Scintillometry in urban and complex environments: a review

Abstract

Knowledge of turbulent exchange in complex environments is relevant to a wide range of hydrometeorological applications. Observations are required to improve understanding and inform model parameterisations but the very nature of complex environments presents challenges for measurements. Scintillometry offers several advantages as a technique for providing spatiallyintegrated turbulence data (structure parameters and fluxes), particularly in areas that would be impracticable to monitor using eddy covariance, such as across a valley, above a city or over heterogeneous landscapes. Despite much of scintillometry theory assuming flat, homogeneous surfaces and ideal conditions, over the last 20 years scintillometers have been deployed in increasingly complex locations, including urban and mountainous areas. This review draws together fundamental and applied research in complex environments, to assess what has been learnt, summarise the stateof-the-art and identify key areas for future research. Particular attention is given to evidence, or relative lack thereof, of the impact of complex environments on scintillometer data. Practical and theoretical considerations to account for the effects of complexity are discussed, with the aim of developing measurement capability towards more reliable and accurate observations in future. The usefulness of structure parameter measurements (in addition to fluxes, which must be derived using similarity theory) should not be overlooked, particularly when comparing or combining scintillometry with other measurement techniques and model simulations.

Variability of urban surface temperatures and implications for aerodynamic energy exchange in unstable conditions

“…This uncertainty comes from a combination of sources, including systematic and random sensor errors, vertical flux divergence and lack of energy balance closure. Scintillometers in complex areas such as central London have typical uncertainty on the order of 20% due to variable meteorological inputs, surface conditions, instrument height and surface layer similarity theory assumptions (Crawford et al ., ; Ward, ).…”

Surface-Energy-Balance Closure over Land: A Review

“…However, these instruments do not measure the heat flux directly and are only sensitive to a part of the turbulence spectrum, i.e. the inertial subrange, and they rely on the validity of Monin-Obukhov similarity theory in order to determine fluxes from the measured structure parameters with all its implicit assumptions (Ward 2017). The underlying similarity functions have been determined from tower-based EC measurements and therefore are not disconnected from the energy balance closure problem.…”

Integrating thermal stress indexes within Shuttleworth–Wallace model for evapotranspiration mapping over a complex surface

“…However, the applicability of MOST is limited when conditions are not favorable, which can happen for a number of reasons. Atmospheric conditions, instrumental setup, data processing and evaluation criteria (particularly choice of similarity function and variable of interest) can all affect the MOST applicability (Ward 2017).…”