B
An anti-clockwise shift in the wind direction.
Instrument that measures air pressure.
An aneroid barometer doesn't contain liquid.
Area of country, generally a larger catchment area, drained by a river and its tributaries.
Measurement of water depth in oceans, seas or lakes.
The mathematical representation of the spring–neap cycle is in terms of the two signals (in this example the semi-diurnal tides M2 and S2) going in and out of phase over the course of a fortnight.
This phenomenon is known as beats or beating and in the context of tides is not confined to M2 and S2. When any pair of slightly different frequencies (of similar amplitude) add together, their sum undergoes a regular cycle between near-zero magnitude (neaps), and a magnitude equal to the sum of the pair (springs).
The period between successive neaps is equal to the inverse of the absolute value of the difference between the two frequencies. The frequencies of M2 and S2 are 1.9322 cpd and 2.0 cpd respectively. Their difference is the beat frequency 0.0678 cpd, the inverse of which, 14.75 days, is the beat period – also known as the fortnightly or spring–neap cycle.
Scale that estimates wind speed based on the effects we feel, see and hear (human observations).
A fixed physical object or mark used as a reference for a vertical point. A tidal benchmark is a point near a tidal station used as a reference for a tide gauge and tide measurements.
Very strong and cold wind loaded with snow, some lifted off the ground.
Dust that is raised locally by the wind to a height of at least two metres above the ground. In aviation forecasts and reports it is coded as BLDU.
Snow that is raised locally by the wind to a height of at least two metres above the ground. In aviation forecasts and reports it is coded as BLSN.
The temperature at which the vapour pressure of a liquid is equal to that of the surrounding atmosphere. The boiling point of pure water at the standard sea-level pressure of 1013.25 hPa is 100°C (373°K).
A solitary tidal wave with a steep leading edge that travels up a river, estuary or bay against the direction of the river current. Also known as Tidal bore.
Used to describe an amount of cloud covering the sky of between five and seven oktas (eighths). In aviation forecasts and reports it is coded as BKN.
Upward force which lifts a parcel of air. This happens when the air parcel is less dense than the surrounding environment.
Describes the relationship of the wind direction to the pressure distribution. In the southern hemisphere, if one stands with one’s back to the wind, lower pressure is to the right. Lower pressure will be to the left in the northern hemisphere.