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We have used solar oscillation frequencies and frequency splittings obtainedover solar cycles 23 and 24 to investigate whether the base of the solarconvection zone shows any departure from spherical symmetry. We used theeven-order splitting coefficients, $a_2$-$a_8$, and estimated the contributionsfrom each one separately. The average asphericity over the two solar cycles wasdetermined using frequencies and splittings obtained with a 9216-daytime-series. We find that evidence of asphericity is, {\em at best}, marginal:the $a_2$ component is consistent with no asphericity, the $a_4$ and $a_6$components yield results at a level a little greater than $1\,\sigma$, whilethe $a_8$ component shows a signature below $1\,\sigma$. The combined resultsindicate that the time average of the departure from the spherically symmetricposition of the base of the convection zone is $\lesssim 0.0001R_\odot$. Wehave also used helioseismic data obtained from time-series of lengths 360 days,576 days, 1152 days, and 2304 days in order to examine the consistency of theresults and evaluate whether there is any time variation. We find that theevidence for time variation is statistically marginal in all cases, except forthe $a_6$ component, for which tests consistently yield $p$ values of less than$0.05$.

Asphericity of the base of the solar convection zone