Some plots that may be interesting, or not.
The following plots show the trade volume and the price variation for Bitstamp (BSTP) as a function of the hour of day (UTC). The plots on the left show these quantities averaged over the last nine complete months, Jan--Sep 2014. The plots on the right show the averages computed separately for the first 4 months Jan-Apr (red) and the next 5 months May--Sep (blue). (Click on images for larger versions.)
The first set, below, shows the average USD trade volume around each hour. For example, the dot on the hour marked "6" is the USD volume V traded per hour from 05:00 to 07:00 UTC, averaged over all days of the period in question (273 days on the left, 120 and 153 days on the right) with no weighting:
The second set, below, shows the average change in price at each hour. For example, the dot on the hour marked "6" shows the result of taking the logs Y0 and Y1 of the weighted mean prices P0 from 05:00 to 06:00 UTC and P1 from 06:00 to 07:00 UTC, computing the difference D = Y1 - Y0, averaging D weighted by V over the days in question, and taking the anti-log. The ordinate "0.993" for that dot means that, on average over that period, the price dropped 0.7% between 05:00 and 07:00 UTC. Note that, on these plots, a large price increase in one day will tend to cancel a large price drop at the same hour on some other day.
The third set, below, shows the root-mean-square change in price at each hour. For example, the dot on the hour marked "6" shows the result of taking the logs Y0 and Y1 of the weighted mean prices P0 from 05:00 to 06:00 UTC and P1 from 06:00 to 07:00 UTC, computing the difference D = Y1 - Y0, averaging the square D
2 weighted by V over the days in question, and taking the square root and then the anti-log. The ordinate "1.029" for that dot means that, on average over that period, the price changed by 2.9%, up or down, between 05:00 and 07:00 UTC. Note that, on these plots, changes in opposite directions (at the same hour on different days) are added, rather than cancelling out.
I hope the plots are correct. In any case here are the essentials:
Raw data (Bitstamp's volume and price data, 1 hour intervals, 2014-01-01 to 2014-09-30)
Averaging script (gawk)