By Jeremy Gaunt

LONDON (Reuters) - So strong is the belief in the growth momentum of the global economy as it enters the second half of 2017, the point has been reached in the economic cycle where data not meeting expectations is dismissed as an aberration.

Flash purchasing managers' indexes for services in Europe in June, for example, were weaker than anyone in a Reuters poll had predicted, but the market paid scant attention. "Way below expectations, but let's not worry," was the mantra.

Such economic Panglossianism - all for the best in the best of all worlds - is based on what seems to be a majority view among policymakers and economists that the world is enjoying a broad expansion.

"Faster growth this year reflects a synchronized improvement across both advanced and emerging market economies," Brian Coulton, Fitch Ratings' chief economist, wrote in an outlook projecting 2017 would have the fastest world growth - 2.9 percent - since 2010.

Backing up this view, central banks in the United States, euro zone and Britain are leaning toward tightening, albeit with a cacophony of mixed signals about when.

Financial markets are now pricing in a 90 percent chance of a euro zone rate hike by July next year, for example, to go with the Federal Reserve's ongoing upward tweaks.

There are, however, some inconvenient trends out there that will need consideration in the second half.

First, there have been some signs of a dip in economic activity, while inflation remains, in most places, stubbornly nonchalant toward the huge monetary stimulus thrown at it.

The Citi Economic Surprise Index, which moves in tandem with data beating or underclubbing expectations, has plunged for the main industrial nations this year and is at negative levels not seen since 2011.

Real U.S. gross domestic product has been increasing, but the pace has been slower in each of the past two quarters up to the fairly slow annualized 1.4 percent in January-March.

A report by the Atlanta Fed suggests second quarter growth will bounce back - but as a result of stronger home sales, a reflection of cheap money, offsetting sluggish equipment and inventory investment.

Durable goods orders declined sharply and jobs growth slowed at their last readings.

In the euro zone, the overall picture is relatively positive with a current 1.9 percent year-on-year growth rate - but there are centers of trouble, such as in Italy, the bloc's third largest economy. And while deflation may have gone, inflation is still below target.

The jobless rate is lower, but still above 9 percent (twice that for the young), consumer spending has been easing and wage growth is stubbornly slow.