A Note on Certain Interesting Ageostrophic Motions in a Rotating Hemispherical Shell

Certain aspects of Long's experiments (and some later extensions) with fluid motions around obstacles in a rotating hemispherical shell are discussed. For westerly currents, Long demonstrated that Rossby-Haurwitz waves could be produced at proper values of an angular kinematic Rossby number, R ≡ ωr/Ω. These and a wide variety of other experiments give strong evidence of quasi-geostrophic properties when-ever suitable kinematic Rossby numbers are of the order of 0.1. On the other hand, easterly currents of about the same intensity as give Rossby-Haurwitz waves for westerly currents, give with a long meridional barrier a cusped wave pattern of a much more ageostrophic character than Rossby-Haurwitz waves. Some general questions suggested by this phenomenon, especially concerning the possibility of a genera1 stability difference between east- and west-wind currents, are posed.