The Lunar Tidal Model - Part 1
The Lunar Tidal Model - Part 2
The Lunar Tidal Model - Part 3
An MJO is a complex atmospheric wave that moves from west-to-east along the equator. It is most evident when it couples with atmospheric convection/precipitation between East Africa and the equatorial Western Pacific Ocean. It consists of an active region of enhanced precipitation/uplift followed by a region of suppressed precipitation. The precipitation pattern takes about 30 – 60 days to complete one cycle when seen from a given point along the equator.
The slow-moving MJO wave can be thought of as a combination of an easterly moving Kelvin-wave and a westerly moving equatorial Rossby wave. The compound MJO wave moves with a group velocity of about 5 m/sec from west-to-east. Within the large MJO wave train, Kelvin waves move from west-to-east with a phase velocity of 15 to 20 m/sec, and the equatorial Rossby Waves travel from east-to-west with a phase velocity of 5 m/sec.
Equatorial Rossby Waves (ERW)
In parts 1, 2, and 3, it was shown that the westward-moving ERWs trailing the active phase of the MJO are being generated at the times when there is an ebb in the lunar-induced atmospheric/oceanic tides at the Earth's equator [when measured at the same time in the 24.8-hour lunar tidal day], i.e. either at a tidal minimum (at a lunar standstill) or at a tidal maximum at the Earth's equator (at a lunar equatorial crossing).
Figure 2 reminds us that these ebbs in the lunar-induced atmospheric/oceanic tides at the Earth's equator occur roughly every 6-7 days, either when the peak of the Moon's tidal bulge crosses the Earth's equator (tidal maximum) or when it reaches its maximum distance from the Earth's equator i.e. lunar standstill (tidal minimum).
Equatorial Kelvin Waves (EKW)
This leads us to modify our original hypothesis so that it reads:
EKWs are generated when the peak in the lunar-induced tides passes through the local meridian at either 4:00 a.m. or 4:00 p.m. local time when the diurnal surface pressure is a minimum (this takes place roughly once every quarter of a synodic month = 7.38 days). In addition, if the generation of an EKW occurs at roughly the same time as the generation of an ERW (which takes place roughly once every quarter of a Tropical month = 6.83 days), the combined atmospheric waves reinforce the Westerly Wind Bursts (WWBs) that are produced by ERWs.
Further research is being carried out to test this modified hypothesis.