Morphology of noctilucent clouds

Abstract

Noctilucent clouds have been hypothesized to be composed of dust particles which are enlarged by sublimation of water vapor. A meteoritic origin of the solid particles has been questioned on grounds of lack of the proper asymmetry in meteor dust impact. Reevaluation of this factor indicates that there is a marked latitudinal gradient which will result in significantly higher concentrations in the polar regions. Also, analysis of Meteorological Rocket Network wind data shows a poleward meridional flow centered at the stratopause which is assumed to diverge upward in the noctilucent cloud latitudes and to provide the reduced fall rate required for development of the observed high particulate concentrations. There is a possibility that moisture‐enriched low‐latitude stratospheric air is advected and condensed by this meridional and vertical flow system. The occurrence of noctilucent clouds is consistent with available data, and they are our most efficient natural probes of stratospheric and mesospheric circulations.

Scaling in global tidal dissipation of the Earth-Moon system

“…i.e., about 6.6 mW m −2 , where 1TW=10 12 Watt inferred from the time rate-of-change in the angular momentum J = mj of the Moon (Garrett & Munk 1971;Webb 1982;Dickey et al 1994). Presently, Ω/ω ≃ 30, whereby Erot is mostly dissipated into heat, powering H at merely three percent efficiency.…”

“…Consistency of h0 with dynamical tidal amplitude is somewhat coincidental in view of the relatively minor deformation of the Earth's mantle (Wahr 1995) and an appreciable Q-factor in the ocean tides (e.g. Webb 1982). By the first law of thermodynamics, the Earth's rotational energy Erot = 1 2 IΩ 2 is deposited into the Moon's orbit, H ≃ −GM m/(2a) and heat, the latter by tidal dissipation in the Earth…”

“…The damping coefficient can also be expressed in terms of the decay time τ d = 1/ǫω0. For instance, ǫ = 0.07, corresponds to a decay time of about 30 hours (Hendershott & Munk 1970;Webb 1982) with corresponding present-day Q0 ≃ 7 (cf. MacDonald 1964;Garrett & Munk 1971;Webb 1973).…”

“…However, a detailed quantitative account for the overall Moon's migration time due to various nonlinear dissipation channels (Stoker 1948(Stoker , 1957Munk 1968;Egbert & Ray 2001), remains to be identified. ⋆ E-mail: mvp@sejong.ac.kr Tidal dissipation (Garrett & Munk 1971;Webb 1982;Dickey et al 1994) has various mechanisms in shallow water wave theory, some of which have recently been highlighted in detailed numerical simulations on ocean dynamics and dissipation covering relatively short initial and present epochs (e.g Touma & Wisdom 1994Egbert & Ray 2004;Stammer et al 2014). Dissipation generally occurs when nonlinear steepening exceeds the mitigating effect of dispersion.…”

Wind measurements in the subpolar mesosphere region

“…The remaining ten high-energy Loki motors and slim dart systems were fired at Fort Greely beginning at noon on August 6, 1966, and continuing through 1400 LST on August 8, 1966 (Table 1). Eight of the ten soundings produced One explanation for the formation and maintenance of these extremely high-altitude clouds is offered by Webb [1965Webb [ , 1966a in his treatment of the stratospheric tidal jet (STJ). Lindzcn [1966] computed theoretical values for the thermally driven atmospheric tides.…”