The graph shows the mean orbital inclination and the mean radius vector.
According to
NASA's Mission Status (pdf, 1.2 MiB), Aqua performs inclination adjust maneuvers (IAMs) to maintain the local mean time as measured at the ascending node between 13:30 and
13:45 (mission goal starting in 2011: 13:35:45 ± 45 seconds, see next graph).
Aqua's ascending orbit crosses the equator at 1:35 pm local time during each orbit (hence the original designation "EOS/PM-1").
According to
NASA's Facts (pdf, 152 KiB), the combination of morning observations (performed by
Terra) and afternoon observations will allow studies concerning the diurnal variability of many of the parameters related to the Earth's water cycle.
This graph shows the actual equatorial crossing
LMT and the difference between the geographic longitude of the satellite and of the Sun.
LMT is calculated as:
LMT = UTC + lon / 15, where
lon is the geographic longitude of the satellite when it crosses the equator.