scholarly journals Zonally Symmetric Adjustment in the Presence of Artificial Relaxation

2014 ◽  
Vol 71 (11) ◽  
pp. 4349-4368 ◽  
Author(s):  
Peter Hitchcock ◽  
Peter H. Haynes
Keyword(s):  
Boundary Condition ◽  
General Circulation ◽  
Circulation Model ◽  
Companion Paper ◽  
Reference State ◽  
Effective Boundary ◽  
Effective Boundary Condition ◽  
Meridional Mass Circulation ◽  
Sponge Layer ◽  
Mass Circulation

Abstract Numerical experiments, presented in a companion paper, have been performed in which the zonal-mean state of the stratosphere in a comprehensive, stratosphere-resolving, general circulation model is strongly relaxed (or “nudged”) toward the evolution of a reference sudden warming event in order to investigate its influence on the freely evolving troposphere below. Similar approaches have been used in a number of other studies. This raises the question of whether such an artificial relaxation induces the adiabatic and diabatic adjustments expected below the region of nudging, even in the absence of the stratospheric wave driving responsible for the reference event. Motivated by this question, the zonally symmetric quasigeostrophic diabatic response to zonal forces (representing wave driving) in a system nudged to a time-dependent reference state is studied. In the presence of wave driving in the nudging region that differs from the reference state, the meridional mass circulation of the reference state is reproduced only in the region below the nudging up to a correction that is inversely proportional to the strength of the nudging. The anomalous circulation is confined because of an effective boundary condition at the interface of the nudging layer. The nudging also produces an artificial “sponge-layer feedback” immediately below the region of the nudging in response to differences in the tropospheric wave driving. The strength of this artificial feedback is closely related to the strength of the effective boundary condition; however, the time scale required for the sponge-layer feedback to be established is typically much longer than that required for the confinement.

scholarly journals Leaky Rigid Lid: New Dissipative Modes in the Troposphere

2013 ◽  
Vol 70 (10) ◽  
pp. 3119-3127 ◽  
Author(s):  
Lyubov G. Chumakova ◽  
Rodolfo R. Rosales ◽  
Esteban G. Tabak
Keyword(s):  
Boundary Condition ◽  
Radiation Condition ◽  
Wave Radiation ◽  
Pseudodifferential Equation ◽  
Piecewise Constant ◽  
Effective Boundary ◽  
Propagating Waves ◽  
Effective Boundary Condition ◽  
Set Up ◽  
Atmospheric Phenomena

Abstract An effective boundary condition is derived for the top of the troposphere, based on a wave radiation condition at the tropopause. This boundary condition, which can be formulated as a pseudodifferential equation, leads to new vertical dissipative modes. These modes can be computed explicitly in the classical setup of a hydrostatic, nonrotating atmosphere with a piecewise constant Brunt–Väisälä frequency. In the limit of an infinitely strongly stratified stratosphere, these modes lose their dissipative nature and become the regular baroclinic tropospheric modes under the rigid-lid approximation. For realistic values of the stratification, the decay time scales of the first few modes for mesoscale disturbances range from an hour to a week, suggesting that the time scale for some atmospheric phenomena may be set up by the rate of energy loss through upward-propagating waves.

scholarly journals Effective boundary condition for Stokes flow over a very rough surface

2013 ◽  
Vol 254 (8) ◽  
pp. 3395-3430 ◽  
Author(s):  
Youcef Amirat ◽  
Olivier Bodart ◽  
Umberto De Maio ◽  
Antonio Gaudiello
Keyword(s):  
Boundary Condition ◽  
Rough Surface ◽  
Stokes Flow ◽  
Effective Boundary ◽  
Effective Boundary Condition

Two-phase displacement in Hele Shaw cells: theory

1984 ◽  
Vol 139 ◽  
pp. 291-308 ◽  
Author(s):  
C.-W. Park ◽  
G. M. Homsy
Keyword(s):  
Boundary Condition ◽  
Asymptotic Expansion ◽  
Asymptotic Expansions ◽  
Characteristic Length ◽  
Two Phase ◽  
Phase Displacement ◽  
Effective Boundary ◽  
Small Parameters ◽  
Effective Boundary Condition ◽  
Gap Width

A theory describing two-phase displacement in the gap between closely spaced planes is developed. The main assumptions of the theory are that the displaced fluid wets the walls, and that the capillary number Ca and the ratio of gap width to transverse characteristic length ε are both small. Relatively mild restrictions apply to the ratio M of viscosities of displacing to displaced fluids; in particular the theory holds for M = o(Ca−1/3). We formulate the theory as a double asymptotic expansion in the small parameters ε and Ca1/3. The expansion in ε is uniform while that in Ca1/3 is not, necessitating the use of matched asymptotic expansions. The previous work of Bretherton (1961) is clarified and extended, and both the form and the constants in the effective boundary condition of Chouke, van Meurs & van der Poel (1959) and of Saffman & Taylor (1958) are determined.

scholarly journals On improving the ability of a high-resolution atmospheric general circulation model for dynamical seasonal prediction of the extreme seasons of the Indian summer monsoon

MAUSAM ◽  
2021 ◽  
Vol 62 (3) ◽  
pp. 339-360
Author(s):  
D.R. SIKKA ◽  
SATYABANBISHOYI RATNA
Keyword(s):  
Boundary Condition ◽  
High Resolution ◽  
Summer Monsoon ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Monsoon Season ◽  
Circulation Model ◽  
Seasonal Prediction ◽  
Atmospheric General Circulation ◽  
Dynamical Seasonal Prediction

The paper is devoted to examine the ability of a high-resolution National Center for Environmental Prediction (NCEP) T170/L42 Atmospheric General Circulation Model (AGCM), for exploring its utility for long-range dynamical prediction of seasonal Indian summer monsoon rainfall (ISMR) based on 5-members ensemble for the hindcast mode 20-year (1985-2004) period with observed global sea surface temperatures (SSTs) as boundary condition and 6-year (2005-2010) period in the forecast-mode with NCEP Coupled Forecast System (CFS) SSTs as boundary condition. ISMR simulations are examined on five day (pentad) rainfall average basis. It is shown that the model simulated ISMR, based on 5-members ensemble average basis had limited skill in simulating extreme ISMR seasons (drought/excess ISMR). However, if the ensemble averaging is restricted to similar ensemble members either in the overall run of pentad-wise below (B) and above (A) normal rainfall events, as determined by the departure for thethreshold value given by coefficient of variability (CV) for the respective pentads based on IMD observed climatology, or during the season as a whole on the basis of percentage anomaly of ISMR from the seasonal climatology, the foreshadowing of drought/excess monsoon seasons improved considerably. Our strategy of improving dynamical seasonal prediction of ISMR was based on the premise that the intra-seasonal variability (ISV) and intra-annual variability (IAV) are intimately connected and characterized by large scale perturbations westward moving (10-20 day) and northward moving (30-60 day) modes of monsoon ISV during the summer monsoon season. As such the cumulative excess of B events in the simulated season would correspond to drought season and vice-versa. The paper also examines El Niño-Monsoon connections of the simulated ISMR series and they appear to have improved considerably in the proposed methodology. This strategy was particularly found to improve for foreshadowing of droughts. Based on results of the study a strategy is proposed for using the matched signal for simulated ISMR based on excess B over A events and vice-versa for drought or excess ISMR category. The probability distribution for the forecast seasonal ISMR on category basis is also proposed to be based on the relative ratio of similar ensemble members and total ensembles on percentage basis. The paper also discusses that extreme monsoon season are produced by the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) modes in a combined manner and hence stresses to improve prediction of IOD mode in ocean-atmosphere coupled model just as it has happened for the prediction ENSO mode six to nine months in advance.

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