DATE:
TIME:
LOCATION:
SPEAKER:
TITLE:
Tuesday, 24 March 2015
11 a.m.
Mesa Lab, Main Seminar Room
NCAR, 1850 Table Mesa Drive
Juliana Dias, NOAA ESRL/CIRES
Synoptic scale interactions between
extratropical waves and rainfall in
the Eastern Pacific ITCZ
ABSTRACT:
Coupling between moist convective processes and large-scale circulation is at the core of
tropical-extratropical atmospheric interactions, which, in turn, are known to strongly modulate
rainfall at low latitudes. For example, within the tropical Eastern Pacific, observations suggest
that poleward transport of moisture and energy is particularly dependent upon intrusion of
large-scale transient Rossby waves from the extratropics towards the equator, particularly
during northern winter. Theories for the relationship between low latitude moist convection
and extratropical waves have emphasized the role of upper level potential vorticity (PV)
intrusions associated with Rossby wave breaking. In this talk, two major drawbacks of this
approach are discussed: the limitations of PV inversion at low latitudes and the neglect of
latent heating feedbacks. To address these limitations, an alternative reduced model is
proposed that is based on a barotropic-baroclinic shallow water system coupled to a water
vapor equation. The water vapor equation is coupled to the dynamical variables through a
simple parametrization for precipitation, allowing for a two-way feedback between
precipitation and waves. This model is used to investigate modulations of equatorial rainfall,
in particular, the relative roles of zonal moisture transport by tropical waves and meridional
moisture advection by extratropical waves. By integrating the model using initial conditions
consistent with the northern winter basic state, we demonstrate the key role of advection of
moisture towards the equator due to barotropic Rossby waves. The transient response and
tropical rainfall sensitivity to the precipitation parametrization and barotropic wave forcing are
discussed, as well as the model overall agreement with observations.
Seminars are live webcast: http://www.fin.ucar.edu/it/mms/ml-live.htm
For more information, contact Gaylynn Potemkin, email potemkin@ucar.edu, phone: 303.497.1618