The Relation between Space Charge and Potential Gradient
Misaki, M.
Abstract
It is often found that atmospheric space charge density alters well correspondingly potential gradient when they are observed at less than a few meters above the ground, From the results obtained at the Kakioka Magnetic Observatory. this correspondence is seen only when the values of potential gradient attain more than a few hundred volts per meter.
Diurnal variations of both elements in quiet days are much different each other. The observational relations between space charge and potential gradient is shown in Fig.6， in which it is obviously seen that space charge density tends to the suturated value of 0.4 - 0.5 statcoulomb/m3 when field increase sufficiently intense such that it exceeds 1000 - 1500 volt/meter.
It is considered at“electrode-effect" would play a important role in the correspondence of space charge to potential gradient. From the equations of ion-equilibrium (eqs. (1) - (4) ), space charge due to electrode-effect near the ground was calculated. In the course of the deduction，it is assumed that electrical condition is stationary， and that meteorological eddy diffusion can be ignored. Since the current of large ions(i , i ) can be neglected， field affects only small ions but large ions， forming space charge near the ground. Space charge which consists of small ions is given by eq. (28) or ρs-curve in Fig. 7 (in eq.(28)，the height: 1.5m above the ground).
The distribution of large ions should be determined by the ion-equilibrium law， that is， large ion density depends on small ion and nucleus numbers at the place where that large ions exist.
In sucn a way，large ions in addtion to small ions form the total space charge which is shown by ρs+l -curve in Fig. 7.
The vertical distribution of space charge that is formed by electrode-effect is given in Fig. 8
in the cases of E=l00 volt/meter and 1000 volt/meter， which sbows the steep decrement with height in a few meters above the ground.
Comparing Fig. 6 with 7， we can see that Ps-curve coincides with the observational results，but ρs+l -curve does not. It seems that turbulent motion of the air is likely to diffuse large ions and make their distribution uniform.
Owing to some unknown factors， so to speak“noise" , the points in Fig.6 are dispersed to some degree. Since the space charge resulted from electrode-effect. in week field such as at calm days， may be merged into this noise， space charge observed does not correspond apparently to potential gradient. When the field becomes more intense， however， the electrode-effect grows
predominant，and consequently， the variations of space charge behave corresponding to those of potential gradient.
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