Abstract
The impact of the model-output vertical resolution on the moist static
energy (MSE) budget associated with the Madden-Julian Oscillation (MJO)
is examined. To achieve this objective, we perform the MSE budget
analysis employing reanalysis data at different vertical resolutions:
raw output layers, six standard layers as stipulated by the CMIP6 model
requirements, high resolution in the upper troposphere, and high
resolution in the lower troposphere. Results show that the data with
only six layers results in a significant budget residual, consistent
with the CMIP6 models observed. Moreover, the data with high resolution
in the upper troposphere capture more realistic moist processes than
data with high resolution in the lower troposphere. The budget residuals
amplify with the rainfall anomalies and correspond to an overestimated
vertical MSE advection. The leading bias source is associated with a
strong vertical gradient of mean-state dry static energy (DSE) in the
upper troposphere, which interacts with anomalous vertical velocity and
thus leads to more MSE transport. Unrealistic vertical profiles of
mean-state DSE and convection are also observed in the CMIP6 models.
Examination of the same analysis using the DYNAMO field campaign shows
that budget residuals are evident in low vertical resolution data, yet
they correspond to an underestimated vertical MSE advection. The results
from these datasets indicate that existing MSE budget residuals in the
CMIP6 models are partially attributed to the low vertical resolution
data.