@InProceedings{SilvaDiasRaupRamiRaph:2017:CoTrDi,
author = "Silva Dias, Pedro L. and Raupp, Carlos F. M. and Ramirez
Gutierrez, Enver Manuel Amador and Raphaldini, Breno",
affiliation = "{Univesidade de S{\~a}o Paulo (USP)} and {Univesidade de S{\~a}o
Paulo (USP)} and {Instituto Nacional de Pesquisas Espaciais
(INPE)} and {Univesidade de S{\~a}o Paulo (USP)}",
title = "Connecting tropical diurnal variability to the decadal and longer
time scales through nonlinear resonance",
year = "2017",
organization = "Conference on Atmospheric and Oceanic Fluid Dynamics 19th
Conference on Middle Atmosphere, 21.",
abstract = "Tropical convection is characterized by strong spectral peaks in
some well defined frequency bands and numerical models do not
always realistically reproduce the observed power. Our goal is to
explore the role of nonlinear resonance as a plausible mechanism
to promote energy transfer from higher frequencies (e.g. the
diurnal scale) to synoptic, intraseasonal, interannual and longer
time scales. The presentation will explore highlights of the
papers published by the authors, discuss some recent advances both
from the point of view of the role of non-hydrostatic processes
and the interaction between the periodic solar forcing and the
resonating triads in the decadal and longer timescales. This work
was initially motivated by the numerical evidence in the late 90s
that models with stronger diurnal variation had a stronger signal
in the intraseasonal band. Non-linear resonance was invoked as a
potential mechanism to explain the connection between the diurnal
and intraseasonal variability in tropical convection. Numerical
integrations of the resonant three-wave problem show that the
energy of the waves in a resonant triad evolves periodically in
time, with the period and amplitude of the energy oscillations
dependent on the magnitude of the initial amplitudes of the waves
and the way in which the initial energy is distributed among the
triad components. The high-frequency modes are found to be
energetically more active than the low-frequency modes. The latter
tend to act as catalytic components in a resonant triad.
Integrations of the problem of two resonant triads coupled by a
single mode point out the importance of gravity waves in the
intertriad energy exchanges, suggesting the significance of these
modes in the redistribution of energy throughout the atmospheric
motion spectrum. The results also show that the inter-triad energy
exchanges provided by the highest frequency mode of two triads
occur in a longer time-scale than the intra-triad interactions.
Therefore, these results also suggest the importance of the
high-frequency modes in the generation of the low-frequency
variability (intraseasonal and even longer term) of the
atmospheric flow. Later, the full primitive equation model was
decomposed in vertical modes and the nonlinear interaction between
internal modes and the external mode were explored. In this case,
it was shown that a Rossby wave associated with the baroclinic
basic state, resonant with the stationary component of the daytime
heat source, and two dispersive modes, given by Mixed
Rossby-gravity wave and a slow barotropic mode (Rossby) may
interact and provoke vacillation in the time scale of many days
(between intraseasonal and interannual time scales). The
importance of the fast modes in the resonant triplets raises the
following question: what is the role of diurnal variation in the
generation of these fast modes? We have also shown, for example,
that a Rossby wave associated with the baroclinic (i.e.,
associated with an internal mode) basic state, resonant with the
stationary component of the daytime heat source, and two
dispersive modes, given by Mixed Rossby-gravity wave and a slow
barotropic mode (Rossby) may interact and provoke vacillation in
the time scale of several days (between intraseasonal and
interannual). Another class of resonant modes is identified with
the interaction between two internal modes of gravity generated by
the diurnal forcing with clear manifestation in the intraseasonal
scale. A generalization of the previous results on the role of the
diurnal forcing was also developed in the context of a heat source
parameterized by the simplest form according to the hypothesis
that the heat source intensity is proportional to the low level
moisture convergence. The study was developed in the context of a
two-layer model that allows interaction between the external
(barotropic) mode and the internal (baroclinic) mode. It
introduces a forcing that has meridional dependence and,
therefore, it becomes feasible to explore the non-linear resonance
involving the interaction of only two waves. The reduced dynamics
of the two-layer model shows that a Rossby mode is significantly
modulated in longer time scales when interacting with an internal
gravity mode (interannual to the decadal scale). More recently we
have explored a simplified multi-scale atmosphere-ocean coupled
model for studying the interactions between
synoptic-intraseasonal-interannual scales. Two coupled nonlinear
equatorial beta-plane shallow water equations are considered: one
for the ocean and the other for the atmosphere. The nonlinear
terms are the intrinsic advective nonlinearity and the
atmosphere/ocean coupling. Simplified parameterizations for the
air-sea coupling are developed. To mimic the main differences
between the fast- atmosphere and the slow-ocean, suitable
multi-space and multi-time scaling are applied, yielding a
balanced synoptic/intraseasonal/interannual-El Niņo regime. In
this limit, the synoptic scale is the fastest atmospheric scale,
the intraseasonal is the intermediate air-sea coupling scale and
El Niņo refers to the slowest interannual ocean scale. The model
equations reveal that the slow wave amplitude evolution depends on
both types of nonlinearities. The wind stress parameterization
allows synoptic scale atmospheric waves to force intraseasonal
variability in the ocean. The intraseasonal ocean temperature
anomaly coupled with the atmosphere through evaporation is able to
force higher order atmospheric variability, whereas
wave-convection coupling provides another source for higher order
atmospheric variability. Nonlinear interactions of intraseasonal
ocean perturbations can also force interannual oceanic
variability. Analytical solutions of the reduced model equations
for a discrete resonant triad interacting through the
atmosphere-ocean fluxes illustrate the model potential to connect
synoptic, intraseasonal, interannual and decadal/multi-decadal
time-scales in the coupled system. We have also analyzed the role
of periodic forcing induced by the sun energy output variability
in the decadal and longer timescales. The presence of periodic
forcing leads to larger amplitude effects at the longer
time-scales. In the fast portion of the time scales, we are
exploring possible resonating triads in non-hydrostatic models
with potential applications in the organization of mesoscale
systems.",
conference-location = "Portland, OR",
conference-year = "26-30 June",
language = "en",
urlaccessdate = "28 abr. 2024"
}