A Numerical Investigation of a Slow-Moving Convective Line in a Weakly Sheared Environment

Changhai LIU

doi:10.1007/BF02918706

Impact Factor: 5.8

Volume 22 Issue 5

Sep. 2005

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Article > ADVANCES IN ATMOSPHERIC SCIENCES > 2005 > 22(5): 625-639

A Numerical Investigation of a Slow-Moving Convective Line in a Weakly Sheared Environment

Changhai LIU

1.
National Center for Atmospheric Research, Boulder, Colorado 80307-3000, USA

Changhai LIU

doi: 10.1007/BF02918706

Abstract
References
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Abstract:
A series of three-dimensional, cloud-resolving numerical simulations are performed to examine a slowpropagating, quasi-two-dimensional convective system in a weakly sheared environment during the Tropical Rainfall Measuring Mission Large-Scale Biosphere-Atmosphere (TRMM-LBA) field campaign. The focus is on the kinematics and thermodynamics, organization mechanisms, and dynamical effects of low-level shear, ice microphysics and tropospheric humidity. The control simulation, which is initialized with the observed sounding and includes full microphysics, successfully replicates many observed features of the convective system, such as the linear structure, spatial orientation, life cycle, and sluggish translation.The system at the mature stage displays a line-normal structure similar to that associated with squalltype convective systems, but the corresponding mesoscale circulation and thermodynamic modification are much weaker. Ice-phase microphysical processes are not necessary to the formation of the convective system, but they play a non-trivial role in the late evolution stage. In contrast, the low-level shear, albeit shallow and weak, is critical to the realistic realization of the convective line. The tropospheric moisture above the planetary boundary layer has an important impact on the behavior of convective organization.In particular, a dry layer in the lower troposphere significantly suppresses convective development and inhibits the generation of organized convection even though the convective available potential energy is substantial. The free-atmosphere humidity has received little attention in previous studies of organized convection and warrants further investigation.
- mesoscale convective system,
- cloud-resolving simulation
References

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Manuscript History

Manuscript received: 10 September 2005

Manuscript revised: 10 September 2005

通讯作者: 陈斌, bchen63@163.com

1.
沈阳化工大学材料科学与工程学院沈阳 110142

A Numerical Investigation of a Slow-Moving Convective Line in a Weakly Sheared Environment

Changhai LIU

1. National Center for Atmospheric Research, Boulder, Colorado 80307-3000, USA

Manuscript received: 2005-09-10
Manuscript revised: 2005-09-10

Abstract: A series of three-dimensional, cloud-resolving numerical simulations are performed to examine a slowpropagating, quasi-two-dimensional convective system in a weakly sheared environment during the Tropical Rainfall Measuring Mission Large-Scale Biosphere-Atmosphere (TRMM-LBA) field campaign. The focus is on the kinematics and thermodynamics, organization mechanisms, and dynamical effects of low-level shear, ice microphysics and tropospheric humidity. The control simulation, which is initialized with the observed sounding and includes full microphysics, successfully replicates many observed features of the convective system, such as the linear structure, spatial orientation, life cycle, and sluggish translation.The system at the mature stage displays a line-normal structure similar to that associated with squalltype convective systems, but the corresponding mesoscale circulation and thermodynamic modification are much weaker. Ice-phase microphysical processes are not necessary to the formation of the convective system, but they play a non-trivial role in the late evolution stage. In contrast, the low-level shear, albeit shallow and weak, is critical to the realistic realization of the convective line. The tropospheric moisture above the planetary boundary layer has an important impact on the behavior of convective organization.In particular, a dry layer in the lower troposphere significantly suppresses convective development and inhibits the generation of organized convection even though the convective available potential energy is substantial. The free-atmosphere humidity has received little attention in previous studies of organized convection and warrants further investigation.

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