The β-effect in tropical cyclones: impact on intensity and sensitivity to temperature
File(s)
Author(s)
Corsaro, Carlo Maria
Type
Thesis
Abstract
Tropical cyclones are large weather systems whose development is characterised by
complex physical processes that are not yet fully understood. A better understanding
of how cyclones work is vital to help forecasters make more accurate predictions. The
objective of this study is to contribute to the understanding of the track and intensity
evolution in relation to the β-effect.
While the β-effect has been widely studied, its response to changes in environmental
conditions has been investigated only marginally. To this end a series of idealised
experiments using the Weather Research and Forecasting model is performed. The
sensitivity of the β-drift is investigated with no background flow by changing uniformly
sea surface and atmospheric temperature. With increasing temperature tropical
cyclones become more intense, larger and move faster with a stronger westward
deflection. In particular, there is a linear relationship between the β-drift speed and
size above a gale-force wind radius of 250 km.
Another aspect investigated is the impact of the β-effect on cyclone intensity. A
comparison between an experiment with variable Coriolis parameter f and one on an
f -plane shows that after the initial intensification the former has a lower intensity and
undergoes a weakening not present in the latter. The main reason behind this weakening
is the dry intrusion of a mid-upper tropospheric westerly flow. Back-trajectories show
that the intrusion originates from the anticyclonic recirculation of the air expelled from the cyclone deep convection at earlier times, eventually causing a self-weakening of the
cyclone.
A real-case simulation of Hurricane Katrina (2005) and two sensitivity experiments
are performed to investigate the results of the idealised simulations. The occurrence of
both the β-drift sensitivity to temperature and the dry intrusion further demonstrates
that the results presented here might contribute to the general understanding of the
intensity and track evolution of tropical cyclones.
complex physical processes that are not yet fully understood. A better understanding
of how cyclones work is vital to help forecasters make more accurate predictions. The
objective of this study is to contribute to the understanding of the track and intensity
evolution in relation to the β-effect.
While the β-effect has been widely studied, its response to changes in environmental
conditions has been investigated only marginally. To this end a series of idealised
experiments using the Weather Research and Forecasting model is performed. The
sensitivity of the β-drift is investigated with no background flow by changing uniformly
sea surface and atmospheric temperature. With increasing temperature tropical
cyclones become more intense, larger and move faster with a stronger westward
deflection. In particular, there is a linear relationship between the β-drift speed and
size above a gale-force wind radius of 250 km.
Another aspect investigated is the impact of the β-effect on cyclone intensity. A
comparison between an experiment with variable Coriolis parameter f and one on an
f -plane shows that after the initial intensification the former has a lower intensity and
undergoes a weakening not present in the latter. The main reason behind this weakening
is the dry intrusion of a mid-upper tropospheric westerly flow. Back-trajectories show
that the intrusion originates from the anticyclonic recirculation of the air expelled from the cyclone deep convection at earlier times, eventually causing a self-weakening of the
cyclone.
A real-case simulation of Hurricane Katrina (2005) and two sensitivity experiments
are performed to investigate the results of the idealised simulations. The occurrence of
both the β-drift sensitivity to temperature and the dry intrusion further demonstrates
that the results presented here might contribute to the general understanding of the
intensity and track evolution of tropical cyclones.
Version
Open Access
Date Issued
2017-01
Date Awarded
2017-07
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Toumi, Ralf
Sponsor
European Union
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)