1. The Movement of Rossby WavesLike all atmospheric phenomena, the
movement of Rossby waves results not from mere chance, but from the
combined actions of numerous physical forces. Three factors determine
the rate at which a Rossby wave propagates: (1) the westerly component
of its internal wind speed, (2) its latitudinal position, and (3) its
wavelength. In particular, Rossby waves with vigorous winds and shorter
wavelengths move most rapidly, as indicated by the formula...where C is
the speed at which the wave propagates downwind (m/sec), U is the
average westerly component of the wind speed within the wave (m/sec), b
is a function of latitude equal to 1.6 × 10−11 m−1 sec−1 at 45°, and L
is the wavelength (m).The rates of downwind migration for Rossby waves
at 45° latitude with various wavelengths and wind speeds are presented
in Table 8-2-1. As you can see, a wave having a westerly wind speed of
20 m/sec (45 mph) and a wavelength of 3000 km advances 60 percent faster
than does one with the same speed but a wavelength of 5000 km (16 m/sec
vs. 10 m/sec).For a given wind speed and latitude, there is some
particular wavelength, Lcrit, at which the waves do not migrate at all.
Waves longer than this critical value actually migrate from east to west
and are said to be retrograding waves. By rearranging the equation and
setting C = 0 (that is, by assuming the waves are stationary), we can
determine the critical wavelength:...For example, at 45° a Rossby wave
with a jet stream speed of 40 m/sec will migrate upwind if its
wavelength is more than about 10,000 km. This, however, is a
particularly long wavelength. At high wind speeds, retrograding motion
occurs only for exceptionally long waves, which are quite rare. For
lower wind speeds, the critical wavelength is less (only 5000 km for
wind at 10 m/sec): As it happens, shorter waves (with lower wind speeds)
are more common. Thus, when westward movement appears, it tends to
occur when upper-level winds are weak, not strong.TABLE 8-2-1...How is a
Rossby wave’s wavelength related to wave speed? Get solution
2. The Movement of Rossby WavesLike all atmospheric phenomena, the movement of Rossby waves results not from mere chance, but from the combined actions of numerous physical forces. Three factors determine the rate at which a Rossby wave propagates: (1) the westerly component of its internal wind speed, (2) its latitudinal position, and (3) its wavelength. In particular, Rossby waves with vigorous winds and shorter wavelengths move most rapidly, as indicated by the formula...where C is the speed at which the wave propagates downwind (m/sec), U is the average westerly component of the wind speed within the wave (m/sec), b is a function of latitude equal to 1.6 × 10−11 m−1 sec−1 at 45°, and L is the wavelength (m).The rates of downwind migration for Rossby waves at 45° latitude with various wavelengths and wind speeds are presented in Table 8-2-1. As you can see, a wave having a westerly wind speed of 20 m/sec (45 mph) and a wavelength of 3000 km advances 60 percent faster than does one with the same speed but a wavelength of 5000 km (16 m/sec vs. 10 m/sec).For a given wind speed and latitude, there is some particular wavelength, Lcrit, at which the waves do not migrate at all. Waves longer than this critical value actually migrate from east to west and are said to be retrograding waves. By rearranging the equation and setting C = 0 (that is, by assuming the waves are stationary), we can determine the critical wavelength:...For example, at 45° a Rossby wave with a jet stream speed of 40 m/sec will migrate upwind if its wavelength is more than about 10,000 km. This, however, is a particularly long wavelength. At high wind speeds, retrograding motion occurs only for exceptionally long waves, which are quite rare. For lower wind speeds, the critical wavelength is less (only 5000 km for wind at 10 m/sec): As it happens, shorter waves (with lower wind speeds) are more common. Thus, when westward movement appears, it tends to occur when upper-level winds are weak, not strong.TABLE 8-2-1...What is a retrograding wave and under what conditions do they commonly occur? Get solution
2. The Movement of Rossby WavesLike all atmospheric phenomena, the movement of Rossby waves results not from mere chance, but from the combined actions of numerous physical forces. Three factors determine the rate at which a Rossby wave propagates: (1) the westerly component of its internal wind speed, (2) its latitudinal position, and (3) its wavelength. In particular, Rossby waves with vigorous winds and shorter wavelengths move most rapidly, as indicated by the formula...where C is the speed at which the wave propagates downwind (m/sec), U is the average westerly component of the wind speed within the wave (m/sec), b is a function of latitude equal to 1.6 × 10−11 m−1 sec−1 at 45°, and L is the wavelength (m).The rates of downwind migration for Rossby waves at 45° latitude with various wavelengths and wind speeds are presented in Table 8-2-1. As you can see, a wave having a westerly wind speed of 20 m/sec (45 mph) and a wavelength of 3000 km advances 60 percent faster than does one with the same speed but a wavelength of 5000 km (16 m/sec vs. 10 m/sec).For a given wind speed and latitude, there is some particular wavelength, Lcrit, at which the waves do not migrate at all. Waves longer than this critical value actually migrate from east to west and are said to be retrograding waves. By rearranging the equation and setting C = 0 (that is, by assuming the waves are stationary), we can determine the critical wavelength:...For example, at 45° a Rossby wave with a jet stream speed of 40 m/sec will migrate upwind if its wavelength is more than about 10,000 km. This, however, is a particularly long wavelength. At high wind speeds, retrograding motion occurs only for exceptionally long waves, which are quite rare. For lower wind speeds, the critical wavelength is less (only 5000 km for wind at 10 m/sec): As it happens, shorter waves (with lower wind speeds) are more common. Thus, when westward movement appears, it tends to occur when upper-level winds are weak, not strong.TABLE 8-2-1...What is a retrograding wave and under what conditions do they commonly occur? Get solution
