南京大学学报(自然科学版) ›› 2024, Vol. 60 ›› Issue (2): 276–286.doi: 10.13232/j.cnki.jnju.2024.02.009

• • 上一篇    

数值天气预报模式的行星边界层方案热力预报变量选择

赵怡雪, 周博闻()   

  1. 中尺度灾害性天气教育部重点实验室，南京大学大气科学学院，南京，210023
  • 收稿日期:2024-02-01 出版日期:2024-03-30 发布日期:2024-03-29
  • 通讯作者: 周博闻 E-mail:zhoubowen@nju.edu.cn
  • 基金资助:
    国家自然科学基金(42192555)

On the choice of prognostic thermal variable in planetary boundary layer schemes for numerical weather prediction models

Yixue Zhao, Bowen Zhou()   

  1. Key Laboratory for Mesoscale Severe Weather，Ministry of Education，and School of Atmospheric Sciences，Nanjing University，Nanjing，210023，China
  • Received:2024-02-01 Online:2024-03-30 Published:2024-03-29
  • Contact: Bowen Zhou E-mail:zhoubowen@nju.edu.cn

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摘要：

在数值天气预报模式中，大气边界层湍流混合由行星边界层方案承担.传统的边界层方案多采用位温作为热力学预报变量，计算感热通量并获得位温的湍流倾向，多数边界层方案设计之初，也往往只考虑干边界层中的位温湍流混合.事实上，驱动边界层热对流的是浮力而非热力，前者还包含了水汽的作用，由虚位温表征.基于湍流可分辨的大涡模拟来评估传统边界层方案所参数化的感热通量在湿边界层中的适用性，重点关注方案中涉及逆梯度修正项的关键系数，同时也考察浮力通量的参数化评估结果显示浮力通量在干湿边界层中具备一致性，其模式系数不随水汽条件变化，因此，推荐以虚位温替代位温作为行星边界层方案热力预报变量.

关键词: 行星边界层方案, 对流边界层, 虚位温, 浮力通量, 感热通量

Abstract:

In numerical weather prediction models，atmospheric boundary layer turbulence is parameterized via planetary boundary layer (PBL) schemes. Traditional PBL schemes often adopt potential temperature θ as the prognostic thermal variable，compute sensible heat flux and the corresponding θ?tendency. As such，most PBL schemes are designed by considering turbulent mixing of θ in a dry boundary layer. In fact，boundary layer convection is driven by buoyancy rather than sensible heat. The former accounts for moisture effects，and is represented by the virtual potential temperature θv. Based on turbulence?resolving large?eddy simulations，this study evaluates the applicability of sensible heat flux?based turbulence parameterizations in the moist boundary layer，focusing on counter?gradient correction related model coefficients. The performance of buoyancy flux?based parameterization is also investigated. It is found that buoyancy fluxes are consistent for the dry and moist boundary layers，with identical model coefficients for both cases. This study therefore recommends the use of θv instead of θ as the prognostic thermal variable for PBL schemes.

Key words: planetary boundary layer scheme, convective boundary layer, virtual potential temperature, buoyancy flux, sensible heat flux

中图分类号: 

  • P445

图1

左图为对流边界层典型热力结构示意图，实线代表边界层热泡，右图为虚位温Θv和垂直湍流浮力通量w'θv'ˉ的垂直廓线示意图（zi和BS 分别代表边界层高度和地表浮力通量，改自赵昭和周博闻[11]）"

图2

海洋浅积云边界层中的垂直浮力通量及其组成分量的垂直廓线（数据源自对Barbados Oceanographic and Meteorological Experiment (BOMEX)个例的大涡模拟[13]）"

图3

六个具有不同波文比的理想对流边界层中的(a)感热通量w'θ'ˉ和(b)浮力通量w'θv'ˉ垂直廓线"

表1

BOMEX个例和干对流边界层个例的关键实验参数设置"

个例w'θs'¯K⋅m⋅s-1w'rvs'¯m⋅s-1w'θvs'¯K⋅m⋅s-1u*m⋅s-1Ugm⋅s-1zim-LOmzi/ LO-
BOMEX8.0×10-35.2×10-51.8×10-20.28-10+1.8×10-3z545935.9
CBL5.0×10-205.0×10-20.501010071835.5

图4

BOMEX个例的(a)垂直感热通量和(b)垂直浮力通量收支（图注参照式(9)与式(17)）"

图5

如图4，CBL个例的垂直感热通量收支"

图6

(a) BOMEX个例和(b) CBL个例中的无量纲b系数（参见式(10)）蓝线和绿线针对感热通量w'θ'ˉ分别采用了w*d和w*m定义，红线代表的是浮力通量w'θv'ˉ，采用w*m定义."

图7

(a) BOMEX个例中的感热通量(黑线)和浮力通量(红线)收支中的气压项和(b) CBL个例中的感热即浮力通量收支中的气压项"

图8

BOMEX个例中的标准化逆梯度修正项（式（16））及不同的b系数"

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