Quantifying the spatial and temporal response of UTH and OLR to deep convection over Tropical Africa
File(s)
Author(s)
Ingram, James
Type
Thesis
Abstract
Upper Tropospheric Humidity (UTH) has a strong control on clear-sky Outgoing Longwave Radiation (OLR).
Moisture from the boundary layer is transported to the drier upper troposphere by convective ascent in the
tropics and realised in the form of deep convective clouds. The spatial and temporal response of UTH
and the corresponding OLR are cause for debate. This study uses geostationary satellite imagery from the
Spinning Enhanced Visible and InfraRed Imager (SEVIRI) to estimate UTH using water vapour channel
radiances. Deep convection over Tropical Africa is detected using the difference between 6.2 mm and 7.3
mm brightness temperatures. The sensitivity of TOA brightness temperatures to cloud properties including
cloud top height and optical depth are modelled using the Santa Barbara Disort Atmospheric Radiative
Transfer model with thresholds developed using colocated matchups with CloudSat and CALIPSO cloud
classifications. The most appropriate thresholds are determined using probability statistics and receiver
operating characteristic curves. Deep convective clouds are tracked over their lifetime in June and December
2010 using a cloud tracking algorithm, based on an area overlap method. A general robust pattern in the
UTH response emerges. A stronger response of UTH is found in the spatial domain than that over the
temporal domain. UTH decreases with distance from the cloud edge, whilst a small increase is seen over
the cloud lifetime. This was found to be controlled by cloud size and cloud lifetime, with larger and longer
lived clouds causing a stronger perturbation in UTH. The UTH response was found to be stronger in June
than in December. A strong negative correlation is found between UTH and OLR perturbations, with OLR
measured using the Geostationary Earth Radiation Budget (GERB) instrument. This pattern is stronger in
December than June.
Moisture from the boundary layer is transported to the drier upper troposphere by convective ascent in the
tropics and realised in the form of deep convective clouds. The spatial and temporal response of UTH
and the corresponding OLR are cause for debate. This study uses geostationary satellite imagery from the
Spinning Enhanced Visible and InfraRed Imager (SEVIRI) to estimate UTH using water vapour channel
radiances. Deep convection over Tropical Africa is detected using the difference between 6.2 mm and 7.3
mm brightness temperatures. The sensitivity of TOA brightness temperatures to cloud properties including
cloud top height and optical depth are modelled using the Santa Barbara Disort Atmospheric Radiative
Transfer model with thresholds developed using colocated matchups with CloudSat and CALIPSO cloud
classifications. The most appropriate thresholds are determined using probability statistics and receiver
operating characteristic curves. Deep convective clouds are tracked over their lifetime in June and December
2010 using a cloud tracking algorithm, based on an area overlap method. A general robust pattern in the
UTH response emerges. A stronger response of UTH is found in the spatial domain than that over the
temporal domain. UTH decreases with distance from the cloud edge, whilst a small increase is seen over
the cloud lifetime. This was found to be controlled by cloud size and cloud lifetime, with larger and longer
lived clouds causing a stronger perturbation in UTH. The UTH response was found to be stronger in June
than in December. A strong negative correlation is found between UTH and OLR perturbations, with OLR
measured using the Geostationary Earth Radiation Budget (GERB) instrument. This pattern is stronger in
December than June.
Version
Open Access
Date Issued
2015-09
Date Awarded
2016-01
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Brindley, Helen
Czaja, Arnaud
Sponsor
Natural Environment Research Council (Great Britain)
Grant Number
NE/J500094/1
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)