[Lewton]

Most of these can be explained by the fact that submitting the same article as someone else counts as upvoting the first submission.

It makes sense to me that submissions comes in waves (as several HN'ers could find articles they find HN worthy through other channels at the same time)

I am sure that some manipulation happens (I imagine a lot of people use their network to ask for upvotes to their submissions if it's something important to them), it's just not that clear cut

[mintplant]

I also wonder if caching has some sort of influence. Maybe the spikes in the data are when the score is updated after a while of remaining static. The variation in this could have something to do with load levels on the site.