Atmospheric electrostatics. wahlin l. chapter 7

CHAPTER 7
RESULTS OF FAIR-WEATHER MEASUREMENTS
7.1 THE COLORADO MEASUREMENTS
The work presented in this chapter is based on atmospheric electric
And meteorological data continuously recorded over a two year period
Using instrumentation and measuring methods descried in the previous
Chapters of this book. Evaluation of the data suggests that the fairweather
Electric field is primarily generated by local electrostatic
Generators which all contribute to a larger global circuit. The main
Generating mechanism appears to be linked to convective mixing
Processes in the atmosphere. The amount of charge contributed to the
Global electric circuit by local thunderstorms could not be determined
From the measurements. Since convective mixing is more dominant
Over land than sea one can expect a small global diurnal increase in the
Fairweather field produced by static electricity generated over land
Masses as the sun passes over different world continents. Such global
Variations were observed in Lappland by Simpson in 1905 and from
Ocean measurements by Hoffman in 1923. The diurnal variations of
The fairweather electric field in Boulder is compared to Hoffman’s
Ocean results.
The use of digital storage and evaluation technology has made it
Possible to study atmospheric electric phenomena in great detail.
Meteorological and atmospheric electric parameters have been
Continuously monitored at Colutron Research in Boulder Colorado
Over several years. Boulder is located at latitude 40° N and longitude
110 ATMOSPHERIC ELECTROSTATICS
105° W and at an altitude of about 1500 m above sea level. The
Different parameters recorded are electric field, air-earth current
Density, negative and positive ion concentrations, relative
Humidity, temperature, wind velocity, and barometric pressure.
Readings are

taken every 30 second and stored on magnetic disks. The
Measurements are performed at ground level. In this study only
Data from undisturbed fairweather days were selected, i. e. cloudless
Days without disturbances from frost, dew, blowing dust etc. The
Average of “hourly means” from any chosen number of fairweather
Days is examined for diurnal variation patterns. The curves in
Fig. 49 show an example of electric measurements for sixteen fairweather
Days in December 1990.
Fig. 49. Diurnal variations of electric field, ion current and ion
Density from 16 fairweather days in Dec. 1990.
7.2. MEASURING TECHNIQUES
Electric field is obtained by measuring the potential on a 5 m long
Wire suspended horizontally one meter above ground. A radioactive
FAIRWEATHER MEASURMENTS 111
Source (Po 220) attached to the wire assures good electric
Conduction to the surrounding air. Air to earth current is collected
On an electrically insulated one square meter copper plate situated at
The earth’s surface. Gerdien ion counters record positive and negative
Ion densities in the atmosphere. The ion density, which is proportional
To the conductivity of the atmosphere, is responsible for the air to earth
Leakage current. Relative humidity, temperature, wind velocity and
Barometric pressure are measured by conventional methods.
7.3. RELIABILITY OF MEASUREMENTS
Since the atmospheric electric parameters obey Ohm’s law (Wåhlin,
1992). it is possible to test the reliability of the measurements by
Simply comparing the recorded ion concentrations to the calculated ion
Concentrations obtained from the recorded electric field and current
Density data or
(n n ) i,
Eq q
+ + – = m =
L
M (16)


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Atmospheric electrostatics. wahlin l. chapter 7