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Propagation effects are one of the main sources of noise in high-precisionpulsar timing. For pulsars below an ecliptic latitude of $5^\circ$, the ionisedplasma in the solar wind can introduce dispersive delays of order 100microseconds around solar conjunction at an observing frequency of 300 MHz. Acommon approach to mitigate this assumes a spherical solar wind with atime-constant amplitude. However, this has been shown to be insufficient todescribe the solar wind. We present a linear, Gaussian-process piecewiseBayesian approach to fit a spherical solar wind of time-variable amplitude,which has been implemented in the pulsar software run_enterprise. Throughsimulations, we find that the current EPTA+InPTA data combination is notsensitive to such variations; however, solar wind variations will becomeimportant in the near future with the addition of new InPTA data and datacollected with the low-frequency LOFAR telescope. We also compare our resultsfor different high-precision timing datasets (EPTA+InPTA, PPTA, and LOFAR) ofthree millisecond pulsars (J0030$+$0451, J1022$+$1001, J2145$-$0450), and findthat the solar-wind amplitudes are generally consistent for any individualpulsar, but they can vary from pulsar to pulsar. Finally, we compare ourresults with those of an independent method on the same LOFAR data of the threemillisecond pulsars. We find that differences between the results of the twomethods can be mainly attributed to the modelling of dispersion variations inthe interstellar medium, rather than the solar wind modelling.

A Gaussian-processes approach to fitting for time-variable spherical solar wind in pulsar timing data