Is this only applicable to contingencies in the Northern Hemisphere (South ascend North descend - SAND) Should we descend towards the South pole in the Southern Hemisphere?

Just follow the tropopause.

Gets higher towards the equator and lower towards the poles -> climb if turning towards the equator, descend if turning towards the poles.

Who's descending down whose pole?

I don't understand the question...

Should be weather deviation in oceanic airspace > contingency.

Just follow the tropopause.!!!!
Wrong and dangerous advice……

I'm guessing... garbled acceleration errors on a direct reading compass? see PPRuNe

Deviations from track when in the North Atlantic Track System?

https://skybrary.aero/articles/north...ns-contingency

aha! Thank you. Severe wx avoidance without clearance deviating more than 5 NM from track. The SAND acronym got me.
​​​​​​​

Great. Why?

Because it does not work in the Southern Hemisphere nor South of the equator.
The ICAO weather deviation procedure is for all worldwide oceanic airspace not just NAT HLA.

No, it does not indeed but we are all very much aware that this -like many others- is just a mnemonic rule of thumb which could, by the way, become unusable tomorrow morning if procedures change even in the Northern Hemisphere. No need to get excited, people still look at their contingencies for different airspaces before thinking about acronyms.