The Dynamics of the Venusian Mesosphere and Thermosphere
Author(s)
Tingle, Susannah
Type
Thesis
Abstract
We present the first circulation model of Venus' atmosphere to couple the
super-rotating cloud tops and upper thermosphere. To drive these simulations,
we formulate the first continuous semi-empirical model of atmospheric
structure between 60-250 km. Our model hydrostatically links the VIRA and
VTS3 models. Our approach is validated by comparisons with observations
where we find a good agreement with data.
We base our dynamic model on the Müller-Wodarg et al. [2003] general
circulation model (GCM) of Titan's thermosphere. Our simulations solve
the full non-linear Navier-Stokes momentum equation assuming a realistic
thermal structure and lower boundary super-rotation. We find our derived
winds are consistent with much of the data between 70-120 km.
Solving the full momentum equation we find dynamics below 80km are
predominately cyclostrophic. Near 75km we find a good agreement between
our GCM, cyclostrophic and cloud tracked winds between 45-85⁰ latitude.
Equatorward of 30⁰ cyclostrophic winds decrease steeply with latitude. This
is not seen in our GCM winds, which are sustained by an equatorward transport
of momentum, neglected in the cyclostrophic approximation. Above
80km we find a balance of advection and pressure gradients replaces cyclostrophic
balance poleward of (50-60⁰).
Above 75km a pole-to-equator temperature gradient drives equatorward
winds with peak speeds of 100ms⁻1 near 95 km, and zonal winds decrease
with height. Zonal forcing above 90km drives a reversal in dayside meridional
winds and accelerates a subsolar-to-antisolar
flow. We find the winds between
90-150km are not characterised by a simple balance of accelerations.
Above 150km we find a symmetric subsolar-to-antisolar
flow, characterised
by a balance of horizontal pressure gradients and viscosity with 200 ms⁻1
cross terminator winds. Our simulations address the origin of the thermospheric
super-rotation. We find the cloud top super-rotation does not propagate
above 100 km, nor is a super-rotation above 150km driven in situ by
our pressure gradients.
super-rotating cloud tops and upper thermosphere. To drive these simulations,
we formulate the first continuous semi-empirical model of atmospheric
structure between 60-250 km. Our model hydrostatically links the VIRA and
VTS3 models. Our approach is validated by comparisons with observations
where we find a good agreement with data.
We base our dynamic model on the Müller-Wodarg et al. [2003] general
circulation model (GCM) of Titan's thermosphere. Our simulations solve
the full non-linear Navier-Stokes momentum equation assuming a realistic
thermal structure and lower boundary super-rotation. We find our derived
winds are consistent with much of the data between 70-120 km.
Solving the full momentum equation we find dynamics below 80km are
predominately cyclostrophic. Near 75km we find a good agreement between
our GCM, cyclostrophic and cloud tracked winds between 45-85⁰ latitude.
Equatorward of 30⁰ cyclostrophic winds decrease steeply with latitude. This
is not seen in our GCM winds, which are sustained by an equatorward transport
of momentum, neglected in the cyclostrophic approximation. Above
80km we find a balance of advection and pressure gradients replaces cyclostrophic
balance poleward of (50-60⁰).
Above 75km a pole-to-equator temperature gradient drives equatorward
winds with peak speeds of 100ms⁻1 near 95 km, and zonal winds decrease
with height. Zonal forcing above 90km drives a reversal in dayside meridional
winds and accelerates a subsolar-to-antisolar
flow. We find the winds between
90-150km are not characterised by a simple balance of accelerations.
Above 150km we find a symmetric subsolar-to-antisolar
flow, characterised
by a balance of horizontal pressure gradients and viscosity with 200 ms⁻1
cross terminator winds. Our simulations address the origin of the thermospheric
super-rotation. We find the cloud top super-rotation does not propagate
above 100 km, nor is a super-rotation above 150km driven in situ by
our pressure gradients.
Date Issued
2011-10
Date Awarded
2011-11
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Müller-Wodarg, Ingo
Sponsor
Science and Technology Facilities Council
Creator
Tingle, Susannah
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)