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Low level marine stratocumulus clouds are a semi-persistent feature of the marine regions adjacent to continents where cold upwelling water reaches the surface. They have a very large influence on the climate of these regions and more widely, yet they are not at all well quantified in models. Furthermore, many key microphysical processes that control the properties of the clouds remain poorly understood. The ambition of VOCALS-UK is to reduce uncertainties in current and future climate projections, especially those associated with marine stratocumulus and coupled ocean-atmosphere processes. It will achieve this through a combination of aircraft measurements; process model studies and climate simulations of the South-East Pacific region as part of a major contribution to the international VOCALS programme.

The international VOCALS (VAMOS Ocean-Cloud-Atmosphere-Land Study) program, coordinated by the VAMOS (Variability of the American MOnsoon Systems) panel of the World Climate Research Programme is a comprehensive observational and modeling programme to study the South-East Pacific (SEP) climate system in unprecedented detail. This international programme has the principal objectives of 1) improving understanding and regional/global model representation of aerosol indirect effects over the SEP; 2) eliminating systematic errors in coupled atmospheric-ocean general circulation models in the region, and delivering improved model simulations and predictions of the coupled climate in the SEP and global impacts of the system variability. VOCALS is organized into two components: a Regional Experiment (VOCALSRex: a field campaign in late 2008), and a Modeling Programme (VOCALS-Mod). Extended observations (e.g. buoys, satellites, cruises) will provide important additional contextual datasets that help to link the field and the modeling components.


The VOCALS-UK Consortium Project

The VOCALS-UK consortium coordinated by Professor Hugh Coe at the University of Manchester consists of investigators from the universities of Manchester, Leeds and Reading, the UK Met Office, FAAM and ARSF. The consortium aims to address the major climate questions:

To address these questions the VOCALS-UK consortium has the following objectives:


VOCALS-UK Measurements

The VOCALS-UK contribution to international field campaign VOCALS-REX, which will take place off the ocast of Chile during October 2008, will add important new measurements to the experimental data set and will complement the existing measurements. In particular the ARSF and FAAM aircraft will provide simultaneous in-situ and remotely sensed measurements of the aerosol and cloud, and their radiative properties. The FAAM aircraft has 70 science flights hours available giving 14 possible sorties, each with a duration of around 5 hours; the ARSF aircraft has 50 flight hours allocated to the project, giving 12 4 hour flights. The VOCALS-UK plans seek to integrate these measurements with those of the other platforms. The broad principle is that the FAAM aircraft concentrates on in situ measurements, jointly with the Met Office, our project partners, and the ARSF on remote sensing (altitude ~ 5 km). Given that the science speeds of the two aircraft are similar (~200kts) it will be possible to obtain in situ and remotely sensed information on the same cloud region at the same time. The range of the FAAM aircraft is longer and so will extend its operations to the west. The FAAM aircraft will also make remote sensing measurements, using the Met Office large radiometers, in conjunction with the C-130 and the ARSF will make some in situ measurements during these periods.


VOCALS-UK Modelling

Two groups of models will be used to investigate process studies and addressing climate questions. In both cases a hierarchy of models will be used to reflect the scientific challenges that cover a wide range of scales.

i) Process Models: Cloud scale processes will be dealt with using Large Eddy Models, these will also be used to provide trajectories for a trajectory following parcel model (ACPIM) which can investigate aerosol-cloud interaction in more detail. Mesoscale to regional scale processes and their effect on the stratocumulus will be studied using the WRF model and aerosol processes, including aerosol-cloud interactions on a regional scale will be studied with WRF-CHEM. The process modeling will be an active collaboration between Manchester, Leeds, and The Met Office.

ii) Climate Models: VOCALS-UK will use a hierarchy of global atmosphere-only and coupled models of varying resolutions (from N48 (~250km) to N320 (~40km) in the atmosphere and from 1.250 to 0.330 in the ocean) to explore the processes operating in the SEP region and how they influence the global climate system. The emphasis on high resolution global coupled models will complement the regional modeling activities in the international VOCALS-Mod programme. The climate modeling activities will be performed by NACS-Climate at Reading.

Sensitivity experiments and multi-decadal integrations with a suite of models at different resolutions (HadCM3, HadGEM, HiGEM) will help determine the dominant regulatory processes and feedbacks in the SEP region, their dependence on model resolution, and their implications for the tropical Pacific and ENSO. Model error-growth analysis of ensembles of short, high-resolution global atmospheric integrations (NUGAM, at N320) will be used to understand the nature of model-generated tendencies, model systematic errors and their dependence on processes identified and constrained in the observational campaign. The cross-validation between model integration at resolutions from N320 to N48 will provide information on the robustness of simulated process as well as on persistent model biases. Their evaluation will make use of the results from the observational campaign, and link with other modelling efforts of the wider VOCALS community.


Further Information

Additional information about the international VOCALS project and VOCALS-UK may be found on the project websites listed below. These sites include detailed information on the science problems addressed by VOCALS, and contain planning information and other documents of relevance to project participants.

International VOCALS Project Website

VOCALS-UK Project Website