Toward a Mesoscale Modeling-Observations Plan for NAME

1
Toward a Mesoscale Modeling-Observations Plan for
NAME
Mitchell W. Moncrieff, NCAR/MMM, Boulder CO
NAME 3rd Science Working Group Meeting, Oct 25th
2002, George Mason University, VA.
2
The context

• Recommendation The U.S. CLIVAR SSC has
  recommended that NAME organizes a Mesoscale
  Modeling-Observations (MM-OBS) team aimed at
  interlinking the mesoscale modeling community
  (especially physical parameterization interests)
  and NAME field measurements. 
• Motivation Contribute to a ramp-up strategy for
  the NAME Field Campaign provide guidance on
  needs and priorities for NAME observations
  identify sustained observational requirements
  identify additional process studies necessary to
  reduce uncertainties and develop partnerships
  between observations and modeling.
• Focus Parallel to the Atmospheric Global
  Circulation ModelObservations (AGCM-OBS) team
  focus on the warm-season diurnal cycle over the
  US and Mexico in AGCMs. 

3
Basic points

• Physical processes on scales order 1 km-100 km
  are fundamental to the diurnal cycle of
  convection.
• Diurnal cycle and the organization of convection
  on mesoscales cannot be legitimately separated.
• Mesoscale processes are not resolved in GCMs,
  not resolved or distorted in NWP models and RMMs
  (the scale-separation issue).
• Mesoscale processes measured by the NAME Tier 1
  observing facilities are represented explicitly
  by cloud-system-resolving models (CSRMs) over a
  similar dynamic range (1 km 100s km).
• Gives prospect for understanding the diurnal
  cycle and the large-scale role of organized
  convection in complex coastal terrain and
  addressing convective parameterization aspects.

4
CSRMs interlink Tier 1 observations, regional
mesoscale modeling and parameterization goals of
the NAME
Parameterization
NAME Tier 1 observations
Regional mesoscale modeling
Cloud-system-resolving models (CSRM)
5

• MM-OBS tasks ltlinkagesgt
• Develop a research strategy complementary to the
  AGCM-OBS Team ltdiurnal cycle of convection in
  complex coastal terraingt
• Define how MM-OBS will complement on-going
  regional mesoscale modeling ltexplicit
  convection, mesoscale observations of surges,
  etc.gt
• Contribute to NAME needs for weather/climate
  prediction  ltparameterization of convection,
  cloud-radiation interaction, effects of terraingt

6
Cross-scale linkages
NAME Tier-1 observations, Cloud-System-
Resolving Models
General Circulation (Climate) Models
7
Over-arching objectives of MM-OBS

• To describe, model and understand the processes
  that determine the diurnal cycle of convection
  and the attendant distribution of precipitation
  in the core region of the NAME.
• To use the explicit cloud-system-resolving model
  approach to improve the representation of
  convection in prediction models, with focus on
  the effects of complex coastal terrain.

8
Specific objectives of MM-OBS

• To describe, model and understand the processes
  that determine the diurnal cycle of convection
  and the mesoscale organization of convection in
  the core region of the NAME.
• To address convective parameterization issues in
  the NAME locale using cloud-system-resolving
  models (CSRM).
• To describe, model and understand the mechanisms
  responsible for the generation of southerly
  surges and low-level jets in the Gulf of
  California.
• To quantify far-field relationships between
  organized convection in the mid-US continent and
  convective cloud systems in NAME Tier 1 region in
  regard to tropical easterly waves and
  mid-latitude westerly troughs.
•  

9
Diurnal cycle and convective organization in NAME

• Processes
• - sea- and land-breeze circulations
• - orographically and convectively
  generated gravity waves
• - propagating, organized convection
  (non-local dynamics)
• - lee vortices in low-Froude-number mean
  flow
• - ITCZ and easterly wave flaring
• - Gulf-surge dynamics
• - far-field influences
• Parameterization
• - convective triggering, transport,
  closure
• - convective organization,
  scale-separation

10
Processes in complex coastal terrain

• Interaction between convectively generated
  gravity waves, terrain and the diurnal cycle of
  convection.
• Lee-effects of thermally forced low Froude number
  flow past complex terrain on the
  location/life-cycle of convection.
• Role of local forcing (surface fluxes,
  quasi-stationary convergence zones, sea-breeze
  and land-breeze circulations).
• Processes that organize convection on the
  mesoscale.
• Dynamics of southerly surges, LLJ in Gulf of
  California in the context of easterly waves and
  convection.
• Far-field influence of the monsoon moisture and
  dynamics on precipitating systems that form over
  Colorado, mod-continental US.

11
Convective triggering sea-breeze dynamics
Crook (2001)
12
Convective triggering low-level flow and shear
Moncrieff and Liu (1999)
13
Orographically and convectively coupled gravity
waves
Mapes et al. (2002)
14
Low-Froude-number lee vortices
Reisner and Smolarkiewicz (1994)
15
Easterly waves and ITCZ flares
TRMM
GOES
16
Gulf surges
Adams and Comrie (1997)
17
Interlinking NAME Tier 1 observations, CSRMs and
parameterization The GATE legacy
18
NAME domains
19
Soundings, radar networks and CSRM simulations
GATE
NAME Tier 1
20
Deployment Issues
Squall system
 
21
Convection and easterly waves the GATE simulation

• CSRMs have simulated convection over tropical
  oceans and in association with major multiscale
  field-programs GATE and TOGA COARE.
• Large-scale forcing prescribed from objectively
  analyzed data from network of tropospheric
  soundings.
• Results used for evaluation/development of
  physically based parameterization of convection
  and cloud-interactive radiation.
• This multiscale cloud-system simulation is
  feasible for the NAME Tier 1 domain in the
  challenging physical setting of complex coastal
  terrain.

22
Easterly-wave-modulated convection

• Synoptic-scale baroclinic variability
  (large-scale forcing, shear) by easterly waves
  controlled the organization of convection in GATE
  over a 1-week period.
• CSRM used to study this aspect and attendant
  parameterization issues using large-scale forcing
  derived from GATE sounding network.
• Similar strategy could be used for NAME Tier 1,
  complex coastal terrain an extra challenge.

23
(No Transcript)
24
Convection and GATE easterly waves A snapshot
25
CSRM convective mass fluxes
Grabowski et al. (1998)
26
CSRM clouds and radiation
27
Interlinking RMMs and CSRMs Hierarchical modeling
CSRM
Kain-Fritsch

• In the hierarchical approach, CSRM
  parameterizations are run using the same
  non-hydrostatic dynamical core but at different
  resolution.
• Left CSRM run at 2-km grid resolution.
• Right Kain-Fritsch (K-F) parameterization at
  15-km grid-resolution.

• Liu et al. (2000)

28
CSRM-derived parameterization issues

• Overly deep convection and extensive cirrus a
  result of excessive detrainment of condensate.
• Sensitivity to grid-scale moisture feedback from
  convective parameterization.
• Parameterized overshoot-generated adiabatic
  cooling at cloud tops too strong, resulting in
  cold bias.
• Over-prediction of low-level moisture attributed
  to parameterized downdrafts.
• These shortcomings stem from the single-plume
  model used in the parameterization, which does
  not represent the trimodal distribution of
  cumulonimbus, congestus, and shallow convection
  observed by Johnson et al. (1999) and simulated
  by the CSRM.

29
Easterly waves, ITCZ moist flares in TRMM
monthly composites
30
Far-field influences
Saleeby and Cotton (manuscript)
31
Liu and Moncrieff (2003)
32
Total condensate
18 UTC 12 MDT
00 UTC 18 MDT
06 UTC 00 MDT
12 UTC 06 MDT
33
Conclusion

• Key point CSRMs can integrate the observational
  and parameterization objectives and the mesoscale
  and large-scale objectives of the NAME.
• Use of CSRMs in convective parameterization
  development developed over a number of years by
  international GEWEX Cloud System Study (GCSS) and
  also by individual efforts.
• Field-observation/CSRM collaboration a legacy of
  GATE and TOGA COARE field programs.
• Complex coastal terrain of NAME a challenging
  next step in collaborative observational-modeling
  efforts.
• Evaluation of CSRMs an intensive activity,
  relying on the NAME Field Program design (e.g.,
  sounding network, radar, lidar) and post-field
  analysis (mesoscale, cloud-scale)