Publications


A new view of seasonal forecast skill: Bounding boxes from the DEMETER ensemble forecasts

Tellus, Series A: Dynamic Meteorology and Oceanography 57 (2005) 265-279

A Weisheimer, LA Smith, K Judd

Insight into the likely weather several months in advance would be of great economic and societal value. The DEMETER project has made coordinated multi-model, multi-initial-condition simulations of the global weather as observed over the last 40 years; transforming these model simulations into forecasts is non-trivial. One approach is to extract merely a single forecast (e.g. best-first-guess) designed to minimize some measure of forecast error. A second approach would be to construct a full probability forecast. This paper explores a third option, namely to see how often this collection of simulations can be said to capture the target value, in the sense that the target lies within the bounding box of the forecasts. The DEMETER forecast system is shown to often capture the 2-m temperature target in this sense over continental areas at lead times up to six months. The target is captured over 95% of the time at over a third of the grid points and maintains a bounding box range less than that of the local climatology. Such information is of immediate value from a user's perspective. Implications for the minimum ensemble size as well as open foundational issues in translating a set of multi-model multi-initial-condition simulations into a forecast are discussed; in particular, those involving 'bias correction' are consider. Copyright © Blackwell Munksgaard, 2005.


Representing model uncertainty in weather and climate prediction

ANNUAL REVIEW OF EARTH AND PLANETARY SCIENCES 33 (2005) 163-193

TN Palmer, GJ Shutts, R Hagedorn, E Doblas-Reyes, T Jung, M Leutbecher


Quantum reality complex numbers, and the meteorological butterfly effect

BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY 86 (2005) 519-+

TN Palmer


The rationale behind the success of multi-model ensembles in seasonal forecasting - II. Calibration and combination

TELLUS SERIES A-DYNAMIC METEOROLOGY AND OCEANOGRAPHY 57 (2005) 234-252

FJ Doblas-Reyes, R Hagedorn, TN Palmer


More power needed to probe cloud systems

NATURE 434 (2005) 271-271

TN Palmer


Gradient free descent: Shadowing, and state estimation using limited derivative information

Physica D: Nonlinear Phenomena 190 (2004) 153-166

K Judd, L Smith, A Weisheimer

Shadowing trajectories can play an important role in assessing the reliability of forecasting models, they can also play an important role in providing state estimates for ensemble forecasts. Gradient descent methods provide one approach for obtaining shadowing trajectories, which have been shown to have many useful properties. There remains the important question whether shadowing trajectories can be found in very high-dimensional systems, like weather and climate models. The principle impediment is the need to compute the derivative (or adjoint) of the system dynamics. In this paper we investigate gradient descent methods that use limited derivative information. We demonstrate the methods with an application to a moderately high-dimensional system using no derivative information at all. © 2003 Elsevier B.V. All rights rserved.


Nonlinear dynamics of the climate system

CLIMATE IN HISTORICAL TIMES: TOWARDS A SYNTHESIS OF HOLOCENCE PROXY DATA AND CLIMATE MODELS (2004) 13-41

K Dethloff, A Rinke, D Handorf, A Weisheimer, W Dorn


Internal climate variability in global and regional climate models

CLIMATE IN HISTORICAL TIMES: TOWARDS A SYNTHESIS OF HOLOCENCE PROXY DATA AND CLIMATE MODELS (2004) 365-382

D Handorf, W Dorn, K Dethloff, A Rinke, A Weisheimer


Development of a European multimodel ensemble system for seasonal-to-interannual prediction (DEMETER)

BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY 85 (2004) 853-+

TN Palmer, A Alessandri, U Andersen, P Cantelaube, M Davey, P Delecluse, M Deque, E Diez, FJ Doblas-Reyes, H Feddersen, R Graham, S Gualdi, JF Gueremy, R Hagedorn, M Hoshen, N Keenlyside, M Latif, A Lazar, E Maisonnave, V Marletto, AP Morse, B Orfila, P Rogel, JM Terres, MC Thomson


A granular permutation-based representation of complex numbers and quaternions: elements of a possible realistic quantum theory

PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 460 (2004) 1039-1055

TN Palmer


Improved radio occultation sounding of the Arctic atmosphere using simulations with a high resolution atmospheric model

Physics and Chemistry of the Earth 29 (2004) 277-286

V Kunitsyn, V Zakharov, K Dethloff, A Weisheimer, M Gerding, R Neuber, A Rinke, I Hebestadt

Radio occultation experiments have been simulated for the Arctic region on the basis of the regional atmospheric model HIRHAM4. Irregular structures in the atmosphere produce a violation of the quasi-sphericity in the radio signal propagation and exert a strong influence on the accuracy of atmospheric profiles retrieved by the radio occultation technique. Errors in radio occultation data are spatially localised and associated with gradients in atmospheric structures. Local errors reach 2% in retrieved profiles of refractivity corresponding to an error of 6 K in temperature. Therefore mesoscale variations in atmospheric parameter gradients in a specified region must be taken into account when interpreting radio occultation data. We show, that a correction functional can be developed using the refractivity index field calculated from the regional model in order to improve the radio occultation retrieval of atmospheric parameters. This functional is constructed from instantaneous model outputs, as well as from temporally averaged fields of refractivity using data of the HIRHAM4 model for the Arctic atmosphere. The correction functional derived from monthly averaged data reduced the retrieval errors of refractivity, temperature, and pressure in the troposphere, in particular, temperature retrieval errors are reduced up to 1 K. Application of this kind of functional depends on whether the model used for the construction of the functional is able to simulate the real mesoscale atmospheric structures. © 2004 Elsevier Ltd. All rights reserved.


Validation of water vapour profiles from GPS radio occultations in the Arctic

FIRST CHAMP MISSION RESULTS FOR GRAVITY, MAGNETIC AND ATMOSPHERIC STUDIES (2003) 441-446

M Gerding, A Weisheimer


Extratropical low-frequency variability in a three-level quasi-geostrophic atmospheric model with different spectral resolution

Journal of Geophysical Research D: Atmospheres 108 (2003)

A Weisheimer, MV Kurgansky, K Dethloff, D Handorf

Apart from variations of external forcing components and interactions between climate subsystems, natural atmospheric fluctuations with periods of years, decades and centuries can also be generated by inherent atmospheric dynamical instabilities of the flow. The objective of this study is to investigate the spatial and temporal structure of internal low-frequency atmospheric variability of the Northern Hemisphere using a minimum-complexity model of the extratropical circulation. Here, the main focus is the influence of varying spectral horizontal resolution on the formation of dominant patterns of variability. For this purpose, a three-level quasi-geostrophic atmospheric model with idealized thermal and orographic forcing has been integrated over 1,000 years under perpetual winter conditions with T5, T10, T15, and T21 resolutions. It has been shown that for the crude resolution T5 a rather strong bias occurs, whereas starting with T1O resolution, the nonlinear feedback between large- and small-scale features is reasonably well described. At this resolution a sort of plateau in the model performance has been reached, in respect to both the model climatology and the spatiotemporal structure of variability. Ultralow-frequency variability is most pronounced in the model's stratosphere and is associated with changes in the polar vortex strength and shape caused by vertically propagating planetary waves. Rossby wave trains in the lee of the model large-scale orography are the most dominant structures of long-period fluctuations in the middle troposphere. The results show that interannual- and decadal-scale variations can, in substantial part, be considered as a manifestation of the natural variability of the extratropical atmosphere. The inclusion of a seasonal cycle of the model's diabatic heating increases the interannual and interdecadal variability.


Predictability of weather and climate: From theory to practice - From days to decades

REALIZING TERACOMPUTING (2003) 1-18

TN Palmer


Forcing singular vectors and other sensitive model structures

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 129 (2003) 2401-2423

J Barkmeijer, T Iversen, TN Palmer


Benefits of increased resolution in the ECMWF ensemble system and comparison with poor-man's ensembles

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 129 (2003) 1269-1288

R Buizza, DS Richardson, TN Palmer


Potential improvement to forecasts of two severe storms using targeted observations

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 128 (2002) 1641-1670

M Leutbecher, J Barkmeijer, TN Palmer, AJ Thorpe


The economic value of ensemble forecasts as a tool for risk assessment: From days to decades

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 128 (2002) 747-774

TN Palmer


Predicting uncertainty in numerical weather forecasts

International Geophysics 83 (2002) 3-13

TN Palmer

The predictability of weather and climate forecasts is determined by the projection of uncertainties in both initial conditions and model formulation, onto flow-dependent instabilities of the chaotic climate attractor. Since it is essential to be able to estimate the impact of such uncertainties on forecast accuracy, no weather or climate prediction can be considered complete without a forecast of the associated flow-dependent predictability. The problem of predicting uncertainty can be posed in terms of the Liouville equation for the growth of initial uncertainty. However, in practice, the problem is approached using ensembles of integrations of comprehensive weather and climate prediction models, with explicit perturbations to both initial conditions and model formulation; the resulting ensemble of forecasts can be interpreted as a probabilistic prediction. Many of the difficulties in forecasting predictability arise from the large dimensionality of the climate system, and special techniques to generate ensemble perturbations have been developed. Methods to sample uncertainties in model formulation are also described. Practical ensemble prediction systems are described, and examples of resulting probabilistic weather forecast products shown. Methods to evaluate the skill of these probabilistic forecasts are outlined. By using ensemble forecasts as input to a simple decision-model analysis, it is shown that that probability forecasts of weather have greater potential economic value than corresponding single deterministic forecasts with uncertain accuracy. © 2002 Elsevier Inc. All rights reserved.


Potential improvement to forecasts of two severe storms using targeted observations

Quarterly Journal of the Royal Meteorological Society 128 (2002) 1641-1670

M Leutbecher, J Barkmeijer, TN Palmer, AJ Thorpe

The potential to improve short-range forecasts of two extratropical storms by using supplementary observations in regions lacking accurate observations is investigated. In the idealized framework used here, a control and a truth experiment are selected from a set of forecasts initialized with analyses from different numerical weather- prediction centres. Synthetic soundings of wind and temperature are created from the truth experiment and are assimilated with four-dimensional variational analysis using the operational observation-error estimates for radiosondes and the initial condition of the control experiment as background. Through multiple analysis/forecast experiments we obtain a nonlinear estimate of the optimal zone for observing (OZO): that is the zone in which the use of a given number of supplementary observations leads to the largest reduction in forecast error. We evaluate targeting techniques based on either total-energy singular vectors (TESVs) or on Hessian singular vectors (HSVs) by comparison with the OZO and by comparison with experiments in which the same amount of supplementary observations are distributed in an untargeted manner, namely with a random distribution scheme (RDS). Overall, the HSV targeting is superior to the TESV targeting in the two cases. In one case there is a significant difference between the target regions determined with TESVs and HSVs. The HSV-based observing strategy resembles the OZO in terms of the observing region and the achieved forecast-error reduction. With the RDS, the forecast error is variable and likely to be larger than the forecast error obtained with singular-vector targeting. Experiments with target regions of different sizes show that supplementary observations in an area of about 3 × 106 km2 are required to achieve a significant forecast improvement. A two-dimensional sampling pattern with soundings spaced at a distance of about 1-2 times the horizontal correlation length-scale of the background- error estimate appears very efficient. In additional impact experiments for one case, observations were perturbed with noise to represent observational error. The perturbations are almost as likely to improve the forecast as to worsen it compared with the forecast using unperturbed observations.

Pages