Douglas Parker's Research Page

My research is concerned with the dynamics of different kinds of weather systems. I have worked in Europe and Africa, studying atmospheric fronts, cyclones and cumulonimbus (thunderstorm) systems. Most of my work takes place as a part of the Atmospheric Dynamics Group at the Institute for Atmospheric Science in the School of Earth and Environment of the University of Leeds. I am also a Principal Investigator within the National Centre for Atmospheric Science (NCAS). I have long-standing scientific collaborations with the Met Office and CEH Wallingford.

Current and former research topics:

African Monsoon Multidisciplinary Analysis (AMMA).
AMMA is the largest and most far-reaching experiment into the environment and climate of Africa which has ever been undertaken. To date (Nov 2009) more than 350 papers have been produced from the AMMA programme. I am coordinating the UK contributions to AMMA; in particular I am leading a UK consortium studying the physical and chemical processes occurring between the land and atmosphere. The team at Leeds are focussing on the dynamics of the atmospheric response to surface state (especially soil moisture in the northern Sahel). I have also been closely concerned with the reactivation of the AMMA upper-air observational network (see Parker et al. 2008).

Using aircraft and remote sensing data from the AMMA field campaigns, we have established for the first time in observations that soil moisture patterns in the Sahel induce local winds (Taylor et al. 2007).. Such winds may in turn affect the likelihood of further rainfall: once a storm has left a pattern of soil moisture on the land surface, this can control the places where rainfall will occur on following days.

We are also using sophisticated chemical tracers to explore the dynamics and mixing in the region; physical processes which control the water budget of the Sahelian zone of West Africa. It is known that global computer models which predict weather and climate have a very unreliable water cycle for the West African region. Typically, climate prediction models even disagree over the sign of predicted rainfall changes in this region for the coming decades - some models predict a wetter climate and some a drier one. We are using the Met Office Unified Model to simulate the water cycle of the region to evaluate the performance of this weather and climate-prediction model, and to explore the fundamental processes of land-atmosphere interaction, which are relevant worldwide.

JET2000.
In the JET2000 experiment, which took place over West Africa late in August 2000, we made unique measurements of the atmospheric structure of the West African Monsoon. We have used the results to investigate the dry and moist convective processes responsible for the maintenance of the African Easterly Jet and the monsoon itself. Some highlights of JET2000 include:

• A new observational analysis of the African Easterly Jet structure, explaining the links between the convective regimes and the monsoon airflows (Parker et al 2005a).
• High resolution analysis of the coupling between the land surface and atmosphere, showing that during the daytime, the state of the lower part of the atmosphere maps closely to the soil moisture distribution, in the northern Sahel (Taylor et al 2003).
• Evaluation of the quality of numerical weather predictions for the region, and an analysis of the importance of different datasets in producing such forecasts (Tompkins et al 2005). It is shown that upper air data from radiosoundings is very important to the generation of good climatic analyses.
• Evaluation of the diurnal cycle of the monsoon winds (Parker et al 2005b). It is shown that the nocturnal monsoon flow can dominate the monsoon circulation, which is very significant given that many upper air measurements are made during the day. The strong diurnal variability also has strong consequences for transport of aerosols and trace gases in the region.

Previously, we used simple, idealised computer modelling (Tian et al 2002, 2003a,b, 2004) to explore the processes which favour the formation of clouds, and eventually rainfall, over UK hills. Under light winds, and particularly in the morning hours, even relatively low hills in the UK can significantly affect the amount of cloud in their vicinity. As part of this work, observations and modelling of coherent structures in the convective boundary layer over the UK, using radar and satellite data, were conducted in a collaborative project with the Chilbolton radar facility. The initiation of thunderstorms over land is also being investigated using case studies and climatology from West Africa, in AMMA (see above).

Transport processes at fronts and in cumulonimbus storms. In this line of work, we developed a sophisticated numerical model of convective cloud transport of trace gases, from which we have derived basic relationships between trace gas properties (such as solubility in water) and bulk convective cloud transport, according to cloud characteristics. More recently we have been exploring the transport of aerosols and their precursors in a marine convective environment (working with Gerry Devine and Ken Carslaw - Devine et al. 2006). We find that the particular structure of the cloud systems, and the relationships between patterns of clouds with sources of aerosols the ocean surface, have a strong bearing on the resulting aerosol distributions in the free atmosphere. For example, rainstorms over the ocean can lead to very strong winds over the water, which increase the emission of trace gases and aerosols from the water into the air. However, the air which is lifted into new clouds, and therefore rises higher into the atmosphere, tends to come from the quieter air outside the windy regions, and may have lower than average concentations of those trace gases and aerosols.

Dynamics of synoptic fronts.
My PhD work at the University of Reading was concerned with the way that cumulonimbus clouds (thunderstorms and heavy showers) influence the behaviour of the kind of cold fronts which we experience over the UK. As part of that work, we came up with the idea of a "diabatic Rossby wave", which is a conceptual model describing the way in which heating of the air in a cloud can cause a front (or a cyclone) to move in a wave-like manner (this term was also coined, coincidentally, by Chris Snyder, who presented the idea at a US conference around the same time). The idea of a diabatic Rossby wave is that if cloud heating occurs to one side of a low level cyclone, then the cyclone will tend to get stronger on that side, and will therefore move in that direction (although the air itself will not move). This is important because cloud processes need to be well represented in order to get the cyclone motion right in a computational forecast model. In recent years, a number of studies have found observational confirmation of cyclones which seem to behave as diabatic Rossby waves.

My postdoctoral work was conducted on secondary frontal cyclones, in conjunction with the group within the JCMM working on the FASTEX project, a field experiment which took place the early part of 1997.

More recently I have worked on the study of tracer transport through frontal zones (Parker 1999), providing an explanation for the formation of 'split' or 'forward-sloping' cold fronts (which account for a significant fraction of UK cold fronts). This work also has implications for the conceptual understanding of pollution transport in frontal systems. My PhD was supervised by Alan Thorpe at the University of Reading Department of Meteorology between 1990 and 1993, having just taken Part III maths at DAMTP in Cambridge. My PhD thesis was concerned with moist convection and its interaction with/generation of atmospheric fronts. Following this I undertook a 3 year NERC-funded postdoctoral position with Alan Thorpe, leading up to FASTEX.

List of publications.

d.j.parker@leeds.ac.uk

My home page.