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Lab for Atmospheric Dynamics

<Convective Gravity Waves>

 

Momentum flux of convective gravity waves derived from an off-line gravity wave parameterization

 

Gravity waves (GWs) transfer momentum and energy of the atmosphere from the troposphere to the stratosphere and mesosphere. Among the various sources of GWs, convectively generated gravity waves (CGWs) have a broad spectrum and can thus transport their momentum through the mean flow throughout all seasons.

 

The small-scale gravity waves with horizontal wavelengths of few tens of kilometers are neither detected from global observation, such as satellite data, nor fully represented by high-resolution general circulation models with horizontal grid spacing of ~0.25°. In this respect, CGW momentum flux and drag using a physically based and source-dependent parameterization and global reanalysis data are created recently (Kang et al. 2017).

 

 

Fig. 1a.pngFig. 2a.png

Fig. 1b.pngFig. 2b.png

 

<Global distributions of column-maximum deep convective heating rate (left)

and cloud-top gravity wave momentum flux (CTMF, right) in (a) January and (b) July>

 

 

 

The cloud-top (source-level) convective gravity wave momentum flux (CTMF) is not solely proportional to the magnitude of deep convective heating rate (DCH) but is affected by the wave-filtering and resonance factor and background stability and temperature underlying the convection, which results in the different latitudinal distribution of DCH and CTMF.

 

The dataset can be utilized to study such relationship, as the results provide the full vertical information of GW quantities above the tropospheric convection associated with the Madden-Julian Oscillation (MJO), quasi-biennial oscillation (QBO), and El niño and Southern Oscillation (ENSO).

 

Reference:

Kang, M.-J., H.-Y. Chun, and Y.-H. Kim, 2017: Momentum flux of convective gravity waves derived from an off-line gravity wave parameterization. Part Ι: Spatiotemporal variations at source level. J. Atmos. Sci., in review.

 

 

The difference of Convective Activities and CGW in Tropics Region by Quasi Biennial Oscillation

 

Quasi-biennial oscillation (QBO), the oscillation of stratospheric zonal wind (westerly and easterly) with a period averaging 28~29 months, is the most prominent variability in the tropical stratosphere. This phenomenon is related to wave activity classified into large-scale equatorial wave modes and mesoscale gravity waves.

 

QBO significantly affects the tropical troposphere. According to plumb and bell [1982], anomalous meridional circulation of QBO easterly phase (QBOE) intensifies (weakens) convective activity in tropics (subtropics). An opposite result occurs in QBO westerly phase (QBOW).

 

페이지_ gravity.jpg

 

The composites of convective activities by each QBO phase using 5 metrics are as follows.Fig.2.png

The conclusion from above figure is that the difference of convective activity according to the opposite QBO phase can be determined by the longitudinal difference related to the bias of Hadley and Walker circulation.

In the future, we will investigate difference of convective gravity waves according to each QBO phase using two-dimensional ideal simulation (WRF).

 

Reference.

Plumb, R. A., and R. C. Bell, 1982: A model of the quasi-biennial oscillation on an equatorial beta-plane. Quart. J. Roy. Meteor. Soc., 108, 335–352.

 

 

Interaction of Gravity Waves and Madden-Julian Oscillation

 

The tropics as a dynamical system play an important role in the vertical coupling of the atmosphere due to the prominent convection and the resulting upwelling of air masses. In the tropical troposphere the Madden-Julian- Oscillation (MJO) (Madden and Julian, 1972) plays an important role and influences local weather systems. The MJO consists of clusters of increased and decreased convection which arise in the western Indian Ocean and propagate eastward deep into the Pacific Ocean. This results in periods of severely increased localized precipitation.

 

Fig. 1.png

 

 

 

Even though the MJO has been investigated for several decades, prediction skills of atmospheric models still lack sophistication. Hence, improvement in forecast skill of state-of-the-art weather models  is required. In this project, we investigate the influence of short scale gravity wave activity from MJO convection. Gravity waves transport large amounts of momentum and energy from their sources to remote areas in the atmosphere and may travel several thousand kilometers until they dissipate in the middle-to-upper atmosphere. It is therefore crucial for understanding of MJO dynamics to properly model excitation, propagation, and dissipation of gravity waves.

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