the sightings of july 26–27 also made front-page headlines, and led president harry truman to have his air force aide call ruppelt and ask for an explanation of the sightings and unknown radar returns. truman listened to the conversation between the two men on a separate phone, but did not ask questions himself. ruppelt, remembering the conversation he had with captain james, told the president's assistant that the sightings might have been caused by a temperature inversion, in which a layer of warm, moist air covers a layer of cool, dry air closer to the ground. this condition can cause radar signals to bend and give false returns. however, ruppelt had not yet interviewed any of the witnesses or conducted a formal investigation.