2:25 PM - 2:40 PM
[AAS01-04] A statistical analysis on convectively coupling mechanisms of equatorial Rossby and Kelvin waves based on satellite observations.
Keywords:Equatorial Waves, Moist Convection
We make composite analysis of synoptic scale wave disturbances and convective activities. Kelvin waves show tri-modal convective evolution: shallow cumuli, deep and isolated convections, and organized MCSs with stratiform precipitation, highly corresponds to gravity wave-like structures. Rossby wave show direct transition from shallow cumuli to organized MCSs, with vertically upright structure and well stacked column water vapor (CWV). These features can be observational evidence for convectively coupling of gravity-wave mode and moisture mode.
We define wave phase based on FFT-filtered brightness temperature. Composite synoptic disturbances are from reanalysis data, ERA5. Precipitation amount, its characteristics and apparent heat source and moisture sink are quantified based on rainfall-event dataset, which is defined using TRMM level2 product. CWV and surface wind speed are estimated from SSM/I observation. We jointly use these satellite data and make composite analysis referring to wave phase.
In case of Rossby waves, a vertically upright structure and its upright vortices induce large amplitude of CWV anomalies. Precipitation activity is almost in phase with CWV and its characteristics do not vary drastically over a half wavelength. Shallow cumulus activity leads along the equator, spreads toward off-equatorial regions, and directly transits into well-organized systems, which contribute large precipitation amount.
In case of Kelvin waves, a gravity wave-like structure is indicated. Specific humidity develops from near the surface to middle troposphere as the wave phase progresses. A clear negative CWV anomaly does not exist despite the existence of negative precipitation anomalies. As in phase with this moisture evolution, tri-modal convective evolution is dominant. Shallow cumuli are highly active in the phase of moist layer near the surface with lower precipitation. Deep but nor organized cumulonimbus are dominant where the lower troposphere is moist, and the middle troposphere is dry. Heavy precipitation is contributed by well-organized systems where deep moist layer. This convective evolution induces a latent hear release profile that tends from bottom-heavy to top-heavy, and corresponds well with the gravity wave-like structure and modulates the phase relation between temperature and vertical motion.
For both wave cases, apparent heat sources can amplify available potential energy despite of the difference of instability modes of these two waves; precipitation is driven by CWV fluctuation for Rossby wave case, and by dynamical disturbances for Kelvin wave case. Furthermore, shallow cumuli may have a role for moisten lower free troposphere and may be a factor for propagation of precipitation for both waves. These results can be an observational evidence of actual coupling process that is comparable to previous idealized studies.
We define wave phase based on FFT-filtered brightness temperature. Composite synoptic disturbances are from reanalysis data, ERA5. Precipitation amount, its characteristics and apparent heat source and moisture sink are quantified based on rainfall-event dataset, which is defined using TRMM level2 product. CWV and surface wind speed are estimated from SSM/I observation. We jointly use these satellite data and make composite analysis referring to wave phase.
In case of Rossby waves, a vertically upright structure and its upright vortices induce large amplitude of CWV anomalies. Precipitation activity is almost in phase with CWV and its characteristics do not vary drastically over a half wavelength. Shallow cumulus activity leads along the equator, spreads toward off-equatorial regions, and directly transits into well-organized systems, which contribute large precipitation amount.
In case of Kelvin waves, a gravity wave-like structure is indicated. Specific humidity develops from near the surface to middle troposphere as the wave phase progresses. A clear negative CWV anomaly does not exist despite the existence of negative precipitation anomalies. As in phase with this moisture evolution, tri-modal convective evolution is dominant. Shallow cumuli are highly active in the phase of moist layer near the surface with lower precipitation. Deep but nor organized cumulonimbus are dominant where the lower troposphere is moist, and the middle troposphere is dry. Heavy precipitation is contributed by well-organized systems where deep moist layer. This convective evolution induces a latent hear release profile that tends from bottom-heavy to top-heavy, and corresponds well with the gravity wave-like structure and modulates the phase relation between temperature and vertical motion.
For both wave cases, apparent heat sources can amplify available potential energy despite of the difference of instability modes of these two waves; precipitation is driven by CWV fluctuation for Rossby wave case, and by dynamical disturbances for Kelvin wave case. Furthermore, shallow cumuli may have a role for moisten lower free troposphere and may be a factor for propagation of precipitation for both waves. These results can be an observational evidence of actual coupling process that is comparable to previous idealized studies.