Effects of cloud-radiative forcing on atmospheric response to tropical SST anomaly: Observation and simulation.

摘要

Cloud-climate interannual variations associated with the anomalous SST over the tropical region are investigated by using five-year monthly mean SST, ERBE data and CCM2/AMIP simulation. Cloud effects, in terms of cloud-radiative forcing (CRF), on the atmospheric responses to the tropical SST anomaly, associated with El Nino and the Southern Oscillation (ENSO) event, have been studied by using the NCAR CCM2.;In our simulation, cloud effects intensify the model Southern Oscillation response to the SST anomaly with a negative SLP anomaly in the central-eastern Pacific Ocean and a positive anomaly in the western Pacific-Indian Ocean. Cloud effects produce a warming (cooling) throughout the troposphere and a cooling (warming) at the tropopause in the central-eastern Pacific (western Pacific-Indian Ocean). The zonal wind change associated with the temperature change shows a enhanced model Southern Oscillation with an westerly (easterly) anomaly at low levels and a easterly (westerly) anomaly at high levels in the central-eastern Pacific (western Pacific-Indian Ocean). The cloud effect weakens the intensity of the normal Walker circulation for both the east and west branches.;The longwave heating rate change due to cloud amount change, which is associated with the SST anomaly, presents a warming (cooling) at low levels and a cooling (warming) at high levels in the east (west). This change destabilizes (stabilizes) the troposphere and enhances (suppresses) deep convection and latent heat release in the east (west). The shortwave heating rate change is opposite to the longwave heating rate change and plays an opposite role to the cloud longwave heating as it interacts with deep convection and latent heat release. Cloud has a large impact on the latent heating response to the SST anomaly with a strong warming (cooling) presented in the middle-upper troposphere in the east (west), i.e., cloud effects enhance (suppress) the deep convection in the east (west) with the ENSO type SST anomaly over the central-eastern Pacific.;The convection anomalies in terms of anomalous CRF appear to be in east-west anti-phase dipole patterns with ascending (descending) vertical motion over the central Pacific Ocean and descending (ascending) vertical motion over the maritime continent-South Pacific Convergence Zone (SPCZ) and Brazil for the positive (negative) anomalous SST presented over the central-eastern Pacific Ocean. It is suggested that the opposite type of strong anomalous SST may produce a reverse Walker circulation in the anomalous sense, which could be interpreted as a teleconnection.