Observing crosswind over urban terrain using scintillometer and Doppler lidar

Abstract. In this study, the crosswind (wind component perpendicular to a path, U_⊥) 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 U_⊥ (U_⊥), while the lidar allows acquisition of path-resolved U_⊥ (U_⊥ (x), where x is the position along the path). The goal of this study is to evaluate the performance of scintillometer U_⊥ estimates for conditions under which U_⊥ (x) is variable. Two methods are applied to estimate U_⊥ 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 U_⊥ of both methods compare well with the lidar estimates, with root-mean-square deviations of 0.71 and 0.73 m s⁻¹. This indicates that, given the data treatment applied in this study, both measurement technologies are able to obtain estimates of U_⊥ in the complex urban environment. The detailed investigation of four cases indicates that the cumulative-spectrum method is less susceptible to a variable U_⊥ (x) than the look-up-table method. However, the look-up-table method can be adjusted to improve its capabilities for estimating U_⊥ under conditions under for which U_⊥ (x) is variable.