A middle latitude Rayleigh-scatter lidar temperature climatology determined using an optimal estimation method

  • Jalali A
  • Sica R
  • Haefele A
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Abstract

<p><strong>Abstract.</strong> Hauchecorne and Chanin (1980) developed a robust method to calculate middle atmosphere temperature profiles using measurements from Rayleigh-scatter lidars. This traditional method has been successfully used to greatly improve our understanding of middle atmospheric dynamics, but the method has some shortcomings in regard to the calculation of systematic uncertainties and vertical resolution of the retrieval. Sica and Haefele (2015) have shown the Optimal Estimation Method (OEM) addresses these shortcomings and allows temperatures to be retrieved with confidence over a greater range of heights than the traditional method. We have developed a temperature climatology from Purple Crow Lidar (PCL) Rayleigh-scatter measurements on 519 nights using an OEM. Our OEM retrieval is a first-principle retrieval where the forward model is the lidar equation and the measurements are the level 0 count returns. It includes a quantitative determination of the top altitude of the retrieval, the evaluation of 9 systematic plus random uncertainties, and vertical resolution of the retrieval on a profile-by-profile basis. By using the calculated averaging kernels our new retrieval extends our original climatology by an additional 5 to 10<span class="thinspace"></span>km in altitude relative to the traditional method. The OEM statistical uncertainty makes the largest contribution in the uncertainty budget. However, significant contributions are also made from the systematic uncertainties, in particular the uncertainty due to choosing a <q>tie-on</q> pressure as required by the assumption of hydrostatic equilibrium, mean molecular mass variations with height, and ozone absorption cross section uncertainty. The vertical resolution of the PCL climatology is 1<span class="thinspace"></span>km up to about 90<span class="thinspace"></span>km and then increases to about 3<span class="thinspace"></span>km around 100<span class="thinspace"></span>km. The new PCL temperature climatology is compared with three sodium lidar climatologies. The comparison between the PCL and sodium lidar climatologies shows improved agreement relative to the climatology generated using the method of Hauchecorne and Chanin, that is the PCL climatology is as similar to the sodium lidar climatologies as the sodium lidar climatologies are to each other. The height-extended OEM-derived climatology is highly insensitive to the choice of an <i>a priori</i> temperature profile, in the sense that the <i>a priori</i> temperature profile contributes much less uncertainty than the statistical uncertainty.</p>

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Jalali, A., Sica, R. J., & Haefele, A. (2018). A middle latitude Rayleigh-scatter lidar temperature climatology determined using an optimal estimation method. Atmospheric Measurement Techniques Discussions, 1–24. https://doi.org/10.5194/amt-2018-117

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