According to the TEPCO press release on March 20th, the only event I could find is the cooling of the spent fuel of reactor 2:
Cooling of Spent FuelFrom 3: 05 PM to 5: 20 PM on March 20th, 40 tons of seawater was injected into Unit 2 by TEPCO employees.
On the 22th, at 21:00 JST on March 22, there is a drop, that coincides with a westerly wind. Then the dose rate goes up as the winds comes back to the Ibakari region. So it looks like from the information currently available, the cooling of the pool in reactor 2 and attendant vapor generation might be responsible for this increase in dose rate in Ibakari.