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Devon, PA, United States

The Met Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Innovation and Skills and a member of the Public Data Group. The chief executive is Rob Varley and the chief scientist is Dame Julia Slingo. The Met Office makes meteorological predictions across all timescales from weather forecasts to climate change. The Hadley Centre for Climate Prediction and Research and the National Meteorological Library and Archive are part of the Met Office. At the Met Office headquarters at Exeter in Devon is the Met Office College, which handles the training for internal personnel and forecasters from around the world. Wikipedia.

Rowell D.P.,UK Met Office
Journal of Climate | Year: 2013

This study provides an overview of the state of the art of modeling SST teleconnections to Africa and begins to investigate the sources of error. Data are obtained from the Coupled Model Intercomparison Project (CMIP) archives, phases 3 and 5 (CMIP3 and CMIP5), using the "20C3M" and "historical" coupled model experiments. A systematic approach is adopted, with the scope narrowed to six large-scale regions of sub-Saharan Africa within which seasonal rainfall anomalies are reasonably coherent, along with six SST modes known to affect these regions. No significant nonstationarity of the strength of these 6X6 teleconnections is found in observations. The capability of models to represent each teleconnection is then assessed (whereby half the teleconnections have observed SST-rainfall correlations that differ significantly from zero). A few of these teleconnections are found to be relatively easy to model, while a few more pose substantial challenges to models and many others exhibit a wide variety of model skill. Furthermore, some models perform consistently better than others, with the best able to at least adequately simulate 80%-85% of the 36 teleconnections. No improvement is found between CMIP3 and CMIP5. Analysis of atmosphere-only simulations suggests that the coupled model teleconnection errors may arise primarily from errors in their SST climatology and variability, although errors in the atmospheric component of teleconnections also play a role. Last, no straightforward relationship is found between the quality of a model's teleconnection to Africa and its SST or rainfall biases or its resolution. Perhaps not surprisingly, the causes of these errors are complex, and will require considerable further investigation. Source

An experimental convection-permitting ensemble prediction system (EPS) has recently been developed at the Met Office where the analysis uncertainty is estimated by means of an ensemble transform Kalman filter (ETKF). In this paper, the author reports on a case study where mismatches between the analysis perturbations and the perturbations coming from the lateral boundaries lead to the generation of significant spurious per- turbations in the ensemble forecasts of the surface pressure. To alleviate ensemble perturbation mismatches originating from the ensemble technique, he tests a so-called scale-selective ETKF where a revised transform matrix is applied only to the small-scale component of the high-resolution forecasts, while the large-scale component of the analysis perturbations is taken from the driving EPS. Results show that the new approach successfully removes the spurious perturbations in the surface pressure fields and also provides some benefits in the precipitation forecasts for the case studied. An examination of ensemble-derived forecast error covariances reveals that ensemble perturbation mismatches at the lateral boundaries tend to decrease the degree of balance between the mass field and the rotational wind field and to produce more compact horizontal and vertical correlations. Finally, the limitations of the scale-selective approach and future directions are discussed. Source

The Hindu Kush, Karakoram, and Himalaya (HKH) region has a negative average glacial mass balance for the present day despite anomalous possible gains in the Karakoram. However, changes in climate over the 21st century may influence the mass balance across the HKH. This study uses regional climate modelling to analyse the implications of unmitigated climate change on precipitation, snowfall, air temperature and accumulated positive degree days for the Hindu Kush (HK), Karakoram (KK), Jammu-Kashmir (JK), Himachal Pradesh and West Nepal regions (HP), and East Nepal and Bhutan (NB). The analysis focuses on the climate drivers of change rather than the glaciological response. Presented is a complex regional pattern of climate change, with a possible increase in snowfall over the western HKH and decreases in the east. Accumulated degree days are less spatially variable than precipitation and show an increase in potential ablation in all regions combined with increases in the length of the seasonal melt period. From the projected change in regional climate the possible implications for future glacier mass balance are inferred. Overall, within the modelling framework used here the eastern Himalayan glaciers (Nepal-Bhutan) are the most vulnerable to climate change due to the decreased snowfall and increased ablation associated with warming. The eastern glaciers are therefore projected to decline over the 21st Century despite increasing precipitation. The western glaciers (Hindu Kush, Karakoram) are expected to decline at a slower rate over the 21st century in response to unmitigated climate compared to the glaciers of the east. Importantly, regional climate change is highly uncertain, especially in important cryospheric drivers such as snowfall timing and amounts, which are poorly constrained by observations. Data are available from the author on request. © Author(s) 2014. Source

Staniforth A.,UK Met Office
Quarterly Journal of the Royal Meteorological Society | Year: 2014

A quartet of dynamically consistent approximate models of the global atmosphere in non-spherical coordinates has recently been developed, according to whether approximations of shallow and/or quasi-hydrostatic nature are made. A model is considered to be dynamically consistent if it formally preserves conservation principles for axial angular momentum, energy and potential vorticity. The development of these approximate models involved detailed examination of conservation budgets to determine which terms to omit, modify, or retain in the equations for the three components of momentum, according to the type of approximation made. An alternative, complementary, derivation of this quartet of approximate models is developed herein using Hamilton's principle. With this approach, a single term in the Lagrangian is identified, which can then be optionally modified to apply the quasi-hydrostatic approximation via an on-off switch. As in the previous work, application of the shallow-atmosphere approximation is achieved by choosing an orthogonal curvilinear coordinate system having an appropriate shallow metric. Application of Hamilton's principle and Noether's theorem then intrinsically preserves the conservation principles for axial angular momentum, energy and potential vorticity. This obviates the need to examine conservation budgets to determine which terms to omit, modify, or retain in the equations for the three components of momentum; everything just falls into place via the application of variational calculus. The resulting unified equation set is then identical to that previously obtained by trial and error examination of conservation budgets. © 2013 Royal Meteorological Society. Source

An atmospheric general circulation model is forced with observed monthly sea surface temperature and sea ice boundary conditions, as well as forcing agents that vary in time, for the period 1979-2008. The simulations are then repeated with various forcing agents, individually and in combination, fixed at preindustrial levels. The simple experimental design allows the diagnosis of the model's global and regional time-varying effective radiative forcing from 1979 to 2008 relative to preindustrial levels. Furthermore the design can be used to (i) calculate the atmospheric model's feedback/sensitivity parameters to observed changes in sea surface temperature and (ii) separate those aspects of climate change that are directly driven by the forcing from those driven by large-scale changes in sea surface temperature. It is shown that the atmospheric response to increased radiative forcing over the last 3 decades has halved the global precipitation response to surface warming. Trends in sea surface temperature and sea ice are found to contribute only ̃60% of the global land, Northern Hemisphere, and summer land warming trends. Global effective radiative forcing is ̃1.5Wm-2in this model, with anthropogenic and natural contributions of ̃1.3 and ̃0.2 W m-2, respectively. Forcing increases by ̃0.5 W m-2decade-1 over the period 1979-2008 or ̃0.4 W m-2 decade-1 if years strongly influenced by volcanic forcings-which are nonlinear with time-are excluded from the trend analysis. Aerosol forcing shows little global decadal trend due to offsetting regional trends whereby negative aerosol forcing weakens in Europe and North America but continues to strengthen in Southeast Asia. © 2014 American Meteorological Society. Source

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