  Propagation effects are one of the main sources of noise in high-precision
pulsar timing. For pulsars below an ecliptic latitude of $5^\circ$, the ionised
plasma in the solar wind can introduce dispersive delays of order 100
microseconds around solar conjunction at an observing frequency of 300 MHz. A
common approach to mitigate this assumes a spherical solar wind with a
time-constant amplitude. However, this has been shown to be insufficient to
describe the solar wind. We present a linear, Gaussian-process piecewise
Bayesian approach to fit a spherical solar wind of time-variable amplitude,
which has been implemented in the pulsar software run_enterprise. Through
simulations, we find that the current EPTA+InPTA data combination is not
sensitive to such variations; however, solar wind variations will become
important in the near future with the addition of new InPTA data and data
collected with the low-frequency LOFAR telescope. We also compare our results
for different high-precision timing datasets (EPTA+InPTA, PPTA, and LOFAR) of
three millisecond pulsars (J0030$+$0451, J1022$+$1001, J2145$-$0450), and find
that the solar-wind amplitudes are generally consistent for any individual
pulsar, but they can vary from pulsar to pulsar. Finally, we compare our
results with those of an independent method on the same LOFAR data of the three
millisecond pulsars. We find that differences between the results of the two
methods can be mainly attributed to the modelling of dispersion variations in
the interstellar medium, rather than the solar wind modelling.
