Stratosphere-Troposphere Coupling and Oceanic Feedbacks in an Aquaplanet Model
File(s)
Author(s)
Trencham, Natasha Elise
Type
Thesis
Abstract
Since the 90’s, there have been many studies looking at the impact of stratospheric temperature perturbations (STP’s) on the troposphere below, and the mechanisms involved. However, it is
not well-understood how these interactions might be modified by atmosphere-ocean coupling.
This holds particular relevance to the study of e.g. ozone depletion/recovery in the Southern
Ocean region.
To investigate this, abrupt uniform, polar, and equatorial STP’s – corresponding to different
types of forcings - were applied to the atmosphere of MITgcm in an aquaplanet, double-drake configuration. Each was conducted in three different versions of the model: atmosphere-only, atmosphere + slab-ocean, and fully-coupled atmosphere + ocean. In the atmosphere-only model, atmospheric responses similar to those of previous studies were recorded, underscoring their generic nature. In the coupled models, an initial weakening (~decades), and – in the fully coupled model - subsequent strengthening and poleward-shift (~centuries) of the underlying
atmospheric response was produced, in polar/equatorial heating experiments. Uniform heating saw the latter process occur initially too. Sea surface temperature (SST) anomalies were found to drive these changes, with extratropical/tropical anomalies controlling the former/latter process.
These were in turn attributable to changes in the zonal winds, causing anomalies in the turbulent
and ocean heat fluxes, although uniform STP’s saw SST changes that were more controlled by
large, near-uniform anomalous downwelling longwave fluxes.
Our results highlight the importance of incorporating atmosphere-ocean coupling when
studying the effects of STP’s, especially over longer timescales (&100 years). With respect
to ozone depletion in the Southern Ocean, they suggest an amplified poleward jet shift which
- as greenhouse gases continue to rise – may continue and amplify further into the 21st/22nd
century.
not well-understood how these interactions might be modified by atmosphere-ocean coupling.
This holds particular relevance to the study of e.g. ozone depletion/recovery in the Southern
Ocean region.
To investigate this, abrupt uniform, polar, and equatorial STP’s – corresponding to different
types of forcings - were applied to the atmosphere of MITgcm in an aquaplanet, double-drake configuration. Each was conducted in three different versions of the model: atmosphere-only, atmosphere + slab-ocean, and fully-coupled atmosphere + ocean. In the atmosphere-only model, atmospheric responses similar to those of previous studies were recorded, underscoring their generic nature. In the coupled models, an initial weakening (~decades), and – in the fully coupled model - subsequent strengthening and poleward-shift (~centuries) of the underlying
atmospheric response was produced, in polar/equatorial heating experiments. Uniform heating saw the latter process occur initially too. Sea surface temperature (SST) anomalies were found to drive these changes, with extratropical/tropical anomalies controlling the former/latter process.
These were in turn attributable to changes in the zonal winds, causing anomalies in the turbulent
and ocean heat fluxes, although uniform STP’s saw SST changes that were more controlled by
large, near-uniform anomalous downwelling longwave fluxes.
Our results highlight the importance of incorporating atmosphere-ocean coupling when
studying the effects of STP’s, especially over longer timescales (&100 years). With respect
to ozone depletion in the Southern Ocean, they suggest an amplified poleward jet shift which
- as greenhouse gases continue to rise – may continue and amplify further into the 21st/22nd
century.
Version
Open Access
Date Issued
2021-06
Date Awarded
2022-03
Copyright Statement
Creative Commons Attribution-Non Commercial 4.0 International Licence
License URL
Advisor
Czaja, Arnaud
Haigh, Joanna
Sponsor
Natural Environment Research Council (Great Britain)
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)