vernal equinox
spring equinox

This differs from the solar or tropical year which has length equal to the time interval between vernal equinoxes in successive years.

Conversely, Dakshinaya is defined as the period between the Autumnal and Vernal Equinoxes, when there is midnight sun at the South Pole.

Although this is closer to the mean tropical year of 365.24219 days, his proposal has never been adopted because the Gregorian calendar is based on the mean time between vernal equinoxes (currently 365.2424 days).