U.S. stock buy-backs, which "goose" the stock price (up) commonly accelerate in November and December, to increase the executives' year-end bonuses (which are tied to the price of the stock):

Goldman Sachs’ David Kostin believes a temporary pullback may explain why the S&P 500 has tumbled from its all-time high of 2,019 on Sept. 19.

“Most companies are precluded from engaging in open-market stock repurchases during the five weeks before releasing earnings,” Kostin notes. “For many firms, the beginning of the blackout period coincided with the S&P 500 peak on September 18. So the sell-off occurred during a time when the single largest source of equity demand was absent. Buybacks dip during earnings reporting months, which have seen 1.2 points higher realized volatility than in other months during the past 25 years.”…

“We expect companies will actively repurchase shares in November and December,” he writes. “Since 2007, an average of 25% of annual buybacks has occurred during the last two months of the year.”

http://www.nakedcapitalism.com/2014/10/goldman-makes-it-official-that-the-stock-market-is-manipulated-buybacks-drive-valuations.html

This Goldman Sachs analyst comes right up and says that rising stock prices are dependent on these buy-backs -- the company boosting the price of its own shares by buying them.

Your chart, limited in time-span though though it is, shows dips in the third quarter and rises in the fourth. Which is consistent with the explanation I quoted, the Goldman Sachs claim that 25% of buy-back purchases have been in the last two months of the year, for the last 7+ years.

It may be self-evident that buying the shares back rises prices, but there's evidently some difference of opinion about why, as your post demonstrates.....

It's hard to see the CEOs who make these decisions as "hired managers". The whole executive pay question -- e.g., poor performance CEOs getting big raises from board members they themselves appointed -- indicates that a lot of this is just self-dealing, at the expense of the shareholders and the company itself.