Peter M.K. Yau and Badrinath Nagarajan McGill University A Numerical Study of a TOGA COARE Super Cloud Cluster – Preliminary results Peter M.K. Yau and Badrinath Nagarajan McGill University

Outline Motivation & Objectives Case Overview Modeling Strategy Results & Conclusions Future work

Motivation MJO associated with supercloud clusters. Processes organizing warm-pool convection a “zeroth-order problem” (Webster & Lucas 1992) Organizing mechanisms (OM) particularely at meso-and synoptic scale not well understood (Yanai et al 2000, Gabrowksi 2003). Improved understanding of OM on various scales should lead to: better representation of convection in models reduced forecast errors at the medium range better representation and understanding of the role of convection on water vapor distribution in the vertical

Objective Use a real data multi-grid (15-5-1 km) numerical modeling approach to simulate supercloud clusters (SCCs) over TOGA COARE diagnose the processes that: organize MCSs, cause clustering of MCSs, and study the impact of convection on water vapor distribution in the vertical

Case Overview – IOP of TOGA COARE OLR (W m-2) Once a day Averaged 5S - 5N OLR < 215 W m-2 Shaded Focus of this study on SCC A 1Nov 92 1Dec 92 1Jan 93 1Feb 93 28 Feb 93 Yanai et al (2000)

The 6 DEC. 92 – 6 JAN. 93 SUPER CLOUDCLUSTER IFA Longitude Time Time cluster MCSs Time cluster: Lifetime > 24 h MCS: Lifetime < 24 h Data Used: Hourly GMS Infrared data 0-10S average Areas < 235 K precipitating (GATE/COARE convection)

EVOLUTION of IFA time cluster (11-13 DEC 92) mm h-1 Data Used: Precipitation retrieved from SSM/I, VIS/IR satellite data Sheu et al (1996), Curry et al (1999) 3 hourly/ 30 km resolution

EVOLUTION of IFA time cluster (11-13 DEC 92) mm/h Data Used: Precipitation retrieved from SSM/I, VIS/IR satellite data Sheu et al (1996), Curry et al (1999) 3 hourly/ 30 km resolution

Schematics of Nakazawa (1988) Madden & Julian (1994)

Propagation of Time Clusters Time cluster: IFA Lifetime > 24 h Time Longitude Time 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Time cluster: Lifetime > 24 h Westward propagating Eastward Propagation of Time Clusters

PROPAGATION OF TIME CLUSTERS 200 hPa IFA Longitude Time 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Westward propagating Eastward propagating

Time Evolution of Domain Average Brightness Temperature Early morning minimum Afternoon minimum (land) Afternoon minimum (ocean)

Brightness temperature minimum occurs: Early morning for 8 time clusters, Afternoon for 4 time clusters Suggests that most of the time clusters are indeed MCSs

Organizing Mechanisms Large scale flow features (e.g., 2-day waves) Vertical wind shear (Le Mone et al 1999) Mid-level mesovortices (Nagarajan et al 2004) – Dec. 15, 1992 Mapes gravity-wave mechanism

1-4, 7-9, 11-13 associated with 2-day wave TIME CLUSTERS & 2-DAY PERIODICITY IFA 1 2 3 4 1-4, 7-9, 11-13 associated with 2-day wave (Chen et. al 1996, Takayabu et. al 1996) 5 6 7 Time 8 9 10 11 12 13 14 15 16 Longitude K Westward propagating Eastward propagating

TIME CLUSTERS & VERTICAL SHEAR* (wind speed) DATE 1000-850 hPa 800-400 hPa 6 – 19 Dec. 92 28 - 31 Dec. 92 1, 4-6 Jan. 93 < 3.0 m s-1 < 5.0 m s-1 20 - 28 Dec. 92 > 3.0 m s-1 > 5.0 m s-1 27 Dec. 92 2-3 Jan. 93 *Areal & Temporal Averages Temporal average: Duration of the time cluster Areal average: 0-10S, longitudinal extent of time cluster

Summary During the lifetime of the SCC (6Dec-6Jan): Identified 16 time clusters consisting of eastward & westward propagating cloud clusters. Convection generally associated with 2-day wave activity Convection occurred in a weak vertical wind shear environment except between 20-28 Dec 1992.

The Model Canadian mc2 model (Benoit et al. 1997) Fully compressible equations Semi-Lagrangian, semi-implicit numerics One-way nesting of lateral boundary conditions RPN1 physics package 1 Recherche en Prevision du Numerique

1-month long time series Time series based on last 24 h of each 27h long simulation. 00 UTC/6 Dec. 92 03UTC/7 Dec. 92 00 UTC/7 Dec. 92 03 UTC/8 Dec. 92 00 UTC/6 Jan. 93 00 UTC chosen because of high availability of rainfall data for assimilation Time integration strategy follows guichard et al. (2003)

MC2 MODEL DOMAIN 3900 km 130E 160E 190E 10N EQ 10S IFA Grid Size: 549 x 279 x 40, Horizontal grid length: 15 km Model Top: 26 km

Modeling Strategy Model Parameters: Initial Conditions: KF CPS (deep convection), BM CPS (shallow convection), Kong and Yau (1997) explicit bulk 2-ice microphysics, time step(90 s) Initial Conditions: ECMWF operational analysis (0.5 o) enhanced: radiosonde data (Cieleski et al 2003), temperature & moisture profiles modified by 1D-VAR rainfall rate assimilation scheme (Nagarajan et al. 2006) and ABL moistening due to diurnal SST warming (Nagarajan et al 2001, 2004). 6-hourly lateral boundary conditions

IFA averaged surface precipitation rate Missing data

IFA averaged surface sensible and latent heat flux

Horizontal size distribution of clouds (Model Domain) Missing data Wielicki & Welch (1986)

Domain-averaged surface precipitation rate (140-180E, 0-10S) Missing data

IFA Av. RH RH Height (km) (h)

Conclusions The IFA-mean and temporal variability of: Large scale : surface fluxes of latent and sensible heat, surface precipitation reasonable Large scale : Simulated surface precipitation overpredicted Horizontal size of cloud clusters are reasonably simulated. Month long mesoscale simulation captures reasonably the life cycle of the super cloud cluster.

Future Work Nesting to higher resolutions (5 km and 1 km) with new three-moment 4 - ice microphysics (Milbrandt and Yau 2005a,b) Diagnose mechanisms that organized the super cloud cluster Diagnose processes for water vapor and temperature distributions