3. The τ Dependences on the Solar Wind Velocity and the Spectrum of Particles
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Figure 1
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[10] An ideal verification of the correctness of formula (1) would be
the invariance of the value of the right hand part of (1) with
current values of
r,
V, and
γ during the whole decay. But the
construction of the "time profile" described by (1) cannot be
realized in practice. Thus, to investigate the correspondence of
formula (1) to the observed tendencies in the behavior of
τ as a
function of
V and
γ, we have chosen from the total amount of
decays only those events for which the solar wind speed
V was
constant (within 5%) and which allowed to determine the index
γ of the energy spectrum (the value of
γ was determined at the
beginning of the exponential decay). We found 52 such decays.
The relation between the measured value of
τ,
τ exp, and the value
of
τ theor,
calculated from formula (1) is presented in Figure 1.
Despite the significant scatter of points, one can see that
approximately one half of the events is described by this
formula quite satisfactorily (26 declines with accuracy
<25 %
and 17 declines with accuracy 25-50%). It is worth noting, that
the overwhelming majority (9 out of 13) events with
τ exp >τ theor beyond the limits of the accuracy of 25%, correspond to values
of the solar wind velocity
>400 km s-1.
On the contrary, the
majority (10 out of 13) events with
τ exp <τ theor correspond to
<400 km s-1.
This effect can be partly related to the changes of
γ during the decline. According to (1), if the spectrum during the
decay becomes harder ( γ diminishes)
τ should increase and vice
versa. However, the periods of decays with
V= const were not
sufficiently long (between 12 and 50 hours) that changes in the
spectrum exponent could play a significant role in the changes
of
τ.
[11] On the other hand, it can mean that approximately one half of
the solar events does not satisfy simultaneously all the accepted
criteria: events have a more complicated character (the outcome
of particles is not pulsed, acceleration takes place not on the Sun
but at the lower values of
r, particle fluxes are not large enough,
the background fluxes cannot be estimated accurately, etc.).
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