The U.S. bull market keeps on ticking.

Shares in the Standard & Poor’s 500 Index have rallied back to an all-time high, recouping losses in a 10-day advance that brought the index within 0.5 percent of 2,000. The rebound was the sixth in two years where equities needed less than two weeks to recover after a drop of 2 percent or more, according to data compiled by Sundial Capital Research Inc.

The V-shaped pattern of losses followed by gains is recurring more often than any time in almost eight decades, Sundial data show. Investors are quick to both sell and buy in a market that has gone almost three years without a retreat of 10 percent as the strengthening U.S. economy puts a floor under declines spurred by crises from Argentina to Ukraine.

“It’s like trying to push a beach ball underwater and having it pop right back up,” John Manley, who helps oversee about $233 billion as chief equity strategist for Wells Fargo Funds Management in New York, said. “That’s what’s been happening to equity markets as the Federal Reserve has been accommodative.”

Almost $900 billion has been restored to American equity values since early August and the S&P 500 is heading for a third straight weekly advance, bolstered by easing tensions in Ukraine and speculation that the Fed will continue to support the economic expansion.

Record High

Stocks rallied as data showed fewer Americans than forecast applied for unemployment benefits last week and purchases of previously owned U.S. homes unexpectedly rose in July.

The gains are coming after the S&P 500 started August with the worst weekly decline in more than two years. The index tumbled 2.7 percent over the five days through Aug. 1 as Argentina defaulted on debt, President Barack Obama announced new sanctions against Russia and U.S. gross domestic product expanding at 4 percent spurred concern that the Federal Reserve may lift interest rates sooner than anticipated.

The index reached a two-month low on Aug. 7 and has since risen in all but two days.

“There is a great hesitation to buy at new highs and then feel stupid when the inevitable correction hits,” Jason Goepfert, president of Sundial in Blaine, Minnesota, wrote in an e-mail. “So once we’ve seen a bit of a dip, we can rationalize to ourselves that, ‘Well, at least I didn’t buy at the high, even if we do decline further.’ That feeds on itself and pretty soon we’re right back at new highs again.”

V-Shaped Move

Goepfert found that the only time when V-shaped rebounds happened more often than now was during the two years through December 1936. At that time, seven occurred.

He defines the move as a drop of at least 2 percent over five to 10 days and a subsequent gain of a similar magnitude over a comparable period. During the process, prices have to set at least a one-month low and not fall back within 0.5 percent of the bottom on a closing basis.

The U.S. stock market has experienced similar patterns in the first two months of 2014. The S&P 500 sank 2.1 percent on Jan. 24 and 2.3 percent on Feb. 3 before bottoming. Over the next six days, the index pared most of the losses, jumping 4.5 percent.

“Some of the downturns had to do with geopolitical concerns, and in some cases those have abated a bit and the market has bounced back,” John Carey, a Boston-based fund manager at Pioneer Investment Management Inc., which oversees about $220 billion, said. “The outlook for the rest of the year is pretty positive.”