A day with thunderstorms occurs if thunder is heard. Sunshine In Canada, bright sunshine observations are made using the Campbell-Stokes sunshine recorder, first developed in 1863. It consists of a 10-cm glass sphere which focuses sunlight on a card calibrated in hours. Sunlight burns a trace on the card, allowing the observer to determine to the nearest tenth of an hour the amount of sunshine that occurs on a given day. For example, sunshine immediately after sunrise and just before sunset would not be bright enough to register.
Values given in the tables are the average number of hours per month or year.
Station Pressure Station pressure is the force exerted on the earth's surface by a column of air of unit cross-sectional area extending from the surface of the earth to the outer limit of the atmosphere. The standard instrument for the measurement of atmospheric pressure is the mercury barometer, in which the air pressure is balanced against the weight of a column of mercury in a glass tube that contains a vacuum. Moisture Vapour pressure is the pressure exerted by the moisture in the air. It increases with both atmospheric temperature and moisture content. It is related to relative humidity in that the latter is the ratio of the actual value of vapour pressure to its value if the air were saturated at the same temperature.