TY - JOUR
T1 - Multiscale waves in an MJO background and convective momentum transport feedback
AU - Khouider, Boualem
AU - Han, Ying
AU - Majda, Andrew J.
AU - Stechmann, Samuel N.
PY - 2012/3
Y1 - 2012/3
N2 - The authors use linear analysis for a simple model to study the evolution of convectively coupled waves (CCWs) in a background shear and background moisture mimicking the observed structure of the Madden- Julian oscillation (MJO). This is motivated by the observation, in an idealized setting, of intraseasonal twoway interactions between CCWs and a background wind. It is found here that profiles with a bottom-heavy moisture content are more favorable to the development of mesoscale/squall line-like waves whereas synoptic-scale CCWs are typically more sensitive to the shear strength. The MJO envelope is thus divided into three regions, in terms of the types of CCWs that are favored: an onset region in front that is favorable to Kelvin waves, a mature or active region in the middle in which squall lines are prominent, and the stratiform and decay phase region in the back that is favorable to westward inertia-gravity (WIG) waves. A plausible convective momentum transport (CMT) feedback is then provided according to the results of the idealized two-way interaction model. The active region, in particular, coincides with the westerly wind burst where both Kelvin waves and squall lines are believed to play a significant role in both the deceleration of low-/high-level easterly/westerly winds and the acceleration of low-/high-level westerly/easterly winds. The WIG waves in the wake could be a precursor for a subsequent MJO event through the acceleration of low-/high-level easterly/ westerly winds, which in turn favor Kelvin waves, and the cycle repeats. These results open interesting directions for future studies using observations and/or detailed numerical simulations using the full primitive equation.
AB - The authors use linear analysis for a simple model to study the evolution of convectively coupled waves (CCWs) in a background shear and background moisture mimicking the observed structure of the Madden- Julian oscillation (MJO). This is motivated by the observation, in an idealized setting, of intraseasonal twoway interactions between CCWs and a background wind. It is found here that profiles with a bottom-heavy moisture content are more favorable to the development of mesoscale/squall line-like waves whereas synoptic-scale CCWs are typically more sensitive to the shear strength. The MJO envelope is thus divided into three regions, in terms of the types of CCWs that are favored: an onset region in front that is favorable to Kelvin waves, a mature or active region in the middle in which squall lines are prominent, and the stratiform and decay phase region in the back that is favorable to westward inertia-gravity (WIG) waves. A plausible convective momentum transport (CMT) feedback is then provided according to the results of the idealized two-way interaction model. The active region, in particular, coincides with the westerly wind burst where both Kelvin waves and squall lines are believed to play a significant role in both the deceleration of low-/high-level easterly/westerly winds and the acceleration of low-/high-level westerly/easterly winds. The WIG waves in the wake could be a precursor for a subsequent MJO event through the acceleration of low-/high-level easterly/ westerly winds, which in turn favor Kelvin waves, and the cycle repeats. These results open interesting directions for future studies using observations and/or detailed numerical simulations using the full primitive equation.
KW - Atmospheric
KW - Convective parameterization
KW - Madden-Julian oscillation
KW - Squall lines
KW - Tropical variabilty
KW - Waves
KW - Wind shear
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U2 - 10.1175/JAS-D-11-0152.1
DO - 10.1175/JAS-D-11-0152.1
M3 - Article
AN - SCOPUS:84863396318
SN - 0022-4928
VL - 69
SP - 915
EP - 933
JO - Journal of the Atmospheric Sciences
JF - Journal of the Atmospheric Sciences
IS - 3
ER -