Measuring Meteorology in Urban Areas – Some Progress and Many Problems - Meteorological and Air Quality Models for Urban Areas - page 112

Chapter 12
Measuring Meteorology in Urban Areas - Some
Progress and Many Problems

Sven-Erik Gryning and Ekaterina Batchvarova

Abstract Examples of the use of remote sensing with relevance for the urban
boundary layer are presented as an inspiration for future observational studies in
urban areas. The examples, involve the measurement of: the vertical wind profile
and horizontal variability of the mean wind speed over a forest; and the depth of
the marine boundary layer. Research radio-soundings are an indispensable tool in
observational campaigns.

12.1 Introduction

The temporal and spatial variability of meteorological measurements inside the
boundary layer constitute major obstacles in the interpretation of the observations.
In numerical models properties are averaged over the grid cells; however, grid cells
usually cover several types of terrain. Turbulence and wind interact in a non-linear
way to changes in the underlying surface (Batchvarova et al., 2001), consequently
even over seemingly homogeneous terrain variations in the turbulence can be con-
siderable. Despite these fundamental difficulties in the interpretation of measure-
ments, the thrust of experimental research in the field of boundary layer meteorology
has been fuelled by point measurements.
Following Batchvarova and Gryning (2006) Fig. 12.1 shows a schematic sketch
of a slice of an urban area with indication of the scales and their regimes. It looks
complicated but nevertheless constitutes a considerable simplification. The rough-
ness sub-layer (Fig. 12.1) is complicated as the turbulence varies in space and time
in an erratic manner. The dispersive stress, being the transport of momentum by
spatial fluctuations, is considerable and is expected to be larger when the rough-
ness elements have non-uniform sizes. It increases towards the ground which can be