Claire Witham

Claire Witham
Met Office · Observations R&D

PhD

About

67
Publications
19,508
Reads
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2,014
Citations
Citations since 2017
24 Research Items
1002 Citations
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Introduction
Claire Witham works at the UK Met Office, where she is Head of the Observations Research and Development team. Claire's previous research has been in the areas of Meteorology, Volcanology and Climatology. She has been involved in the European 'EUROVOLC' and 'FUTUREVOLC' projects and the NERC VPLUS and R4ASH projects amongst others.
Additional affiliations
January 2005 - present
Met Office
Position
  • Science Manager
September 2000 - December 2004
University of Cambridge
Position
  • PhD

Publications

Publications (67)
Preprint
Full-text available
Volcanic eruptions can emit large quantities of sulphur dioxide (SO 2 ) into the atmosphere, which can be harmful to people and the environment. Aircraft encounters with a volcanic SO 2 cloud could represent a health hazard to crew and passengers onboard, depending on the dose of SO 2 encountered. The recommended SO 2 concentration threshold set by...
Article
Full-text available
We have developed an aggregation scheme for use with the Lagrangian atmospheric transport and dispersion model NAME (Numerical Atmospheric Dispersion modelling Environment), which is used by the London Volcanic Ash Advisory Centre (VAAC) to provide advice and guidance on the location of volcanic ash clouds to the aviation industry. The aggregation...
Article
Full-text available
Between 27 June and 14 July 2019 aerosol layers were observed by the United Kingdom (UK) Raman lidar network in the upper troposphere and lower stratosphere. The arrival of these aerosol layers in late June caused some concern within the London Volcanic Ash Advisory Centre (VAAC) as according to dispersion simulations the volcanic plume from the 21...
Article
The Eyjafjallajökull eruption of 2010 demonstrated the far-reaching impact of ash clouds and the vulnerability of our jet-based society to them, prompting a review of procedures to detect, warn, and forecast ash cloud hazards to aviation. The years since 2010 have seen marked improvements in satellite technology, more accurate ash-dispersion models...
Article
Full-text available
Volcanic air pollution from both explosive and effusive activity can affect large populations as far as thousands of kilometers away from the source, for days to decades or even centuries. Here, we summarize key advances and prospects in the assessment of health hazards, effects, risk, and management. Recent advances include standardized ash assess...
Article
Full-text available
We present a Bayesian inversion method for estimating volcanic ash emissions using satellite retrievals of ash column load and an atmospheric dispersion model. An a priori description of the emissions is used based on observations of the rise height of the volcanic plume and a stochastic model of the possible emissions. Satellite data are processed...
Technical Report
Volcanic activity can release large quantities of sulphur dioxide (SO2) into the atmosphere from explosive and effusive eruptions. Elevated concentrations of SO2 pose a potential health hazard to passengers and crew and may impact aircraft components and hence maintenance cycles. The exposure and level of potential risk to air traffic is determined...
Article
Full-text available
Volcanic eruptions can cause significant disruption to society, and numerical models are crucial for forecasting the dispersion of erupted material. Here we assess the skill and limitations of the Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME) in simulating the dispersion of the sulfur dioxide (SO2) cloud from the 21–22...
Preprint
Full-text available
Between 27 June and 14 July 2019 aerosol layers were observed by the United Kingdom (UK) Raman lidar network in the upper troposphere and lower stratosphere. The arrival of these aerosol layers in late June caused some concern within the London Volcanic Ash Advisory Centre (VAAC) as according to dispersion simulations the volcanic plume from the 21...
Preprint
Full-text available
We have developed an aggregation scheme for use with the Lagrangian atmospheric transport and dispersion model NAME, which is used by the London Volcanic Ash Advisory Centre (VAAC) to provide advice and guidance on the location of volcanic ash clouds to the aviation industry. The aggregation scheme uses the fixed pivot technique to solve the Smoluc...
Article
Ash, gases and particles emitted from volcanic eruptions cause disruption to air transport, but also have negative impacts on respiratory and cardiovascular health. Exposure to sulphur dioxide (SO2) and sulphate (SO4) aerosols increases the risk of mortality, and respiratory and cardiovascular hospital admissions. Ash and gases can be transported o...
Preprint
Full-text available
Volcanic eruptions can cause significant disruption to society and numerical models are crucial for forecasting the dispersion of erupted material. Here we assess the skill and limitations of the Met Office’s Numerical Atmospheric-dispersion Modelling Environment (NAME) in simulating the dispersion of the sulfur dioxide (SO2) cloud from the 21–22 J...
Article
For the first time since the Chernobyl accident, detectable concentrations of ruthenium-106 were measured across Europe in September and October 2017. The source of this radioactive cloud remains unconfirmed. In this paper we present a forensic inverse modelling study to simultaneously estimate the source location, timing and magnitude of the unexp...
Article
Full-text available
It has been 10 years since the ash cloud from the eruption of Eyjafjallajökull caused unprecedented disruption to air traffic across Europe. During this event, the London Volcanic Ash Advisory Centre (VAAC) provided advice and guidance on the expected location of volcanic ash in the atmosphere using observations and the atmospheric dispersion model...
Article
Full-text available
Following publication of the original article Witham et al., 2020, it was noticed a mistake of copyright holder name.
Article
Full-text available
Abstract A 3 day exercise simulating unrest and a large explosive eruption at Katla volcano, Iceland, was conducted in January 2016. A large volume of simulated data based on a complex, but realistic eruption scenario was compiled in advance and then transmitted to exercise participants in near-real time over the course of the exercise. The scenari...
Technical Report
Full-text available
This paper describes the development of a scheme to parametrize tropospheric convection in the Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME). A Lagrangian dispersion model, NAME is generally driven by meteorological data from an NWP model. The new convection scheme is intended to represent particle transport due to the...
Conference Paper
Full-text available
The Atmospheric Dispersion Modelling Liaison Committee (ADMLC) is a committee composed of dispersion modelling experts and practitioners primarily, but not exclusively, from various government agencies in the UK and Ireland. Its main aim is to review current issues and facilitate the exchange of knowledge in atmospheric dispersion modelling and rel...
Article
Full-text available
This paper presents a study of haze in Singapore caused by biomass burning in Southeast Asia over the 6-year period from 2010 to 2015, using the Numerical Atmospheric-dispersion Modelling Environment (NAME), which is a Lagrangian dispersion model. The major contributing source regions to the haze are identified using forwards and backwards model si...
Preprint
Full-text available
On 5-7 February 2019, the UK Met Office hosted a workshop to bring together the Volcano Observatories (VOs), Volcanic Ash Advisory Centres (VAACs) and Volcanological Research Institutes (VRI) in Europe. This workshop was part of the H2020 EUROVOLC project and the networking Activity “Connecting the volcanological community with VAACs”. The workshop...
Article
Full-text available
This paper presents a study of haze in Singapore caused by biomass burning in Southeast Asia over the six year period from 2010 to 2015, using the Lagrangian dispersion model, NAME. The major contributing source regions are shown to be Riau, Peninsular Malaysia, South Sumatra, and Central and West Kalimantan. However, we see differences in haze co...
Poster
Full-text available
The poster details a large transboundary volcanic eruption exercise conducted in 2016 by the FUTUREVOLC project. The exercise simulated an eruption at Katla and tested the response to this from the local volcano observatory, civil protection, VAAC and the scientific community.
Article
Full-text available
The 2014-2015 Holuhraun eruption in Iceland, emitted ~11 Tg of SO2 into the troposphere over 6 months, and caused one of the most intense and widespread volcanogenic air pollution events in centuries. This study provides a number of source terms for characterisation of plumes in large fissure eruptions, in Iceland and elsewhere. We characterised th...
Article
Full-text available
On 16–17 September 2013 strong surface winds over tephra deposits in southern Iceland led to the resus-pension and subsequent advection of significant quantities of volcanic ash. The resulting resuspended ash cloud was transported to the southeast over the North Atlantic Ocean and, due to clear skies at the time, was exceptionally well observed in...
Article
Full-text available
This study examines the sensitivity of atmospheric dispersion model forecasts of volcanic ash clouds to the physical characteristics assigned to the particles. We show that the particle size distribution (PSD) used to initialise a dispersion model has a significant impact on the forecast of the mass loading of the ash particles in the atmosphere. T...
Article
The Lagrangian atmospheric dispersion model NAME (Numerical Atmospheric-dispersion Modelling Environment), has been used to simulate the formation and transport of PM10 over North-West Europe in 2008. The model has been evaluated against UK measurement data and been shown to adequately represent the observed PM10 at rural and urban sites on a daily...
Article
Full-text available
On the 16–17 September 2013 strong surface winds over tephra deposits in southern Iceland led to the resuspension and subsequent advection of significant quantities of volcanic ash. The resulting resuspended ash cloud was transported to the south-east over the North Atlantic Ocean and, due to clear skies at the time, was exceptionally well observed...
Article
Full-text available
Transboundary smoke haze caused by biomass burning frequently causes extreme air pollution episodes in maritime and continental Southeast Asia. With millions of people being affected by this type of pollution every year, the task to introduce smoke haze related air quality forecasts is urgent. We investigate three severe haze episodes: June 2013 in...
Technical Report
Full-text available
When using dispersion models to predict the quantitative transport of volcanic ash, source term parameters defining the emission characteristics are required. Retrievals of ash column loadings can be calculated using data from satellite based instruments such as the SEVIRI (Spinning En- hanced Visible and Infrared Imager) instrument on-board the MS...
Article
Full-text available
Here we present high frequency long-term observations of ethane, benzene and methyl chloride from the AGAGE Ragged Point, Barbados, monitoring station made using a custom built GC-MS system. Our analysis focuses on the first three years of data (2005-2007) and on the interpretation of periodic episodes of high concentrations of these compounds. We...
Article
Full-text available
The 2014–2015 Bárðarbunga-Veiðivötn fissure eruption at Holuhraun produced about 1.5 km3 of lava, making it the largest eruption in Iceland in more than 200 years. Over the course of the eruption, daily volcanic sulfur dioxide (SO2) emissions exceeded daily SO2 emissions from all anthropogenic sources in Europe in 2010 by at least a factor of 3. We...
Article
Full-text available
Volcanic eruptions take place in Iceland about once every three to five years. Ash emissions from these eruptions can cause significant disruption to air traffic over Europe and the North Atlantic as is evident from the 2010 eruption of Eyjafjallajökull. Sulfur dioxide (SO2) is also emitted by volcanoes, but there are no criteria to define when air...
Poster
Full-text available
In March 2011, the combined effects of an earthquake and a tsunami resulted in serious damage to the Fukushima Dai-ichi (Fukushima 1) nuclear power plant on the east coast of Japan. As a result large amounts of radioactive material were released into the atmosphere. Although much of the radioactive material was transported eastwards over the Pacifi...
Article
Full-text available
Recent eruptions in Iceland and Chile have demonstrated that volcanic ash problems persist long after an eruption. For this reason, ash dispersion models are being extended to include ash remobilisation. Critical to these models is knowledge of the ash source, as well as the particle sizes that can be mobilised under different wind and moisture con...
Poster
Full-text available
Operational smoke-haze dispersion modelling with NAME at the Meteorological Service Singapore
Article
Infrared satellite measurements were used to track the volcanic plume from Grímsvötn, Iceland in 2011. Following the explosive eruption, the plume was sheared by the atmosphere into two distinct volcanic clouds, one was ash-rich and the other was mainly composed of sulphur dioxide (SO2) gas. Satellite retrievals of the volcanic ash were found to be...
Conference Paper
FUTUREVOLC is a collaborative project funded through the FP7 Environment Supersite Concept call encompassing 26 partners in 10 countries. The main objectives of FUTUREVOLC are to establish an integrated volcanological monitoring procedure through European collaboration, develop new methods to evaluate volcanic crises, increase scientific understand...
Conference Paper
Full-text available
The eruption of Eyjafjallajökull during April - May 2010 and Grímsvötn in May 2011, Iceland, caused the widespread dispersion of volcanic ash across the NE Atlantic, and ultimately into UK and European airspace. This resulted in thousands of flights to and from affected countries across Europe to be cancelled. The Met Office, UK, is the home of the...
Article
Routine measurements of a wide range of trace gases have been made at the coastal monitoring site of Ragged Point, Barbados, since the late 1970's. Here we report on the observation of events of high concentrations of non-methane hydrocarbons (NMHC) and ozone depleting substances (ODS) measured at this site during August - October annually. We use...
Conference Paper
Full-text available
An Icelandic blizzard on March 6, 2013, left Reykjavik blanketed in " brown snow ". This event was initially attributed to remobilization and later deposition of ash from the 2011 Grimsvötn eruption, approximately 200 km to the east. We collected samples from the snow surface on March 7 to determine the source, size distribution and characteristics...
Article
Full-text available
The UK Met Office's Numerical Atmospheric-dispersion Modeling Environment (NAME) is used both operationally and for research investigations. It has previously been used to model volcanic ash at the London Volcanic Ash Advisory Centre (VAAC), including that from the eruptions in Iceland of Eyjafjallajökull in 2010 and Gr'imsvötn in 2011. In this pap...
Article
Full-text available
During the 2010 eruption of Eyjafjallajökull, improvements were made to the modeling procedure at the Met Office, UK, enabling peak ash concentrations within the volcanic cloud to be estimated. In this paper we describe the ash concentration forecasting method, its rationale and how it evolved over time in response to new information and user requi...
Article
Full-text available
Eyjafjallajökull, a volcano in southern Iceland, erupted explosively in April and May 2010 depositing ash over a region of more than 3000 km2 to the east and southeast of the volcano. This deposited ash has been frequently remobilized by the wind causing concern for the health of Icelanders living in the region. An investigation was carried out to...
Article
Full-text available
The agricultural commodity market is sensitive to variations in weather and climate, which can disrupt supply and cause price fluctuations. Some of the key positive and negative impacts of climate change on agricultural commodities, using the examples of wheat and barley, are identified; of particular significance are temperature changes, water ava...
Article
Full-text available
The diversity of processes involved in manufacturing and the range of commodities that are traded on the global market makes analysing climate change impacts a challenging task. A methodology for systematically evaluating the large-scale impacts of climate change on manufactured goods in the global market is presented. The effects of climate change...
Poster
Full-text available
Modelling study/framework aimed at investigating probabilistically the impact of a large Icelandic flood lava eruption.
Article
Odour pollution is generally regarded as a local issue. The long range transport of odorants at levels sufficient to generate odour complaints far from their source is not normally given serious consideration, let alone subject to legislation. We argue that such an event led to an odour incident affecting much of southern and eastern England and us...
Conference Paper
Full-text available
The May 2011 eruption of Grímsvötn, Iceland, was short-lived but powerful. Tephra was transported to the UK, where it could be identified in rainwater, sticky-tape samples and air quality data. We present analysis of timings and extent of tephra transport and compare them to predictions from the NAME dispersion model. Daily rainwater samples collec...
Article
Full-text available
Prolonged disruption to aviation during the April–May 2010 eruption of Eyjafjallajökull, Iceland resulted in pressure to predict volcanic ash plume concentrations for the purpose of allowing aircraft to fly in regions with low ash contamination. Over the past few decades there have been a number of incidents where aircraft have encountered volcanic...
Article
Episodic peak ozone levels over the 1990–2007 period appear to have declined strongly whilst annual mean daily maximum levels have risen over the same period at monitoring sites within the midlands regions of the UK. Sensitivity studies carried out with a photochemical trajectory model have shown that European policies to control Volatile Organic C...
Article
Full-text available
Continuous high-frequency measurements of atmospheric molecular hydrogen have been made at Mace Head atmospheric research station on the west coast of Ireland from March 1994 to December 2008. The presented data provides information on long term trends and seasonal cycles of hydrogen in background northern hemispheric air. Individual measurements h...
Article
Full-text available
A Lagrangian dispersion model has been used to predict daily sulphate aerosol in 2006 at five UK rural measurement sites and hourly nitrate aerosol in April 2003 at Harwell (UK). The sensitivity of aqueous phase sulphate production to the meteorological input has been investigated. Large differences were found between cloud fraction and cloud liqui...
Article
The existing generation of satellite instruments (such as SCIAMACHY and AIRS) have allowed the retrieval of atmospheric mixing ratios of carbon dioxide. This data can be used to investigate carbon fluxes between the surface and the atmosphere. This information can compliment existing flux information from the high precision but low density network...
Article
A moving air parcel trajectory model has been used to estimate the mid-afternoon mass concentrations of a number of suspended particulate matter (PM) components for each day of 2006 for a rural location, Harwell, Oxfordshire, in the southern UK. A large number of equally probable and randomly selected 96-h 3-dimensional air mass trajectories were u...
Article
Full-text available
The growth of background levels of atmospheric methane showed a marked increase in both hemispheres in 2007. This paper looks at the data from a range of observation stations that monitor methane at high frequency, including Barrow (Alaska), Ragged Point (Barbados), Trinidad Head (California), Cape Grim (Australia), Cape Matatula (Samoa), Gosan (So...
Article
Full-text available
As predicted, bluetongue arrived in the UK in 2007. Here, John Gloster and colleagues investigate the meteorological parameters that allowed this incursion into the UK and discuss key issues related to the disease's possible re-establishment in 2008.
Article
Full-text available
Unusually high levels of PM10 were observed in the UK in May 2006 and September 2002. This paper investigates the possible contribution of long-range transport of smoke from widespread agricultural burning and forest fires in western Russia to these air pollution episodes. The Lagrangian dispersion model NAME is run in both forwards and backwards m...
Article
Full-text available
The robustness of the Numerical Atmospheric-dispersion Modelling Environment (NAME) for forecasting the dispersion of volcanic ash clouds is investigated by comparing the output from different Volcanic Ash Advisory Centre (VAAC) models initialised using the parameters for the 2004 Grimsvötn, Iceland, volcanic eruption. London, Darwin, Washington, M...
Article
Full-text available
A new database on human mortality and morbidity, and civil evacuations arising from volcanic activity is presented. The aim is to quantify the human impacts of volcanic phenomena during the 20th Century. Data include numbers of deaths, injuries, evacuees and people made homeless, and the nature of the associated volcanic phenomena. The database has...
Article
Full-text available
Tephra in plumes can scavenge and thereby rapidly deposit volatiles including sulphur, halogen and metal species. These may then be leached (e.g. by rainfall), potentially releasing heavy loadings to soils and water bodies. Several eruptions have resulted in contamination of pasture, sometimes with serious impacts on livestock. Water quality has al...
Article
Full-text available
1783/4 has been recognised as a mortality crisis year in the population history of England. This demographic incident coincides with the Laki Craters eruption, Iceland, which began in June 1783 and fumigated many parts of Europe with volcanic gases and particles. Many reports and proxy climate records implicate the volcanic cloud in meteorological...
Article
A tropospheric plume from a large basaltic fissure eruption similar to the 934 AD Eldgja or 1783 AD Laki Craters eruptions would be expected to contain acid gases and aerosols including SO2, H2SO4, HCl