Campbell Scientific CS110 Overview - Manual (Page 2)

The electric field E is a vector quantity, having
both a magnitude (field strength) and direction
(direction of force exerted on a positive test
charge). The units of electric field are Newtons/
Coulomb, which are equivalent to the more
commonly expressed units of Volt/meter (V/m).
The magnitude of the electric field is equivalent
to the potential (voltage) gradient.
Because large quantities of separated electrical
charges are associated with thunderstorms, the
vertical component of atmospheric electric field
E at the earth’s surface is useful for studying
electrified clouds and for lightning warning.
By convention, the sign of the electric field is
considered positive (positive test charge would
be pulled upward) if the overhead charge is pre-
dominantly negative, and defined as negative
(positive test charge would move downward) if
overhead charge is predominantly positive.
On a clear day (fair weather), a relatively small
number of positive ions exist in the atmosphere
that give rise to an electric field on the order of
-100 to -200 V/m. These fair weather ions are
thought to be generated by means of world-
wide thunderstorms and distributed globally by
the conductive electrosphere. The local electric
field during a 24 hour fair weather period as
measured with a CS110 electric-field meter is
illustrated in Figure. 2.
Figure 1. Sign convention of electric field at the Earth’s surface.
(a) Positive electric field induced by negative charge at the cloud base.
(b) Negative electric field induced by positive ions in the fair weather conditions.
Figure 2. Electric-Field Measured with CS110 During 24 Hour Period of Fair Weather.
Electrifi ed Cloud
Fair Weather
Electric Field
Solar Radiation
Mountain Daylight Time (1 minute average of 1 second samples)
Electric Field (volt/meter)
Diurnal Fair Weather Electric Field at Logan, Utah on July 27, 2005
(Mean Value =-75.1 Volt/meter, Mean Temperature = 68.8ºF)
Solar Radiation (W
atts per square meter)
2