The tide is a periodic rise and fall in the level of the ocean and other large water bodies. Tides occur when the moon and to some extent the sun exert a gravitational pull on the water bodies on the earth.
A lunar day is time taken by the earth to complete one rotation with respect to the moon (24 hrs 52 min)
Lunar month is time taken by the moon to complete one revolution around the earth (27.3 days)
The moon is always ahead of the earth by 52 minutes due to its revolution e.g. if Nairobi is opposite the moon at 6 pm the following day the high tide will be at 6.52 pm.
The tidal range is the difference between the highest level reached by high tide and the lowest level reached by low tide.
Types of tides
- Spring Tides In which the highest and lowest tides occur.
Occurs when the sun, moon, and the earth are in a line (syzygy position) and pulling in the same plane causing pulling force to be greatest.
- Neap Tides
In which high tide is lower than normal and low tide is higher than normal.Occurs when the sun, moon and earth form a right angle and pulling water to themselves.
- Perigian Tides
In which the tidal range is 20% higher than normal. Occur when the moon is nearest to the earth (perigee position) causing pulling force to be greatest.
- Apogean Tides
In which tidal range is lower than normal. Occur when moon is farthest from the earth (apogee position) causing pulling force to be weakest.
- Diurnal Tides
1H1L in a lunar day
f) Semi Diurnal Tides
2H2L in a lunar day which may rise or drop at the same level.
Occur in most of Pacific Ocean.
- Mixed Tides
2H2L in a lunar day when one pair may fluctuate in level while the other remains constant.