Summer is often a volatile time for the market, as vacationing professionals and ordinary investors alike produce lower trading volume that can amplify reactions to news. This morning, reports that retail sales dropped 0.5% stunned analysts who were expecting a modest gain. But the real news behind the drop may come from the just-started earnings season, during which a rash of warnings has made investors anxious about the current economic environment. At around 10:45 a.m. EDT, the Dow Jones Industrials (INDEX: ^DJI) were down about 40 points.

The Dow will contribute to earnings fever this week, with a bunch of its component companies reporting. Coca-Cola (NYSE: KO) is down about 0.4%, as it gets ready to announce its second-quarter results before the market opens tomorrow morning. Analysts see the company earning $0.02 per share more than it did in the year-ago quarter, but given its high valuation, Coke may need to provide another earnings beat in order to make shareholders happy.

Johnson & Johnson (NYSE: JNJ), down just a few cents this morning, also reports tomorrow before the market opens. It, too, is expected to provide slow growth for shareholders, with earnings rising by a single penny per share over last year's figures. Despite the big interest in dividend stocks that has pushed prices higher lately, J&J has the benefit of being defensively oriented, potentially protecting investors if a bigger slowdown rears its ugly head.

Finally, JPMorgan Chase (NYSE: JPM) fell almost 2%, the big loser in the Dow. Despite positive earnings from Citigroup (NYSE: C), the banking industry is reeling from continuing revelations about the LIBOR scandal and uncertainty about future regulation. Until the banks can get their act together and get out of the negative spotlight, investors can expect to see plenty of volatility.

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