A technique
to detect
microclimatic inhomogeneities in historical records of screen-level air
temperature
Runnalls K. E.
and T. R. Oke
JOURNAL OF
CLIMATE 19 (6):
959-978 MAR 15 2006
Abstract: A
new method to detect errors or biases in screen-level air temperature
records
at standard climate stations is developed and applied. It differs from
other
methods by being able to detect microclimatic inhomogeneities in time
series.
Such effects, often quite subtle, are due to alterations in the
immediate
environment of the station such as change,, of vegetation, development
(buildings, paving), irrigation, cropping, and even in the maintenance
of the
site and its instruments. In essence, the technique recognizes two
facts:
differences of thermal microclimate are enhanced at night, and taking
the ratio
of the nocturnal cooling at a pair of neighboring stations nullifies
thermal
changes that occur at larger-than-microclimatic scales. Such ratios are
shown
to be relatively insensitive to weather conditions. After transforming
the time
series using Hurst resealing, which identifies long-term persistence in
geophysical phenomena, cooling ratio records show distinct
discontinuities,
which, when compared against detailed station metadata records, are
found to
correspond to even minor changes in the station environment. Effects
detected
by this method are shown to escape detection by Current generally
accepted
techniques. The existence of these microclimatic effects ire a source
of
uncertainty in long-term temperature records, which is in addition to
those
presently recognized such as local and mesoscale urban development,
deforestation, and irrigation.