Table 1 . Regression coefficients of the multiple regression
model (see equation 1), along with their standard deviations (1.5 or 2
or 3 standard deviations) for the NLC occurrence number and NLC
brightness for the period of 1968-2018. Corresponding confidence
probabilities (90% or 95% or 99%) are shown in brackets.
Statistically significant coefficients (equal to or greater than its
error) at the corresponding confidence levels are marked in bold. The
time regression coefficient (C1 ) is expressed in
value per year (V/yr), the solar regression coefficient
(C2 ) is expressed in value per solar flux unit
(SFU, 1011 photons cm-2s-1), the volcanic regression coefficient
(C3 ) is expressed in value per VEI (Value/VEI),C0 is the regression constant. Phase lags (years)
are introduced for the Lyman α flux and VEI. The P values for the null
hypothesis test have been calculated for each regression coefficient.
Table 1 represents three model runs with three different selections of
volcanic activity:
a) all volcanic eruptions that occurred around the world (all
VEI values, all longitudes and all latitudes);
b) volcanic eruptions with all VEI values at all longitudes and
at latitudes between 30°S and 30°N;
c) volcanic eruptions with VEI>=3 at all
longitudes and at latitudes between 30°S and 30°N.