Sensitivity of MJO to the CAPE lapse time in the NCAR CAM3.1 Ping Liu, Bin Wang International Pacific Research Center University of Hawaii Sponsored by SciDAC project, computations partly finished at SDSC Thanks to: Jerry Meehl 2007 CCSM AMWG meeting at NCAR

In CAM3.1 T42L26, MJO is weak in amplitude and irregular in propagation as in CCM3 (Maloney 2001) and CAM2 (Liu et al 2005)

Variance of day filtered U850 in extended winter season (NDJFMA) during

Variance of day filtered precipitation in extended winter season (NDJFMA) during

Variance of day filtered OLR in extended winter season (NDJFMA) during

Power spectra (10N-10S) Winter Nov-Apr 850hPa u

Power spectra (10N-10S) Winter Nov-Apr OLR

Irregular Regression of U850 Onto 155E in Extended winter During With filtered data

Why? Observational studies indicate a close coupling exists between large-scale disturbances and convection associated with MJO (Wang 1988, …) A precondition of moisture (or buildup) by boundary layer convergence and/or shallow convection before deep convection associated with MJO bursts (Hendon, Salby, Maloney, Sperber…)

Why? Experiments with CCM3 (Maloney 2001, Zhang 2005) and CAM2 (Liu 2005) disclose that either model with alternative convective schemes or a revised closure can simulate much improved MJO although deficiencies remain Consequently the convective schemes probably have flaws in 1) deep convection configuration; 2) partition of deep/shallow convection

Where? Basic theories in the Zhang and McFarelane (1995) scheme for deep convection (1) A mass flux scheme based on Quasi-Equilibrium theory (Arakawa and Schubert 1974) (2) Uniform mass flux at cloud base for updraft (3) Convection is triggered wherever there is net positive CAPE (including CIN). Or CAPE threshold is positive (70 J/kg in code). (4) Scheme closed on CAPE consumed exponentially at a specified time scale (2 hours in paper, 1 hour in code: tau=3600.).

Hypothesis “Convection frequently occurs pre-maturely in the CCSM2” (Dai 2004). Add a RH threshold for triggering deep convection can enhance the precipitation variability (Zhang and Mu 2005) but not for the RAS (Maloney 2001) in CCM3. A too frequent deep convection might prevent a reasonabe partition of shallow/deep convection then moisture buildup does not occur. So (3) Is the CAPE threshold low? The QE theory requires (4) the specified time for CAPE lapse too short?

More evidence “Tropical atmosphere have a thermal-dynamical background of CAPE at 1000 J/kg” – Heat engine theory by Renno (1996; reversible) Zhang and McFarelane (1995) table

LTM ( ) DJFM Pseudo-Adiabatic CAPE, J/kg interval 500, thick 1500

Experiments CAPE threshold: 3 and 10 times CAPE lapse time: 1, 2, 4, 6, 8, 10 hours Run: AMIP ~ Model: CAM3.1 T42L26

Results CAPE threshold: 3 and 10 times 210, 700 J/kg

LTM ( ) DJFM P-A (left) and RV (right) CAPE, J/kg

LTM ( ) DJFM precipitation, mm/day Interval 3, thick 9

Regression of U850 Onto 155E in Extended winter During With filtered data

Indications from CAPE threshold experiments Lifting the CAPE threshold to 10 times as large as that in control can help the mean state and MJO to some extent, but obviously cannot significantly improve the structure of MJO.

Results CAPE lapse time: 4, 6, 8, 10 hours

LTM ( ) DJFM Reversible CAPE, J/kg interval 200, thick 800

LTM ( ) DJFM Pseudo-Adiabatic CAPE, J/kg interval 500, thick 1500

LTM ( ) DJFM precipitation, mm/day Interval 3, thick 9

LTM ( ) DJFM Reversible CAPE, J/kg interval 200, thick 800

Power spectra (10N-10S) Winter Nov-Mar 850hPa u

Power spectra (10N-10S) Winter Nov-Mar OLR

MJO based on ZM8HR

Variance of day filtered U850 in extended winter season (NDJFMA) during

Variance of day filtered precipitation in extended winter season (NDJFMA) during

Variance of day filtered precipitation in extended winter season (NDJFMA) during

Regression of U850 Onto 155E in Extended winter During With filtered data

Frictional convergence in a composite MJO life cycle Maloney (1998; 2001) Liu (2005)

NOAA ZM8HR First two EOFs of 10N~10S mean filtered OLR

Power spectra (10N-10S) Winter Nov-Mar OLR

Power spectra (10N-10S) Winter Nov-Mar OLR

Partitioning of shallow and deep convection

LTM ( ) DJFM ratio of shallow convective to total precipitation Interval 10%, shaded >= 50%

LTM ( ) DJFM ratio of shallow (left) and deep (right) convective to total precipitation Interval 10%, shaded >= 50%

Summary. Lifting the CAPE threshold does not significantly improve MJO. Lengthening the CAPE lapse time enhances MJO variability and improves its structure.. The CAPE lapse time is optimal at 8 hours to simulate the MJO in both variability and structure. Frictional convergence mechanism functions from the Indian Ocean to western Pacific, which is close to observational facts. A 4:5 partition of shallow and deep convection is a key feature in this case.. ZM8HR is an ideal starting point for further work.

Future work Local CAPE lapse time Standard plots for ZM8HR based on AMWG packages 1 and 2, please see