Observing crosswind over urban terrain using scintillometer and Doppler lidar

• Main Authors: D. van Dinther, C. R. Wood, O. K. Hartogensis, A. Nordbo, E. J. O'Connor
• Format: Article
• Language: English
• Published: Copernicus Publications 2015-04-01
• Series: Atmospheric Measurement Techniques
• Online Access: http://www.atmos-meas-tech.net/8/1901/2015/amt-8-1901-2015.pdf

In this study, the crosswind (wind component perpendicular to a path, <i>U</i>_&bot;) is measured by a scintillometer and estimated with Doppler lidar above the urban environment of Helsinki, Finland, for 15 days. The scintillometer allows acquisition of a path-averaged value of <i>U</i>_&bot; (<span style="border-top: 1px solid #000; color: #000;"><i>U</i>_&bot;</span>), while the lidar allows acquisition of path-resolved <i>U</i>_&bot; (<i>U</i>_&bot; (<i>x</i>), where <i>x</i> is the position along the path). The goal of this study is to evaluate the performance of scintillometer <span style="border-top: 1px solid #000; color: #000;"><i>U</i>_&bot;</span> estimates for conditions under which <i>U</i>_&bot; (<i>x</i>) is variable. Two methods are applied to estimate <span style="border-top: 1px solid #000; color: #000;"><i>U</i>_&bot;</span> from the scintillometer signal: the cumulative-spectrum method (relies on scintillation spectra) and the look-up-table method (relies on time-lagged correlation functions). The values of <span style="border-top: 1px solid #000; color: #000;"><i>U</i>_&bot;</span> of both methods compare well with the lidar estimates, with root-mean-square deviations of 0.71 and 0.73 m s^&minus;1. This indicates that, given the data treatment applied in this study, both measurement technologies are able to obtain estimates of <span style="border-top: 1px solid #000; color: #000;"><i>U</i>_&bot;</span> in the complex urban environment. The detailed investigation of four cases indicates that the cumulative-spectrum method is less susceptible to a variable <i>U</i>_&bot; (<i>x</i>) than the look-up-table method. However, the look-up-table method can be adjusted to improve its capabilities for estimating <span style="border-top: 1px solid #000; color: #000;"><i>U</i>_&bot;</span> under conditions under for which <i>U</i>_&bot; (<i>x</i>) is variable.