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Steven Dobbie, PhD

Lecturer in Atmospheric Science

Tel: +44 (0) 113-233-6725
Fax: +44 (0) 113-233-6716
Email:

Overview of research interests:

I began my research career focusing on the way in which cloud

and aerosol properties and distributions affect sunlight and hence

climate. More recently, I have focused on the way in which

sunlight affects the evolution of clouds. Both research lines

pervade my current work.

Cirrus cloud modelling: I have established a very strong research interest in cirrus clouds including both mid-latitude and tropical anvil outflows. Inter-comparisons of cirrus models show that there is huge variability in predictions from different models. My group’s work and my involvement in the GCSS inter-comparison are directed toward resolving this. I have projects that focus on the following areas. Understanding the effects of aerosols such as mineral dust on the evolution of tropical anvils to background cirrus using Crystal-Face observations. Modelling of various mid-latitude cirrus clouds are underway which focus on shear effects on these clouds, radiative property sensitivities, and sensitivity of cloud evolution to improvements in the microphysical evolution. We have taken steps to embed these simulations as much as possible in observations, e.g. FIREII, EMERALD, and CHILBOLTON. This has been achieved by initiating models with observations and simulating observing equipment such as radar and lidar within our model. To complement the modelling work, we are developing an ice nucleation chamber to better understand the key ice nucleation properties of various aerosol types and mixtures from different parts of the world (Morocco, India, Spain).

Clouds and radiation: In conjuction with the Canadian Centre for Climate Modelling and Analysis, we have developed a new radiation scheme to account for cloud overlap and within cloud inhomogeneity. This scheme is suitable for implementation in climate models and has been installed in GCM-IV (CCCma). In other work, a 3D radiative transfer model that accounts for the interaction of sunlight with clouds has been installed interactively in the LEM atmospheric model. Work has begun on assessing the 3D radiative effects on cloud evolution for both cirrus and deep convective clouds.

Aerosols and radiation: We have extended the UK Met O LEM atmospheric model to be a fully bin resolved cloud model for warm cloud processes. Into the radiation scheme within this model we have included the absorbing effects of soot. With this new model, we are studying the regional climate impact of soot aerosols on the radiation budget through its influence on cloud properties (semi-direct and indirect effects). In conjunction with the Met Office, a new parameterization of the indirect effect accounting for multi-component aerosols has been developed (Ghosh, Smith). We have assessed the sensitivity of indirect radiative forcing to the multi-component scheme for aerosols combinations such as sea-salt, sulphate, and biomass smoke. The direct radiative properties of aerosols, including the effects of growth with relative humidity, have been parameterised and used to assess global climate forcing in association with CCCma.

Specific research interests:

  • Cirrus model studies – radiative, dynamical, and microphysical interactions. See links to works by Marsham and Dobbie, and Marsham et al.
  • Development of a new diffusivity parameterization for water vapour at low temperatures.
  • Radiative transfer through inhomogeneous cirrus clouds. Part of a NERC Clouds, Water Vapour, and Climate funded project. An article in this area is available if you click here. Have a look at a movie of a simulated cirrus cloud evolving in time, click.
  • The parameterisation of cloud overlap and inhomogeneity for use in climate models. For a preprint of this work click here.
  • Improvement of the water vapour diffusional growth rates for cirrus models. Cloud modelling examples are based on observations from Chilbolton and EMERALD 1.
  • Evaluation of the effects of shear on cirrus layer using Chilbolton observations. Application of results to large scale models. This research is NERC funded through a New Investigator grant.
  • The interplay between dynamical, radiative, and microphysical influences on cloud stability and structure.
  • The effect of 3D radiation on the evolution of cirrus clouds using a coupled MC and LEM model.
  • The modelling of the growth and optical properties of aerosols, such as sulphates and sea salt, for inclusion in GCMs. Inclusion of multicomponent aerosol effects on indirect forcing calculations.
  • The study of the semi-direct effect on climate using a bin resolved LEM model.
  • Modelling of tropical anvil outflow over Florida using Crystal-Face observations.
  • Cloud chamber investigations into properties of ice crystals
  • SWIFT Stratospheric Wind Inteferometer For Transport Studies. Emission line selection for the SWIFT instrument. For more information on the instrument, see and a paper.
  • GCSS working group on cirrus clouds. I am chairman of the GCSS working group on cirrus clouds. This is an international group of cirrus modelers that have the common interest of assessing and improving our cirrus cloud models through common studies. You can visit a page regarding this research at WGC and take part in the latest inter-comparison at the page: WG2 Inter-comparison March 9, 2000

Research Opportunities:

Dr. Dobbie encourages applicants wishing to pursue an MSc or PhD in the following general areas. Radiative, dynamical, and microphysical interactions in cirrus clouds, assessing the representation of cirrus clouds in cloud and GCM models, coupling of 3D Monte Carlo radiation routines with cloud resolving model for cirrus cloud simulations, specification of cloud overlap in GCMs and its implications for climate forcing, parameterizations of the growth and optical properties of aerosols and their effect on the radiation balance.

There are a limited number of NERC-funded M.Res degree opportunities in "Physics of the Earth and Atmosphere" programme offered by the School of the Environment. 50% of the one year degree programme will be devoted to research which is guided by an academic staff member and in collaboration with an external organisation (e.g. UK Met. Office). Contact Dr. Dobbie regarding potential topic selection and criteria for funding.

Past Research Grants:

NERC New Investigators research grant: The effects of shear on the structure of cirrus.

NERC CWVC thematic research grant: Radiative effects of inhomogeneous cirrus clouds.

Research Group:

Research postgraduates:

Mr Gourihar Kulkarni, PhD Student

Gourihar Kulkarni is a PhD postgraduate research student. He has developed and tested a new ice nucleation chamber. He is studying the critical super-saturation and other characteristics of ice nucleation for dust collected from Africa and Spain.

Ms Clare Allen, NERC PhD Student

Clare Allen is a postgraduate research student (NERC quota student). She is studying the effects of multi-dimensional radiation on the evolution of tropical deep convective clouds. This work is based on the Crystal Face observations involving five aircraft, satellites, and ARM ground stations. She is focusing on the way in which multi-dimensional radiation affects the initial development of the cloud and mix phase processes.

Mr Huiyi Yang, PhD Student

Huiyi Yang is a PhD student who is studying the sub-grid vertical transport of ice and moisture in cirrus clouds. His work involves establishing the GCSS WG2 case study and investigating the accuracy and role that sub-grid vertical transport plays in cirrus clouds. He has established an idealized case study based on the ARM SGP IOP of March 9, 2000. The cloud is formed due to gravity waves established by the SW jet flowing over the Rockies. The inter-comparison study was launched in Feb 2007 with first results expected in June 2007. Huiyi’s work investigates the dependence of cirrus on the 1D and 2D comparisons in the LEM and with comparisons to the UM in 1D.

Mr Dan Tang, NERC PhD Student

Dan is addressing the role of parameterizations in GCMs. He is seeking to develop a formalism and code that will analyse cloud models that are imbedded in GCMs and will generate a new code that will collapse inefficiencies in the model and illustrate relationships between prognostic variables in time.

Past Group Members:

Research Fellows:

Dr John Marsham was a NERC funded postdoctoral researcher addressing the effects of shear on the evolution of cirrus clouds. Our aims were two-fold with this work. In addition to studying the effects of shear on cirrus, we have sought to entrench our study in observations. Both of these aspects of cirrus modelling have been largely neglected in past studies. We chose to base our modelling study on an observational case from the Chilbolton site that has been well analysed by the observational work of Robin Hogan (Reading). From the results, we have been able to establish the impact of varying degrees of shear on this modelled and observed case. We have found such things as shear diminishes the embedded convection in the layer and the top of the shear layer has an important influence on the upper level ice water contents. We have modified the original case so as to incite Kelvin-Helmholtz wave breaking in the layer and assessed its impact. Our work has also shown that in the absence of atmospheric lifting, that we can form cloud by breaking gravity waves where no cloud would have otherwise formed. On a practical side, we have adapted the LEM to simulate Chilbolton-type radar observations in the simulations, which allows for much more realistic Fourier analysis and PDF comparisons with cloud ice. Our work also explored comparisons utilising the Chilbolton Doppler radar in order to assess fall velocities in the LEM as compared with observations. In this work, we have assessed the influences of shear on ice and total water distributions (PDFs) and overlap de-correlations, an important link to climate model simulations.

Dr Sat Ghosh, Research Fellow

Dr Sat Ghosh, a NERC funded postdoctoral researcher, is studying the radiative properties of inhomogeneous cirrus clouds. He has run various cirrus modelling cases based in observations. He has explored the microphysical mechanisms at work in cirrus over Adelaide, Australia based on the results from the EMERALD 1 campaign. During this investigation, he has updated aspects of the microphysical treatment and is now exploring the effect of crystal habit on the radiative heating within cloud and its effect on cloud evolution. This work is in collaboration with Prof Peter Jonas and Prof Tom Choularton at UMIST.

Graduated Research postgraduates:

Mr Adrian Hill, NERC PhD Student

Adrian Hill is a second year postgraduate research student (NERC quota student). He is pursuing the coupling between the semi-direct and indirect effects of warm phase clouds. To-date, he has installed a bin resolved cloud microphysical model (the Hebrew microphysical model, including a bin representation of aerosols) in the UK LEM and done validation testing on the model. In addition, he has added a representation of BC in the radiative properties and is beginning to look at the response of the cloud layer to the additional heating.

Mr Jamie Clayton, NERC MRes Student

Jamie used EMERALD observations of ice crystals in the LEM with optical properties that treated the shapes as not only hexagonal shapes (Fu-Liou code) but also other shapes such as aggregates. He determined the error in the cloud evolution and radiative properties as compared to commonly assumed shapes and vertical profiles. .

Mr Dan Tang, NERC MRes Student

Dan was an MRes student. He studied the effect of injection in the UM and determined how much error the UM introduced by requiring a certain distribution in the prognostic scheme.

Modules Taught:

Computer Systems and Programming, ENVI 2240 CCFD 5130& lectures for EARS1160

Advanced Mathematics for Environmental Scientists, ENVI 1310

Advanced Mathematics for Scientists, ENVI 2430

Other Teaching Activities:

- Tutor, Learning and Communications Skills ENVI 1440

- Module leader, Intermediate Mathematics for Environmental Scientists ENVI1300

- Supervisor, Environmental Research ProjectENVI 3030

Other modules previously taught:

Mathematics for Environmental Scientists 2, ENVI 0310

Climate Change: Scientific Issue ENVI 2150

Tutor, Principles and Practices ENVI 2230

Publications:

To view my publications list, click publications

Roles:

- Coordinator for the UG Environment Year Abroad Scheme

- MEnv four year integrated UG programme development

- Deputy Director of the Institute for Atmospheric Science (IAS)

- Head of Mathematics for Environment

Contact Details:

Dr. Steven Dobbie, Lecturer Institute for Atmospheric Science, School of the Environment, University of Leeds, Leeds, UK LS2 9JT.

Tel: +44 (0) 113-233-6725
Fax: +44 (0) 113-233-6716

Email: