Quasi-Equilibrium and Weak Temperature Gradient Balances in an Equatorial Beta-Plane Model
Quasi-Equilibrium and Weak Temperature Gradient Balances in an Equatorial Beta-Plane Model
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DOI：
10.1175/jas-d-20-0184.1
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发表时间：
2020-10
影响因子：
3.1
通讯作者：
F. Ahmed;J. Neelin;Á. Adames
中科院分区：
文献类型：
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作者：
F. Ahmed;J. Neelin;Á. Adames
对流准平衡(QE)和弱温度梯度(WTG)平衡常被用来研究热带大气。这项研究使用线性化的赤道β平面解来检查这些平衡的相关制度。波解的特征是水温比(Q-T比)和主导热力学平衡。经验约束的降水闭合赋予对流对温度(εt)和湿度(εq)不同的敏感性。长波赤道开尔文波和罗斯比波趋于QE平衡，εt：εQ的Q-T比可达~1-3。与严格QE的偏离是降水和波动动力学所必需的，随着波数的增加而增加。由于有效的总湿稳定摩夫，传播的QE模降低了相速度，当εt>；0时进一步减小。在短波区出现了符合WTG平衡和大Q-T比(>；10)的水汽模，这些水汽模同时存在开尔文波和罗斯比波的子午线结构。在υ=0的情况下，长传播的重力波是不存在的，只出现在一个截止波数之外。确定了波解中的两个分叉，并用它们确定了QE-WTG转换和重力波出现的空间尺度。这些尺度受对流和重力波调整时间的竞争所支配，并受中尺度函数的调制。近零值使QE-WTG的跃迁波数趋于零。当包括MEF<；0或水汽平流/水汽机制时，连续转变取代了分叉，但与波数有关的QE和WTG平衡在性质上保持不变。在长波/短波区域，快速衰减的对流/重力波模分别调整为缓慢演化的QE/WTG态。
Convective quasi-equilibrium (QE) and weak temperature gradient (WTG) balances are frequently employed to study the tropical atmosphere. This study uses linearized equatorial beta-plane solutions to examine the relevant regimes for these balances. Wave solutions are characterized by moisture–temperature ratio (q–T ratio) and dominant thermodynamic balances. An empirically constrained precipitation closure assigns different sensitivities of convection to temperature (εt) and moisture (εq). Longwave equatorial Kelvin and Rossby waves tend toward the QE balance with q–T ratios of εt:εq that can be ~1–3. Departures from strict QE, essential to both precipitation and wave dynamics, grow with wavenumber. The propagating QE modes have reduced phase speeds because of the effective gross moist stability meff, with a further reduction when εt > 0. Moisture modes obeying the WTG balance and with large q–T ratios (>10) emerge in the shortwave regime; these modes exist with both Kelvin and Rossby wave meridional structures. In the υ = 0 case, long propagating gravity waves are absent and only emerge beyond a cutoff wavenumber. Two bifurcations in the wave solutions are identified and used to locate the spatial scales for QE–WTG transition and gravity wave emergence. These scales are governed by the competition between the convection and gravity wave adjustment times and are modulated by meff. Near-zero values of meff shift the QE–WTG transition wavenumber toward zero. Continuous transitions replace the bifurcations when meff < 0 or moisture advection/WISHE mechanisms are included, but the wavenumber-dependent QE and WTG balances remain qualitatively unaltered. Rapidly decaying convective/gravity wave modes adjust to the slowly evolving QE/WTG state in the longwave/shortwave regimes, respectively.