I assume that is a graph of community exercise attributable to bitcoin-qt.

My speculation for the sharp peaks can be that there’s a low stage of chatter the place the node finds out whether or not friends have new information utilizing small stock messages. Often a peer has new information and the peaks may symbolize the precise bulk switch of that newly found information in bigger information messages.

The newly found information might come up from newly created unconfirmed transactions or from newly mined blocks.

I suppose the one method to really verify this is able to be to correlate the community exercise with bitcoin log entries.

I might use Wireshark or one other network-sniffer to seize and decode the information being despatched & acquired. I consider Wireshark has protocol decoders for Bitcoin site visitors.