The lunar diurnal variation of atmospheric temperature at Batavia, 1866-1928

Abstract

The existence of a lunar tide in the earth’s atmosphere is now a well-established fact. It is indicated by a lunar semidiurnal variation of barometric pressure, found at every station for which the necessary reductions have been made. Now a variation of pressure in a gas is in general accompanied by a variation of temperature. The amount of this variation depends on the rate at which heat can flow in the gas, from a region of compression to one of rarefaction, or from the earth or ocean to or from the gas. The maximum variation of temperature corresponds to adiabatic changes of pressure, while if the heat flow can be very rapid, the temperature variation may be reduced almost to zero, corresponding to isothermal changes of pressure. I have shown that the lunar tidal changes of pressure will be almost adiabatic so far as concerns heat flow in the gas , between regions of compression and of rarefaction. The long time available for equalisation of temperature, viz., a quarter of a lunar day, or about 6 hours, is in fact ineffective because of the long wave-length of the tide, the distance between the regions of highest or lowest pressure in any latitude being a quarter of the circumference of the circle of latitude. The temperature variation might be reduced below the adiabatic value if vertical flow of heat, between the air and the ground or ocean, is sufficiently rapid. This point will be discussed in another paper; the conclusion reached is that the vertical flow of heat is unlikely to be important over the land . Hence a temperature variation approaching the adiabatic value is likely to be associated with the lunar atmospheric tide at a land station.