ABSTRACT
Standard weather observations include instrumental measurements of air temperature, dewpoint temperature, station pressure (adjusted to mean sea level), wind speed and direction, pressure change over the last three hours, and pressure tendency; also, visual observations are made of cloud amount, type, and cloud base height (for low, middle, and high cloud layers), visibility, and present and past weather. In addition, precipitation amounts are recorded six-hourly and snow depth once a day. Each element is reported in the international synoptic code (Stubbs, 1981; World Meteorological Organization, 1995). Observations are made at synoptic weather stations at 00.00, 00.06, 12.00 and 18.00 hours UTC (Universal Coordinated Time based on Greenwich 0° meridian) and collected at international centers. Under the World Weather Watch program, synoptic reports are made worldwide at about 4,000 land stations and by 7,000 ships (Figure 2.1). Ships also report “sea surface” temperature (nowadays usually engine room intake temperature), sea state, and, if present, sea ice conditions.
