T. Choularton - Profile on Academia.edu (original) (raw)
Papers by T. Choularton
?'A comparison of in-situ Arctic and Antarctic cloud microphysics measurements
In Daca Atmosphere and Cryosphere Assembly 08 Jul 2013 13 Jul 2013 Davos Switzerland 2013, Jul 9, 2013
• Quantification of factors influencing cloud responses to warming across the full range of relev... more • Quantification of factors influencing cloud responses to warming across the full range of relevant scales. • First measurements linking clouds and warm-rain processes to meso and sub-mesoscale motions in the lower atmosphere and upper ocean. • Novel application of remote sensing, isotopologue measurements, and un-crewed vehicles (to study the remote marine environment.
Modelling and Measurements ofNO X, Ozone and Hydrocarbons to Fruit Orchards and Gorse Heaths
The purpose of this document is to describe the data processing methods used in the main article ... more The purpose of this document is to describe the data processing methods used in the main article and the criteria that were employed to derive a given solution set. The procedure followed is similar to that of Allan et al. (2010), in that the number of factors were first constrained, followed by the correct value of 'fpeak'. The PMF Evaluation Toolkit (Ulbrich et al., 2009) was used, employing version 4.2 of the PMF2 executable (Paatero, 1997).
Observation of microphysics and dynamics of an active cold front
Modelling studies of cirrus wave clouds using an explicit microphysics model
Air-Surface Exchange of Gases and Particles (2000), 2001
Weekly collections of samples of precipitation and hill cloud water have been made at Holme Moss ... more Weekly collections of samples of precipitation and hill cloud water have been made at Holme Moss (530 m.a.s.l.) in the southern Pennines covering a six-year period (1994-1999). In addition continuous meteorological measurements have been conducted at the site for a five year period (1995-1999). The concentrations of major ions in the samples have been determined by ion chromatography. Analysis of ion concentrations as a function of wind direction reveals that the ions with anthropogenic sources (SO −− 4 , NO − 3 , NH + 4 , H +) exhibit higher concentrations during easterly wind directions whilst the ions with predominantly marine origins (Na + , Cl − , Ca ++ , Mg ++ , K +) have concentrations that are not significantly dependant on wind direction. Precipitation and cloud deposition are strongly correlated to south-westerly wind directions with a secondary peak occurring for north-easterly directions. Fifty nine per cent of ion deposition by rain was found to occur during wind from the SSW to W sector. The average concentrations of ions in cloud water were found to be much higher than those in rain (by factors of between 2.5 and 4.2). It is thought that the high precipitation and annual deposition of ions by precipitation at Holme Moss is due in part to the enrichment of ion concentrations in precipitation by the scavenging of more concentrated cap cloud droplets (the 'seeder-feeder effect'). Comparison with data from a nearby lower level site shows encouraging agreement with the scheme currently used in the U.K. deposition mapping procedure to incorporate the influence of orography on deposition by precipitation.
Constraining calculations of latent heat release in simulations of extratropical weather using in-situ microphysics data
Atmospheric Chemistry and Physics, 2018
Large-eddy simulations are performed to investigate the influence of cloud microphysics on the ev... more Large-eddy simulations are performed to investigate the influence of cloud microphysics on the evolution of low-level clouds that form over southern West Africa during the monsoon season. We find that, even in clouds that are not precipitating, the size of cloud droplets has a non-negligible effect on liquid water path. This is explained through the effects of droplet sedimentation, which acts to remove liquid water from the entrainment zone close to cloud top, increasing the liquid water path. Sedimentation also produces a more heterogeneous cloud structure and lowers cloud base height. Our results imply that an appropriate parameterization of the effects of sedimentation is required to improve the representation of the diurnal cycle of the atmospheric boundary layer over southern West Africa in large-scale models.
Atmospheric Chemistry and Physics Discussions, 2018
Mineral dust is an important component of the climate system, affecting the radiation balance, cl... more Mineral dust is an important component of the climate system, affecting the radiation balance, cloud properties, biogeochemical cycles, regional circulation and precipitation, as well as having negative effects on aviation, solar energy generation and human health. Dust size and composition has an impact on all these processes. However, changes in dust size distribution and composition during transport, particularly for coarse particles, are poorly understood and poorly represented in climate models. Here we present new in-situ airborne observations of dust in the Saharan Air Layer (SAL) and the Marine Boundary Layer (MBL) during the beginning of its trans-Atlantic transport pathway, from the AER-D fieldwork in August 2015, within the peak season of North African dust export. This study focuses on coarse mode dust properties, including size distribution, mass loading, shape, composition, refractive indices and optical properties. Size distributions from 0.1 to 100 µm diameter (d) are presented, fully incorporating the coarse and giant modes of dust. Within the SAL, particles larger than 20 µm diameter were always present up to 5km altitude, in concentrations over 10 -5 cm -3 , constituting up to 40% of dust mass. Mean effective diameter and volume median diameter were 4.0 µm and 5.5 µm respectively. Larger particles were detected in the SAL than can be explained by sedimentation theory alone. Coarse mode composition was dominated by quartz and alumino-silicates; the accumulation mode showed a strong contribution from sulfate-rich and sea salt particles. In the SAL, measured single scattering albedos (SSAs) at 550nm representing d<2.5 µm were 0.93 to 0.98 (mean 0.97). Optical properties calculated for the full size distribution (0.1<d<100 µm) resulted in lower SSAs of 0.91-0.98 (mean 0.95) and mass extinction
Comparison of cloud properties between cloudsat retrievals and airplane measurements in mixed-phase cloud layers of weak convective and stratus clouds
Advances in Atmospheric Sciences, 2015
Cloud microphysical properties including liquid and ice particle number concentration (NC), liqui... more Cloud microphysical properties including liquid and ice particle number concentration (NC), liquid water content (LWC), ice water content (IWC) and effective radius (RE) were retrieved from CloudSat data for a weakly convective and a widespread stratus cloud. Within the mixed-phase cloud layers, liquid-phase fractions needed to be assumed in the data retrieval process, and one existing linear (p1) and two exponential (p2 and p3) functions, which estimate the liquid-phase fraction as a function of subfreezing temperature (from −20°C to 0°C), were tested. The retrieved NC, LWC, IWC and RE using p1 were on average larger than airplane measurements in the same cloud layer. Function p2 performed better than p1 or p3 in retrieving the NCs of cloud droplets in the convective cloud, while function p1 performed better in the stratus cloud. Function p3 performed better in LWC estimation in both convective and stratus clouds. The REs of cloud droplets calculated using the retrieved cloud droplet NC and LWC were closer to the values of in situ observations than those retrieved directly using the p1 function. The retrieved NCs of ice particles in both convective and stratus clouds, on the assumption of liquid-phase fraction during the retrieval of liquid droplet NCs, were closer to those of airplane observations than on the assumption of function p1.
Journal of Atmospheric Chemistry, 1994
An overview is given of the Kleiner Feldberg cloud experiment performed from 27 October until 13 ... more An overview is given of the Kleiner Feldberg cloud experiment performed from 27 October until 13 November 1990. The experiment was carried out by numerous European research groups as a joint effort within the EUROTRAC-GCE project in order to study the interaction of cloud droplets with atmospheric trace constituents. After a description of the observational site and the
Microphysical properties of frontal clouds
Journal of Applied Meteorology and Climatology, 2017
During the Cloud and Aerosol Characterization Experiment (CLACE) 2013 field campaign at the High ... more During the Cloud and Aerosol Characterization Experiment (CLACE) 2013 field campaign at the High Altitude Research Station Jungfraujoch, Switzerland, optically thin pure ice clouds and ice crystal precipitation were measured using holographic and other in situ particle instruments. For cloud particles, particle images, positions in space, concentrations, and size distributions were obtained, allowing one to extract size distributions classified by ice crystal habit. Small ice crystals occurring under conditions with a vertically thin cloud layer above and a stratocumulus layer approximately 1 km below exhibit similar properties in size and crystal habits as Antarctic/Arctic diamond dust. Also, ice crystal precipitation stemming from midlevel clouds subsequent to the diamond dust event was observed with a larger fraction of ice crystal aggregates when compared with the diamond dust. In another event, particle size distributions could be derived from mostly irregular ice crystals and ...
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2008
An assessment is made herein of the proposal that controlled global cooling sufficient to balance... more An assessment is made herein of the proposal that controlled global cooling sufficient to balance global warming resulting from increasing atmospheric CO 2 concentrations might be achieved by seeding low-level, extensive maritime clouds with seawater particles that act as cloud condensation nuclei, thereby activating new droplets and increasing cloud albedo (and possibly longevity). This paper focuses on scientific and meteorological aspects of the scheme. Associated technological issues are addressed in a companion paper. Analytical calculations, cloud modelling and (particularly) GCM computations suggest that, if outstanding questions are satisfactorily resolved, the controllable, globally averaged negative forcing resulting from deployment of this scheme might be sufficient to balance the positive forcing associated with a doubling of CO 2 concentration. This statement is supported quantitatively by recent observational evidence from three disparate sources. We conclude that this...
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2012
The idea behind the marine cloud-brightening (MCB) geoengineering technique is that seeding marin... more The idea behind the marine cloud-brightening (MCB) geoengineering technique is that seeding marine stratocumulus clouds with copious quantities of roughly monodisperse sub-micrometre sea water particles might significantly enhance the cloud droplet number concentration, and thereby the cloud albedo and possibly longevity. This would produce a cooling, which general circulation model (GCM) computations suggest could—subject to satisfactory resolution of technical and scientific problems identified herein—have the capacity to balance global warming up to the carbon dioxide-doubling point. We describe herein an account of our recent research on a number of critical issues associated with MCB. This involves (i) GCM studies, which are our primary tools for evaluating globally the effectiveness of MCB, and assessing its climate impacts on rainfall amounts and distribution, and also polar sea-ice cover and thickness; (ii) high-resolution modelling of the effects of seeding on marine strato...
Exploring the impact of ice phase microphysical processes on mesoscale structures in mid-latitude cyclones using WRF Motivation
Journal of Applied Meteorology and Climatology, 2017
During the Cloud and Aerosol Characterization Experiment (CLACE) 2013 field campaign at the High ... more During the Cloud and Aerosol Characterization Experiment (CLACE) 2013 field campaign at the High Altitude Research Station Jungfraujoch, Switzerland, optically thin pure ice clouds and ice crystal precipitation were measured using holographic and other in situ particle instruments. For cloud particles, particle images, positions in space, concentrations, and size distributions were obtained, allowing one to extract size distributions classified by ice crystal habit. Small ice crystals occurring under conditions with a vertically thin cloud layer above and a stratocumulus layer approximately 1 km below exhibit similar properties in size and crystal habits as Antarctic/Arctic diamond dust. Also, ice crystal precipitation stemming from midlevel clouds subsequent to the diamond dust event was observed with a larger fraction of ice crystal aggregates when compared with the diamond dust. In another event, particle size distributions could be derived from mostly irregular ice crystals and ...
?'A comparison of in-situ Arctic and Antarctic cloud microphysics measurements
In Daca Atmosphere and Cryosphere Assembly 08 Jul 2013 13 Jul 2013 Davos Switzerland 2013, Jul 9, 2013
• Quantification of factors influencing cloud responses to warming across the full range of relev... more • Quantification of factors influencing cloud responses to warming across the full range of relevant scales. • First measurements linking clouds and warm-rain processes to meso and sub-mesoscale motions in the lower atmosphere and upper ocean. • Novel application of remote sensing, isotopologue measurements, and un-crewed vehicles (to study the remote marine environment.
Modelling and Measurements ofNO X, Ozone and Hydrocarbons to Fruit Orchards and Gorse Heaths
The purpose of this document is to describe the data processing methods used in the main article ... more The purpose of this document is to describe the data processing methods used in the main article and the criteria that were employed to derive a given solution set. The procedure followed is similar to that of Allan et al. (2010), in that the number of factors were first constrained, followed by the correct value of 'fpeak'. The PMF Evaluation Toolkit (Ulbrich et al., 2009) was used, employing version 4.2 of the PMF2 executable (Paatero, 1997).
Observation of microphysics and dynamics of an active cold front
Modelling studies of cirrus wave clouds using an explicit microphysics model
Air-Surface Exchange of Gases and Particles (2000), 2001
Weekly collections of samples of precipitation and hill cloud water have been made at Holme Moss ... more Weekly collections of samples of precipitation and hill cloud water have been made at Holme Moss (530 m.a.s.l.) in the southern Pennines covering a six-year period (1994-1999). In addition continuous meteorological measurements have been conducted at the site for a five year period (1995-1999). The concentrations of major ions in the samples have been determined by ion chromatography. Analysis of ion concentrations as a function of wind direction reveals that the ions with anthropogenic sources (SO −− 4 , NO − 3 , NH + 4 , H +) exhibit higher concentrations during easterly wind directions whilst the ions with predominantly marine origins (Na + , Cl − , Ca ++ , Mg ++ , K +) have concentrations that are not significantly dependant on wind direction. Precipitation and cloud deposition are strongly correlated to south-westerly wind directions with a secondary peak occurring for north-easterly directions. Fifty nine per cent of ion deposition by rain was found to occur during wind from the SSW to W sector. The average concentrations of ions in cloud water were found to be much higher than those in rain (by factors of between 2.5 and 4.2). It is thought that the high precipitation and annual deposition of ions by precipitation at Holme Moss is due in part to the enrichment of ion concentrations in precipitation by the scavenging of more concentrated cap cloud droplets (the 'seeder-feeder effect'). Comparison with data from a nearby lower level site shows encouraging agreement with the scheme currently used in the U.K. deposition mapping procedure to incorporate the influence of orography on deposition by precipitation.
Constraining calculations of latent heat release in simulations of extratropical weather using in-situ microphysics data
Atmospheric Chemistry and Physics, 2018
Large-eddy simulations are performed to investigate the influence of cloud microphysics on the ev... more Large-eddy simulations are performed to investigate the influence of cloud microphysics on the evolution of low-level clouds that form over southern West Africa during the monsoon season. We find that, even in clouds that are not precipitating, the size of cloud droplets has a non-negligible effect on liquid water path. This is explained through the effects of droplet sedimentation, which acts to remove liquid water from the entrainment zone close to cloud top, increasing the liquid water path. Sedimentation also produces a more heterogeneous cloud structure and lowers cloud base height. Our results imply that an appropriate parameterization of the effects of sedimentation is required to improve the representation of the diurnal cycle of the atmospheric boundary layer over southern West Africa in large-scale models.
Atmospheric Chemistry and Physics Discussions, 2018
Mineral dust is an important component of the climate system, affecting the radiation balance, cl... more Mineral dust is an important component of the climate system, affecting the radiation balance, cloud properties, biogeochemical cycles, regional circulation and precipitation, as well as having negative effects on aviation, solar energy generation and human health. Dust size and composition has an impact on all these processes. However, changes in dust size distribution and composition during transport, particularly for coarse particles, are poorly understood and poorly represented in climate models. Here we present new in-situ airborne observations of dust in the Saharan Air Layer (SAL) and the Marine Boundary Layer (MBL) during the beginning of its trans-Atlantic transport pathway, from the AER-D fieldwork in August 2015, within the peak season of North African dust export. This study focuses on coarse mode dust properties, including size distribution, mass loading, shape, composition, refractive indices and optical properties. Size distributions from 0.1 to 100 µm diameter (d) are presented, fully incorporating the coarse and giant modes of dust. Within the SAL, particles larger than 20 µm diameter were always present up to 5km altitude, in concentrations over 10 -5 cm -3 , constituting up to 40% of dust mass. Mean effective diameter and volume median diameter were 4.0 µm and 5.5 µm respectively. Larger particles were detected in the SAL than can be explained by sedimentation theory alone. Coarse mode composition was dominated by quartz and alumino-silicates; the accumulation mode showed a strong contribution from sulfate-rich and sea salt particles. In the SAL, measured single scattering albedos (SSAs) at 550nm representing d<2.5 µm were 0.93 to 0.98 (mean 0.97). Optical properties calculated for the full size distribution (0.1<d<100 µm) resulted in lower SSAs of 0.91-0.98 (mean 0.95) and mass extinction
Comparison of cloud properties between cloudsat retrievals and airplane measurements in mixed-phase cloud layers of weak convective and stratus clouds
Advances in Atmospheric Sciences, 2015
Cloud microphysical properties including liquid and ice particle number concentration (NC), liqui... more Cloud microphysical properties including liquid and ice particle number concentration (NC), liquid water content (LWC), ice water content (IWC) and effective radius (RE) were retrieved from CloudSat data for a weakly convective and a widespread stratus cloud. Within the mixed-phase cloud layers, liquid-phase fractions needed to be assumed in the data retrieval process, and one existing linear (p1) and two exponential (p2 and p3) functions, which estimate the liquid-phase fraction as a function of subfreezing temperature (from −20°C to 0°C), were tested. The retrieved NC, LWC, IWC and RE using p1 were on average larger than airplane measurements in the same cloud layer. Function p2 performed better than p1 or p3 in retrieving the NCs of cloud droplets in the convective cloud, while function p1 performed better in the stratus cloud. Function p3 performed better in LWC estimation in both convective and stratus clouds. The REs of cloud droplets calculated using the retrieved cloud droplet NC and LWC were closer to the values of in situ observations than those retrieved directly using the p1 function. The retrieved NCs of ice particles in both convective and stratus clouds, on the assumption of liquid-phase fraction during the retrieval of liquid droplet NCs, were closer to those of airplane observations than on the assumption of function p1.
Journal of Atmospheric Chemistry, 1994
An overview is given of the Kleiner Feldberg cloud experiment performed from 27 October until 13 ... more An overview is given of the Kleiner Feldberg cloud experiment performed from 27 October until 13 November 1990. The experiment was carried out by numerous European research groups as a joint effort within the EUROTRAC-GCE project in order to study the interaction of cloud droplets with atmospheric trace constituents. After a description of the observational site and the
Microphysical properties of frontal clouds
Journal of Applied Meteorology and Climatology, 2017
During the Cloud and Aerosol Characterization Experiment (CLACE) 2013 field campaign at the High ... more During the Cloud and Aerosol Characterization Experiment (CLACE) 2013 field campaign at the High Altitude Research Station Jungfraujoch, Switzerland, optically thin pure ice clouds and ice crystal precipitation were measured using holographic and other in situ particle instruments. For cloud particles, particle images, positions in space, concentrations, and size distributions were obtained, allowing one to extract size distributions classified by ice crystal habit. Small ice crystals occurring under conditions with a vertically thin cloud layer above and a stratocumulus layer approximately 1 km below exhibit similar properties in size and crystal habits as Antarctic/Arctic diamond dust. Also, ice crystal precipitation stemming from midlevel clouds subsequent to the diamond dust event was observed with a larger fraction of ice crystal aggregates when compared with the diamond dust. In another event, particle size distributions could be derived from mostly irregular ice crystals and ...
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2008
An assessment is made herein of the proposal that controlled global cooling sufficient to balance... more An assessment is made herein of the proposal that controlled global cooling sufficient to balance global warming resulting from increasing atmospheric CO 2 concentrations might be achieved by seeding low-level, extensive maritime clouds with seawater particles that act as cloud condensation nuclei, thereby activating new droplets and increasing cloud albedo (and possibly longevity). This paper focuses on scientific and meteorological aspects of the scheme. Associated technological issues are addressed in a companion paper. Analytical calculations, cloud modelling and (particularly) GCM computations suggest that, if outstanding questions are satisfactorily resolved, the controllable, globally averaged negative forcing resulting from deployment of this scheme might be sufficient to balance the positive forcing associated with a doubling of CO 2 concentration. This statement is supported quantitatively by recent observational evidence from three disparate sources. We conclude that this...
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2012
The idea behind the marine cloud-brightening (MCB) geoengineering technique is that seeding marin... more The idea behind the marine cloud-brightening (MCB) geoengineering technique is that seeding marine stratocumulus clouds with copious quantities of roughly monodisperse sub-micrometre sea water particles might significantly enhance the cloud droplet number concentration, and thereby the cloud albedo and possibly longevity. This would produce a cooling, which general circulation model (GCM) computations suggest could—subject to satisfactory resolution of technical and scientific problems identified herein—have the capacity to balance global warming up to the carbon dioxide-doubling point. We describe herein an account of our recent research on a number of critical issues associated with MCB. This involves (i) GCM studies, which are our primary tools for evaluating globally the effectiveness of MCB, and assessing its climate impacts on rainfall amounts and distribution, and also polar sea-ice cover and thickness; (ii) high-resolution modelling of the effects of seeding on marine strato...
Exploring the impact of ice phase microphysical processes on mesoscale structures in mid-latitude cyclones using WRF Motivation
Journal of Applied Meteorology and Climatology, 2017
During the Cloud and Aerosol Characterization Experiment (CLACE) 2013 field campaign at the High ... more During the Cloud and Aerosol Characterization Experiment (CLACE) 2013 field campaign at the High Altitude Research Station Jungfraujoch, Switzerland, optically thin pure ice clouds and ice crystal precipitation were measured using holographic and other in situ particle instruments. For cloud particles, particle images, positions in space, concentrations, and size distributions were obtained, allowing one to extract size distributions classified by ice crystal habit. Small ice crystals occurring under conditions with a vertically thin cloud layer above and a stratocumulus layer approximately 1 km below exhibit similar properties in size and crystal habits as Antarctic/Arctic diamond dust. Also, ice crystal precipitation stemming from midlevel clouds subsequent to the diamond dust event was observed with a larger fraction of ice crystal aggregates when compared with the diamond dust. In another event, particle size distributions could be derived from mostly irregular ice crystals and ...