Tropospheric water vapor profiles obtained with FTIR: comparison with balloon-borne frost point hygrometers and influence on trace gas retrievals
Tropospheric water vapor profiles obtained with FTIR: comparison with balloon-borne frost point hygrometers and influence on trace gas retrievals
复制标题
DOI：
10.5194/amt-12-873-2019
复制
发表时间：
2018-10
影响因子：
3.8
通讯作者：
I. Ortega;R. Buchholz;E. Hall;D. Hurst;A. Jordan;J. Hannigan
中科院分区：
文献类型：
--
作者：
I. Ortega;R. Buchholz;E. Hall;D. Hurst;A. Jordan;J. Hannigan
抽象。关键大气气体垂直剖面的反演提供了地面傅里叶变换红外线太阳吸收测量的关键长期记录。然而，检索的垂直剖面结构的表征可能难以验证，特别是对于具有大的垂直梯度和时空变化的气体，如水蒸气。在这项工作中，我们评估的准确性最常见的水蒸气同位素（H216 O，以下WV）傅立叶变换红外光谱反演在较低和较高的对流层低平流层。2010年至2016年，使用气球携带的NOAA霜点湿度计（FPH）获得的高质量垂直分辨WV剖面测量值被用作参考，以评估两个站点检索剖面的性能：科罗拉多的博尔德（BLD）和夏威夷的莫纳罗亚（MLO）山顶天文台。为了进行有意义的比较，时空变异性进行了研究。我们提出了FTIR检索与未平滑和平滑FPH配置文件之间的比较结果，以评估WV垂直梯度。此外，我们评估的定量影响不同的先验配置文件中检索的WV。正交线性回归分析表明，使用ERA-Interim（ERA-I）的先验配置文件和偏差之间的对流层层的最佳相关性较低的非平滑比较。在博尔德，我们发现1.5-3 km层的负偏差为0.02± 1.9%（r=0.95）。在3-5 km的自由对流层低层中，由于WV的垂直变化较快，反演结果不一定能捕捉到WV的垂直变化，因此存在较大的负偏差（11.1± 3.5%）（r=0.97）。在5- 7.5km层，偏差得到改善（1.0± 5.3%，r=0.94）。对于7.5 km以上但13.5 km以下的地层，偏差保持在约13%。在MLO处，由于探测器的发射距离FTIR位置更远，空间失配明显更大。然而，我们估计3.5-5.5 km层的负偏差为5.9± 4.6%（r=0.93），5.5-7.5 km层的负偏差为9.9± 3.7%（r=0.93），我们测量7.5-10 km层的正偏差为6.2± 3.6%（r=0.95），10 km以上的正偏差为12.6%或更大。第一层的一致性在BLD下明显更好，因为FTIR和FPH的空气质量相似。此外，第一次，我们研究了不同的WV先验配置文件在检索选定的气体配置文件的影响。使用NDACC标准检索，我们目前的结果为氰化氢（HCN），一氧化碳（CO），乙烷（C2 H6）的NOAA FPH配置文件作为地面真相和其他WV配置文件的影响进行评估。我们表明，在所有垂直层中，C2 H6的影响较小（所有WV源的偏差<0.5%）。然而，对于HCN，我们发现显着的偏差之间的6%的层接近地面和2%的对流层上部取决于WV的轮廓源。对于预检索的WV，总是找到最佳结果（降低的偏差和精度以及r值更接近1）。因此，我们建议首先检索WV，以用于后续的气体检索。
Abstract. Retrievals of vertical profiles of key atmospheric gases provide a critical long-term record from ground-based Fourier transform infrared (FTIR) solar absorption measurements. However, the characterization of the retrieved vertical profile structure can be difficult to validate, especially for gases with large vertical gradients and spatial–temporal variability such as water vapor. In this work, we evaluate the accuracy of the most common water vapor isotope (H216O, hereafter WV) FTIR retrievals in the lower and upper troposphere–lower stratosphere. Coincident high-quality vertically resolved WV profile measurements obtained from 2010 to 2016 with balloon-borne NOAA frost point hygrometers (FPHs) are used as reference to evaluate the performance of the retrieved profiles at two sites: Boulder (BLD), Colorado, and at the mountaintop observatory of Mauna Loa (MLO), Hawaii. For a meaningful comparison, the spatial–temporal variability has been investigated. We present results of comparisons among FTIR retrievals with unsmoothed and smoothed FPH profiles to assess WV vertical gradients. Additionally, we evaluate the quantitative impact of different a priori profiles in the retrieval of WV. An orthogonal linear regression analysis shows the best correlation among tropospheric layers using ERA-Interim (ERA-I) a priori profiles and biases are lower for unsmoothed comparisons. In Boulder, we found a negative bias of 0.02±1.9 % (r=0.95) for the 1.5–3 km layer. A larger negative bias of 11.1±3.5 % (r=0.97) was found in the lower free troposphere layer of 3–5 km attributed to rapid vertical change of WV, which is not always captured by the retrievals. The bias improves in the 5–7.5 km layer (1.0±5.3 %, r=0.94). The bias remains at about 13 % for layers above 7.5 km but below 13.5 km. At MLO the spatial mismatch is significantly larger due to the launch of the sonde being farther from the FTIR location. Nevertheless, we estimate a negative bias of 5.9±4.6 % (r=0.93) for the 3.5–5.5 km layer and 9.9±3.7 % (r=0.93) for the 5.5–7.5 km layer, and we measure positive biases of 6.2±3.6 % (r=0.95) for the 7.5–10 km layer and 12.6 % and greater values above 10 km. The agreement for the first layer is significantly better at BLD because the air masses are similar for both FTIR and FPH. Furthermore, for the first time we study the influence of different WV a priori profiles in the retrieval of selected gas profiles. Using NDACC standard retrievals we present results for hydrogen cyanide (HCN), carbon monoxide (CO), and ethane (C2H6) by taking NOAA FPH profiles as the ground truth and evaluating the impact of other WV profiles. We show that the effect is minor for C2H6 (bias <0.5 % for all WV sources) among all vertical layers. However, for HCN we found significant biases between 6 % for layers close to the surface and 2 % for the upper troposphere depending on the WV profile source. The best results (reduced bias and precision and r values closer to unity) are always found for pre-retrieved WV. Therefore, we recommend first retrieving WV to use in subsequent retrieval of gases.