President Donald Trump speaks as he receives a status report on Hurricane Dorian in the Oval Office of the White House in Washington, September 4, 2019.

Donald Trump is tweeting more and it's affecting the bond market.

In fact, the president's market-moving tweets ballooned in August as he hammered China on trade and went after the Federal Reserve on interest rates.

In an attempt to quantify the impact of Trump's tweets on the bond market, J.P. Morgan devised a "Volfefe Index" to analyze how the president's tweets are influencing volatility in U.S. interest rates.

J.P. Morgan found that the index, named after Trump's infamous and still mysterious "covfefe" tweet, explains a measurable fraction of the moves in implied rate volatility for 2-year and 5-year Treasurys.

"This makes rough sense as much of the president's tweets have been focused on the Federal Reserve, and as trade tensions are broadly seen as, first and foremost, impactful on near-term economic performance and, likewise, the Fed's reaction to such developments," wrote the authors of the J.P. Morgan report.

Trump's market-moving messages most often address trade and monetary policy, with key words including "China," "billion" and "products." These tweets are increasingly less likely to receive favorable responses, such as likes or retweets, from the president's followers.