Properties of convective gravity waves derived by combining global modeling and satellite observations
Trinh
Quang Thai
Trinh, Quang Thai
aut
2016-04-28
2016-07-26
en
<p> Gravity waves play the key role in the dynamics of the middle atmosphere.
Among different gravity wave sources, convection has been long accepted as one
of the most prominent ones. However, due to the broad spectrum of convective
gravity waves and limitations of current observation techniques, the contribution
of these waves to atmospheric dynamics is still an open issue. Moreover, due
to the same reasons, the horizontal and temporal scales of gravity waves forced
by convection are not well known. These scales are usually treated in current
convective gravity wave parameterizations as free parameters and they are defined
by assuming typical scales of convective systems. In this study, we addressed
these issues using a unique approach of combining modeling and measurements.
In order to determine the scales of convective gravity waves, instead of assuming
typical scales of convective systems, a systematic survey varying the spatial and
temporal scales as free parameters of the Yonsei convective gravity wave source
(CGWS) scheme is performed. Gravity waves are generated using this CGWS
scheme and propagated upward using the Gravity wave Regional Or Global RAy
Tracer (GROGRAT). Gravity wave momentum flux spectra in terms of horizontal
and vertical wave numbers are calculated from simulations and compared with
the respective spectrum observed by the High Resolution Dynamics Limb Sounder
(HIRDLS). Based on this comparison, combinations of scale sets which reproduce
the observed gravity wave spectrum are selected.<br>
HIRDLS can only see a limited portion of the gravity wave spectrum due to
visibility effects and observation geometry. To allow for a meaningful comparison
of simulated gravity waves to observations a comprehensive filter that mimics the
instrument limitations is applied to the simulated waves. This comprehensive
observational filter takes into account both instrument visibility due to radiative
transfer and retrieval as well as the complex observation geometry.<br>
In order to analyze the contribution of convective gravity waves to the atmospheric
dynamics, the zonal momentum balance is considered in vertical cross
sections of gravity wave momentum flux (GWMF) and gravity wave drag (GWD),
and consistency between model results and HIRDLS observations is found. Global
maps of the horizontal distribution of GWMF are considered and good agreement
in the structure as well as the magnitude between simulated results and HIRDLS
observations is found. In particular, main convection hot spots are well reproduced.
In addition, the latitude dependence of the zonal phase speed spectrum
of GWMF and its change with altitude is shown. The latitude dependences for
different climate conditions and different altitudes show a main peak in the tropics
and summer subtropics associated with eastward phase speeds between several
m/s and about 30 m/s.<br>
The current study is unique in two aspects: the complexity and comprehensiveness
of the observational filter and the fact that the model spectral distribution
is determined merely from observed spectral distributions. In advance to previous
studies, the spatial distribution is used only afterwards for validation. Due to the
limitation of HIRDLS instrument, only long horizontal wavelength waves are addressed
in the current approach. However, the momentum flux of these waves are
found to be significant and relevant for the driving of the Quasi-Biennial Oscillation
(QBO). Findings of the current study therefore provide the key information
for estimating relative contributions of different convective gravity wave scales to
the whole convective gravity wave spectrum.
urn:nbn:de:hbz:468-20160726-104957-2
2016-07-26T08:39:41.607Z
2016-07-26T08:54:16.414Z
published
Diss
fbc/physik/diss2016/trinh