A320 Captain reported an intermittent fumes event described as a 'dirty socks' odor that dissipated and returned during troubleshooting and while flying in and out of clouds. Fumes remained constant from approach descent to arrival gate.

Narrative

Fumes began on ground APU Bleed on; Packs on during ZZZ turn after heavy rain rolled through airport. Strong musty; oily; dirty sock smell throughout cabin. We opened cockpit windows to dissipate feeling it was the typical moisture related temporary dirty sock smell when introduced to packs. However; smell persisted to cruise altitude (APU bleed was used for takeoff but turned off with After Takeoff Checklist) when we called to aft cabin to verify with inflight if still experiencing. Inflight said odor was no longer evident; but the odor remained strong in flight deck as we decided to run the supplemental checklist to isolate using oxygen masks for 3-5 minute pack 1; pack 2 isolation periods. We encountered moisture related weather for the first hour of flight in and out of clouds just before executing the checklist as we entered clear air. We assessed the fume odor event was isolated to pack 2 after conducting checklist; odor dissipated. However; we also correlated the dissipation with the probability we exited the clouds and moisture being introduced to the packs. We therefore elected to return to both packs operation and did not encounter the odor until descent passing FL180 all the way till taxi in requiring us to ventilate the cockpit upon parking by opening the windows. Inflight also reported the odor upon descent in the cabin. We attempted to isolate on decent with packs but it made no difference; pack 1 or pack 2; the odor remaining strong.