I asked this in another thread, but would you mind shining a little light onto the crazy hashrate/difficulty excursions that I am seeing on the sumo pool several times a day recently? 

I'm not a very experienced miner, in fact sumo.fairpool is the first pool that I've mined for any amount of time (couple weeks now) - so this may be obvious to more experienced people.

It seems overall difficulty stays 'normally' around 6-8k (might be a little off) and the total Hashrate for sumo is about 25M/hs

From time to time (generally several times in a 24 hour period) the hashrate jumps to 35-43M/hs and therefore difficulty increases to 9-11k.  Usually this lasts several hours and then SUMO returns to 'normal'

Is the the result of large mining farms jumping from one coin to another ?  Doesn't PPLNS make that 'not as attractive' or is their hashrate just so large it is inconsequential to them ?

As I'm new to this my Hash is only about 2Kh/s which brings me just under 1 sumo/day however during these big difficulty jumps I drop to under /5 SUmo daily.  This brings my daily average down to .6-.7 according to how long these big guys stay around for.

I appreciate any knowledge you can give me about this.  Thank you.