Embedding a one-column ocean model in CAM5 for improving low-resolution MJO simulations
Abstract
The impact of air-sea interaction on Madden-Julian oscillation (MJO) was investigated with the Community Atmosphere Model (CAM5) coupled to a one-column SIT (Snow/Ice/Thermocline) ocean model. The SIT embedding in CAM5 (CAM5-SIT) is developed to simulate high-resolution vertical mixing u-current, v-current, water temperature and salinity within 10-m depth and mid-resolution from 10-m depth down to the abyss. A more elaborate parameterization of vertical-mixing processes by the turbulent kinetic energy (TKE) equation provides realistic simulations of the turbulent mixing with a reasonable computational efficiency. Weak winds and large insolation resulted in SCAM a shallow mixed layer and large SST diurnal cycles at TOGA COARE during the IOP periods. By contrast, the strong wind (> 10 m/s) erroneously enhances mixed layer deepening and surface temperature cooling. Diurnal SST variation will strengthen the diurnal moistening in atmosphere and both are potential sources of MJO predictability. Time-evolving SST with a diurnal cycle strongly influences the onset and intensity of MJO convection. CAM5-SIT with half-hour coupling frequency significantly improves the MJO simulation over CAM5 with prescribed SST, fully coupled with Slab Ocean Model and with pop2 in wavenumber-frequency spectra of equatorial 850 hPa zonal wind (U850). The mean state SST and eastward propagating U850 and precipitation of CAM5-SIT results are similar to the observations. Using CAM5-SIT, the Rossby number of outgoing longwave radiation in wavenumber-frequency cross-spectra is weaker than observation, which is due to large-scale perturbation. The model distribution at high frequency and small-scale perturbation scheme in Kelvin wave are wider than observation. The coupled model experiments clearly demonstrate the importance of the diurnal SST in MJO eastward propagation. Keywords: Madden-Julian oscillation; CAM5-SIT; turbulent kinetic energy; SST; TOGA COARE
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2015
- Bibcode:
- 2015EGUGA..17.8251L