Quantification of the importance of wind drift to the surface distribution of orographic rain on the occasion of the extreme Cockermouth flood in Cumbria

Lean, Humphrey; Browning, K. A.

doi:10.1002/qj.2024

Cited by 12 publications

(12 citation statements)

References 41 publications

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“…As a result, there was serious flooding in January 1927 and November 1929 (Table ), as well as other notable autumnal floods in 1894 and 1944. These conditions are characteristic of upland areas of the UK where positive autumn/winter NAO anomalies result in prolonged frontal/orographically intensified rainfall over large areas (Figure ) (Burt, ; Leaning and Browning, ). Rainfall of this type can occur at any time of the year, but is most common during the autumn (October–November) when sea surface temperatures are high and southwest winds dominant (Webb, ), associated with ‘atmospheric rivers’ of warm, moist air sourced from the subtropics (Lavers et al ., ).…”

Section: Resultsmentioning

confidence: 99%

The chronology and the hydrometeorology of catastrophic floods on Dartmoor, South West England

Foulds

Macklin

Brewer

2013

Hydrological Processes

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Abstract:Extreme floods are the most widespread and often the most fatal type of natural hazard experienced in Europe, particularly in upland and mountainous areas. These 'flash flood' type events are particularly dangerous because extreme rainfall totals in a short space of time can lead to very high flow velocities and little or no time for flood warning. Given the danger posed by extreme floods, there are concerns that catastrophic hydrometeorological events could become more frequent in a warming world. However, analysis of longer term flood frequency is often limited by the use of short instrumental flow records (last 30-40 years) that do not adequately cover alternating flood-rich and flood-poor periods over the last 2 to 3 centuries. In contrast, this research extends the upland flood series of South West England (Dartmoor) back to ca AD 1800 using lichenometry. Results show that the period 1820 to mid-1940s was characterized by widespread flooding, with particularly large and frequent events in the mid-to-late 19th and early 20th centuries. Since ca 1850 to 1900, there has been a general decline in flood magnitude that was particularly marked after the 1930s/mid-1940s. Local meteorological records show that: (1) historical flood-rich periods on Dartmoor were associated with high annual, seasonal and daily rainfall totals in the last quarter of the 19th century and between 1910 and 1946, related to sub-decadal variability of the North Atlantic Oscillation and receipt of cyclonic and southerly weather types over the southwest peninsula; and (2) the incidence of heavy daily rainfall declined notably after 1946, similar to sedimentary archives of flooding. The peak period of flooding on Dartmoor predates the beginning of gauged flow records, which has practical implications for understanding and managing flood risk on rivers that drain Dartmoor.

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Section: Resultsmentioning

confidence: 99%

The chronology and the hydrometeorology of catastrophic floods on Dartmoor, South West England

Foulds

Macklin

Brewer

2013

Hydrological Processes

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“…We make use of prognostic rain, which allows three-dimensional advection of the rain mass mixing ratio. This has been shown to improve precipitation distributions over and around mountainous regions, especially with the smaller grid spacings used in the RAL configurations (Lean et al, 2008;Lean and Browning, 2013). Prognostic graupel has also been included, this allows for the explicit representation of a second, more dense ice category which is useful for hail 1 https://code.metoffice.gov.uk/trac/socrates 6 https://doi.org/10.5194/gmd-2019-130 Preprint.…”

Section: Microphysicsmentioning

confidence: 99%

The first Met Office Unified Model/JULES Regional Atmosphere and Land configuration, RAL1

Bush¹,

Allen²,

Bain³

et al. 2019

Preprint

107

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Abstract. In this paper we define the first "Regional Atmosphere and Land" (RAL) science configuration for kilometre scale modelling using the UM and JULES. "RAL1" defines the science configuration of the dynamics and physics schemes of the atmosphere and land. This configuration will provide a model baseline for any future weather or climate model developments to be described against and it is the intention that from this point forward significant changes to the system will be documented in literature. This is reproducing the process used for global configurations of the UM which was first documented as a science configuration in 2011. While it is our goal to have a single defined configuration of the model that performs effectively in all regions, this has not yet been possible. Currently we define two sub-releases, one for mid-latitudes (RAL1-M) and one for tropical regions (RAL1-T). The differences between RAL1-M and RAL1-T are documented and where appropriate, we define how the model configuration relates to the corresponding configuration of the global forecasting model.

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“…However, with current computing power, and in order to provide more skillful regional forecasts, operational weather centres now run limited area models at horizontal grid lengths as small as a few kilometres. For example, the 1.5-km grid length configuration of the Met Office Unified Model provides high-resolution forecasts of severe precipitation and fog for domains covering the UK (Lean and Browning 2012).…”

Section: Introductionmentioning

confidence: 99%

A Length Scale Defining Partially-Resolved Boundary-Layer Turbulence Simulations

Beare

2013

Boundary-Layer Meteorol

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Numerical weather prediction (NWP) model forecasts at horizontal grid lengths in the range of 100 m to 1 km are now possible. Within this range of grid lengths, the convective boundary layer is partially resolved and thus in the socalled 'grey zone'. For simulations in the grey zone, numerical dissipation sources from both the advection scheme and the subgrid model are likely to be significant. Until now, these effects have not been incorporated fully into our understanding of the grey zone. In order to quantify these effects, a dissipation length scale is defined based on the second moment of the turbulent kinetic energy (TKE) spectrum.An ensemble of simulations of a convective boundary layer are performed using a large-eddy model across the grey-zone resolutions and for a range of subgrid model, advection scheme and vertical grid configurations. The dissipation length scale distinguishes the effects of the different model configurations in the grey zone. In the middle of the boundary layer, the resolved TKE is strongly controlled by the numerical dissipation. This leads to a similarity law for the resolved TKE in the grey zone using the dissipation length scale. A new definition of the grey zone emerges where the inversion depth and dissipation length scale are the same size. This contrasts with the typical definition using the horizontal grid length. At the inversion, however, the variation of the dissipation length scale with grid length is less predictable, reflecting significant challenges for modelling entrainment in the grey zone. The dissipation length scale is thus a simple diagnostic to aid both NWP and large-eddy modellers in understanding the grey zone.

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Quantification of the importance of wind drift to the surface distribution of orographic rain on the occasion of the extreme Cockermouth flood in Cumbria

Cited by 12 publications

References 41 publications

The chronology and the hydrometeorology of catastrophic floods on Dartmoor, South West England

The chronology and the hydrometeorology of catastrophic floods on Dartmoor, South West England

The first Met Office Unified Model/JULES Regional Atmosphere and Land configuration, RAL1

A Length Scale Defining Partially-Resolved Boundary-Layer Turbulence Simulations

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