日間對流邊界層中的非局地動量混合

doi:10.12306/2021jms.0033

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日間對流邊界層中的非局地動量混合
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                        10.12306/2021jms.0033
                    
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中圖分類號:O357.4
基金項(xiàng)目:國家重點(diǎn)研發(fā)計(jì)劃課題（2018YFC1506802）；國家自然科學(xué)基金資助項(xiàng)目（41875011）

Non-local mixing of momentum in the daytime convective boundary layer

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摘要:

日間對流邊界層最顯著的結(jié)構(gòu)特征是在熱力作用下所形成的組織化對流。與小尺度湍渦不同的是，組織化對流具有邊界層尺度的垂直相干性，可實(shí)現(xiàn)垂直貫穿邊界層的非局地物質(zhì)和能量傳輸。本文針對對流邊界層中的動量混合，探究組織化對流對動量輸送的貢獻(xiàn)。以高精度大渦模擬數(shù)據(jù)為研究資料，通過傅里葉變換、本征正交分解和經(jīng)驗(yàn)?zāi)B(tài)分解3種濾波方法，分離組織化對流和背景湍渦，計(jì)算與兩者相關(guān)的非局地和局地動量通量，發(fā)現(xiàn)與組織化對流相關(guān)的非局地動量通量是總通量的重要組成部分，并主導(dǎo)混合層中的垂直動量輸送。而后，基于協(xié)譜和相位譜分析，探究組織化對流的空間結(jié)構(gòu)對動量傳輸?shù)挠绊懀l(fā)現(xiàn)在熱力主導(dǎo)的不穩(wěn)定環(huán)境中，單體型環(huán)流結(jié)構(gòu)對動量的傳輸效率較低。而在風(fēng)切較強(qiáng)的近中性環(huán)境中，滾渦型組織化結(jié)構(gòu)可使垂直和水平流向擾動速度的相位差減小，從而提升動量傳輸效率。研究結(jié)果表明，邊界層方案需要包含非局地動量通量項(xiàng)，其參數(shù)化應(yīng)考慮整體穩(wěn)定度對傳輸效率的影響。

Abstract:

Thermally-driven organized convection is the most prominent structural feature of the daytime convective boundary layer (CBL). Different from inertial-subrange turbulent eddies, organized convection is vertically coherent at the boundary layer scale, and can contributes to nonlocal vertical transport of mass and energy within the CBL. In this study, we investigate turbulent mixing of momentum in the CBL, with a focus on the role of organized convection in momentum transport. Based on modeled CBL with high resolution large-eddy simulations, organized convection and background turbulence are separated by using Fourier transform, Proper Orthogonal Decomposition and Empirical Mode Decomposition. The nonlocal and local fluxes associated with organized convection and background turbulence are calculated. It is found that nonlocal flux constitutes a significant portion of the total momentum flux, and dominates the transport of momentum in the mixed layer. The mechanism behind organized convective structures affect the transport of momentum is investigated based on momentum co-spectrum and phase-spectrum. Analyses reveal that convective cells generated under strong buoyancy forcing are inefficient at transporting momentum. In the near neutral environment with strong wind shear, convection organizes into horizontal roll vortices, which reduce the phase difference between vertical and horizontal streamwise perturbation velocities, thus improving the efficiency of momentum transport. This study suggests that planetary boundary layer schemes must include nonlocal momentum flux, whose parameterization should consider the influence of bulk CBL stability on momentum transport efficiency.

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趙昭,周博聞.日間對流邊界層中的非局地動量混合.氣象科學(xué),2021,41(5):631-643 ZHAO Zhao, ZHOU Bowen. Non-local mixing of momentum in the daytime convective boundary layer. Journal of the Meteorological Sciences,2021,41(5):631-643

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收稿日期:2021-01-18
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在線發(fā)布日期: 2021-11-24
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