饱和湿大气Brunt-V3/4is3/4l3/4频率及修正的相当位温

THE BRUNT-VAISALA FREQUENCY IN A SATURATED ATMOSPHERE AND THE REVISED EQUIVALENT POTENTIAL TEMPERATURE

中文关键词:  饱和湿空气  Brunt-V3/4is3/4l3/4频率  相当位温

英文关键词:Saturated atmosphere  Brunt-V3/4is3/4l3/4 frequency  Equivalent potential temperature

中文摘要:

      实际大气中受扰动的饱和气块发生凝结后,凝结水会部分脱离气块。以前研究饱和湿大气的Brunt-V3/4is3/4l3/4频率(N_m²)没有考虑凝结水的部分脱离,相当位温(θ_e)也忽略了饱和气块的混合比的作用。文中针对这些不足,在假设饱和空气中只存在气液转换条件下,推导出液态水部分脱离气块的、更符合实际情况的N_m²表达式和修正的饱和湿大气θ_e表达式。新的N_m²表达式增加了部分脱离气块的液态水的作用项,新的θ_e表达式中包含有饱和气块的混合比,并对有关的表达式分别作了讨论和比较。

英文摘要:

      If a parcel of air is displaced slightly upward in an unsatured atmosphere, it will cool by adiabatic expansion. If the atmosphere is saturated, upward displacements are also accompanied by condensation and latent heating. After an infinitesimal perturbation, the condensed liquid water will drop partially out of the parcel. This phenomenon was not described in the Brunt-V3/4is3/4l3/4 frequency(N_m²) in previous studies, although they have been studied in many aspects, especially in the stability reduction quantified by deriving an expression for the saturat ed Brunt-V3/4is3/4l3/4 frequency(N_m²). At the same time, deriving an expression for equivalent potential temperature(θ_e) in previous studies also omits a term, mixing ratio of saturated vapor in air parcel. For simplicity, we consider only liquid-vapor phase transitions during derivation. A new formula of expressing N_m², according to an air parcel change in a saturated at mosphere, is derived, discussed, and compared with original expression. It contains an additional term: the liquid water dropping partially out of the parcel, so that the new formula of expressing N_m² accurately describes an air parcel change in a saturated atmosphere, it is useful in theory. In Section 3, an accurate formula of expressing θ_e is derived under the condition that no neglecting the mixing ratio of saturated vapor. Results are estimated and compared with two other θ_e formulas. Results of the new equivalent potential temperature (θ_e) are showed the less error in middle and high at mosphere. These two revised formulas N_m² and θ_e describing the stability of a saturated atmosphere are reasonably accurate and applicable for the dynamic diagnosis.