Evaluation of an Explicit One-Dimensional Time Dependent Tilting Cloud Model: Sensitivity to Relative Humidity

1500 ◽  
Vol 999992 (9992) ◽  
pp. 99095-99121
Author(s):  
Shu-Hua dummyCHEN ◽  
Yang-Cheng dummySIAO
Keyword(s):  
Relative Humidity ◽  
Cloud Model ◽  
Time Dependent ◽  
Model Sensitivity ◽  
One Dimensional

An Explicit One-Dimensional Time-Dependent Tilting Cloud Model

2004 ◽  
Vol 61 (23) ◽  
pp. 2797-2816 ◽  
Author(s):  
Shu-Hua Chen ◽  
Wen-Yih Sun
Keyword(s):  
Mass Flux ◽  
Cloud Model ◽  
Deep Convection ◽  
Evaporative Cooling ◽  
Precipitation Amount ◽  
Time Dependent ◽  
Lower Atmosphere ◽  
Cumulus Parameterization ◽  
One Dimensional ◽  
Tilting Angle

Abstract An explicit one-dimensional time-dependent tilting cloud model has been developed for use in cumulus parameterizations. The tilting axis is not necessarily orthogonal to the (r, θ) plane, making the horizontal axisymmetric assumption more reasonable. This explicit time-dependent tilting model (ETTM) consists of an updraft and a downdraft, which are governed by the same dynamic and thermodynamic equations. The updraft is initiated by a moist thermal bubble, while the downdraft is consequently induced by evaporative cooling and the drag force of precipitation separating from the tilting updraft instead of being arbitrarily initialized. The updraft is capable of reproducing the major features of a deep cloud such as overshooting cooling above the cloud top, evaporative cooling near the surface, and drying in the lower atmosphere at dissipating stages. The entrainment–detrainment rate in this model is well defined, and its time variation is quite significant. Moreover, the vertical profile of the air inside the updraft does not follow the moist adiabat after deep convection. For the downdraft, the total precipitation and mass flux at low levels contributed from the downdraft cannot be neglected in this case study. In addition, the downdraft can bring dry air from middle levels to lower levels. Three sensitivity tests—the environmental sounding, the tilting angle, and the radius of the updraft–downdraft— have also been conducted. The cooling–warming of a downdraft near the surface is sensitive to the environmental sounding, consistent with results from Srivastava. The cloud life span, maximum vertical velocity, precipitation amount, and vertical mass flux are strongly influenced by the tilting angle and the radius of the cloud. The results from the ETTM simulation are quite reasonable and promising. However, some deficiencies of this model still exist, and more research will be conducted to improve its performance. The final goal is to implement this 1D model in a mesoscale model's cumulus parameterization scheme.

A One-Dimensional Cloud Model with Trimodal Convective Outflow

2009 ◽  
Vol 22 (23) ◽  
pp. 6437-6455 ◽  
Author(s):  
Ian Folkins
Keyword(s):  
Relative Humidity ◽  
Cloud Model ◽  
Lower Troposphere ◽  
Lapse Rate ◽  
Tropical Atmosphere ◽  
One Dimensional ◽  
Convective Clouds ◽  
Convective Scale ◽  
The Stability ◽  
Melting Level

Abstract The author describes a one-dimensional cloud model designed to investigate the relationships between stratiform downdrafts, congestus outflow, stability, and relative humidity in the tropical lower troposphere. In the tropics, the climatological lapse rate varies with height below the melting level in a way that is inconsistent with the assumptions of either moist pseudoadiabatic or reversible adiabatic ascent. This anomalous variation is referred to as the melting-level stability anomaly (MLSA). It is argued that the MLSA is caused by a transition from static to dynamic downdrafts at the melting level. Above the melting level, evaporation of precipitation cools and moistens the tropical atmosphere but does not generate downdraft parcels with sufficient negative buoyancy to descend between model levels. Below the melting level, the evaporative cooling associated with stratiform precipitation is strong enough to overcome the stability of the atmosphere and generate a convective-scale circulation. The vertical descent within these downdrafts induces a compensatory ascent in the background atmosphere that changes the overall cooling-to-moistening downdraft ratio. The inclusion of this stratiform downdraft circulation brings the modeled lapse rate and relative humidity profiles into simultaneous agreement with observations. The transition from static to dynamic downdrafts is triggered, in the model, by imposed increases in the amount of rain falling outside clouds, in the out-of-cloud rain rate, and in the vertical coherence of the rain shafts. The destabilization of the lower tropical atmosphere triggered by the stratiform circulation affects the development of convective clouds. In particular, the melting-level stability anomaly increases detrainment near the melting level and gives rise to the congestus mode.

scholarly journals A One-dimensional Time Dependent Cloud Model

2002 ◽  
Vol 80 (1) ◽  
pp. 99-118 ◽  
Author(s):  
Shu-Hua CHEN ◽  
Wen-Yih SUN
Keyword(s):  
Cloud Model ◽  
Time Dependent ◽  
One Dimensional

scholarly journals Hamiltonian Approach to Magnetic Fields with Toroidal Surfaces

1985 ◽  
Vol 40 (10) ◽  
pp. 959-967
Author(s):  
A. Salat
Keyword(s):  
Magnetic Field ◽  
Hamiltonian System ◽  
Magnetic Fields ◽  
Constant Pressure ◽  
Time Dependent ◽  
Hamiltonian Approach ◽  
One Dimensional ◽  
Mhd Equilibrium ◽  
Magnetic Surfaces ◽  
Rotational Transform

The equivalence of magnetic field line equations to a one-dimensional time-dependent Hamiltonian system is used to construct magnetic fields with arbitrary toroidal magnetic surfaces I = const. For this purpose Hamiltonians H which together with their invariants satisfy periodicity constraints have to be known. The choice of H fixes the rotational transform η(I). Arbitrary axisymmetric fields, and nonaxisymmetric fields with constant η(I) are considered in detail.Configurations with coinciding magnetic and current density surfaces are obtained. The approach used is not well suited, however, to satisfying the additional MHD equilibrium condition of constant pressure on magnetic surfaces.

Sign in / Sign up

Export Citation Format

Share Document