常规探空