文档介绍：CHAPTER 35
WEATHER ELEMENTS
GENERAL DESCRIPTION OF THE ATMOSPHERE
3500. Introduction The standard atmosphere is a conventional vertical
structure of the atmosphere characterized by a standard sea-
Weather is the state of the earth’s atmosphere with re- level pressure of millibars of mercury ( inch-
spect to temperature, humidity, precipitation, visibility, es) and a sea-level air temperature of 15° C (59° F). The
cloudiness, and other factors. Climate refers to the average temperature decreases with height (., standard lapse
long-term meteorological conditions of a place or region. rate) being a uniform 2° C (° F) per thousand feet to 11
All weather may be traced to the effect of the sun on the kilometers (36,089 feet) and thereafter remains constant at
earth. Most changes in weather involve large-scale horizon- –° C (° F).
tal motion of air. Air in motion is called wind. This motion Research has indicated that the jet stream is important
is produced by differences of atmospheric pressure, which in relation to the sequence of weather. The jet stream refers
are attributable both to differences of temperature and the to relatively strong (≤60 knots) quasi-horizontal winds,
nature of the motion itself. usually concentrated within a restricted layer of the atmo-
Weather is of vital importance to the mariner. The sphere. There are monly known jet streams. The
wind and state of the sea affect dead reckoning. Reduced sub-tropical jet stream (STJ) occurs in the region of 30°N
visibility limits piloting. The state of the atmosphere affects during the northern hemisphere winter, decreasing in sum-
electronic navigation and munication. If the skies mer. The core of highest winds in the STJ is found at about
are overcast, celestial observations are not available; and 12km altitude (40,000 feet) an in the region of 70°W, 40°E,
under certain conditions refraction and dip are disturbed. and 150°E, although considerable variab