Short-Range and Medium-Range Weather Forecasting in the Extratropics during Wintertime with and without an Interactive Ocean

Abstract The ECMWF monthly forecasting system is used to investigate the impact that an interactive ocean has on short-range and medium-range weather predictions in the Northern Hemisphere extratropics during wintertime. On a hemispheric scale the predictive skill for mean sea level pressure (MSLP) with and without an interactive ocean is comparable. This can be explained by the relatively small impact that coupling has on MSLP forecasts. In fact, deterministic and ensemble integrations reveal that the magnitude of forecast error and the perturbation growth due to analysis uncertainties, respectively, by far outweigh MSLP differences between coupled and uncoupled integrations. Furthermore, no significant difference of the ensemble spread between the uncoupled and coupled system is found. The authors’ conclusions apply equally for a number of cases of rapidly intensifying extratropical cyclones in the North Atlantic region. Further experimentation with different atmospheric model versions, different horizontal atmospheric resolutions, and different ocean model formulation reveals the robustness of the findings. The results suggest that (for the cases, resolutions, and model complexities considered is this study) the benefit of using coupled atmosphere–ocean models to carry out 1–10-day MSLP forecasts is relatively small, at least in the Northern Hemisphere extratropics during wintertime.

Download Full-text

Impact of Coupling with an Ice–Ocean Model on Global Medium-Range NWP Forecast Skill

Monthly Weather Review ◽

10.1175/mwr-d-17-0157.1 ◽

2018 ◽

Vol 146 (4) ◽

pp. 1157-1180 ◽

Cited By ~ 19

Author(s):

Gregory C. Smith ◽

Jean-Marc Bélanger ◽

François Roy ◽

Pierre Pellerin ◽

Hal Ritchie ◽

...

Keyword(s):

Standard Deviation ◽

Large Scale ◽

Weather Forecasting ◽

Positive Impact ◽

Weather Prediction ◽

Ocean Model ◽

Forecast Skill ◽

Medium Range ◽

Forecasting System ◽

The Impact

The importance of coupling between the atmosphere and the ocean for forecasting on time scales of hours to weeks has been demonstrated for a range of physical processes. Here, the authors evaluate the impact of an interactive air–sea coupling between an operational global deterministic medium-range weather forecasting system and an ice–ocean forecasting system. This system was developed in the context of an experimental forecasting system that is now running operationally at the Canadian Centre for Meteorological and Environmental Prediction. The authors show that the most significant impact is found to be associated with a decreased cyclone intensification, with a reduction in the tropical cyclone false alarm ratio. This results in a 15% decrease in standard deviation errors in geopotential height fields for 120-h forecasts in areas of active cyclone development, with commensurate benefits for wind, temperature, and humidity fields. Whereas impacts on surface fields are found locally in the vicinity of cyclone activity, large-scale improvements in the mid-to-upper troposphere are found with positive global implications for forecast skill. Moreover, coupling is found to produce fairly constant reductions in standard deviation error growth for forecast days 1–7 of about 5% over the northern extratropics in July and August and 15% over the tropics in January and February. To the authors’ knowledge, this is the first time a statistically significant positive impact of coupling has been shown in an operational global medium-range deterministic numerical weather prediction framework.

Download Full-text

Seasonal-to-Decadal Predictability and Prediction of North American Climate—The Atlantic Influence

Journal of Climate ◽

10.1175/jcli3942.1 ◽

2006 ◽

Vol 19 (23) ◽

pp. 6005-6024 ◽

Cited By ~ 17

Author(s):

H. M. Van den Dool ◽

Peitao Peng ◽

Åke Johansson ◽

Muthuvel Chelliah ◽

Amir Shabbar ◽

...

Keyword(s):

North American ◽

Seasonal Prediction ◽

Atmospheric Model ◽

The United States ◽

Seasonal Forecast ◽

Ocean Model ◽

Prediction Skill ◽

Basic Material ◽

Atlantic Sector ◽

The Impact

Abstract The question of the impact of the Atlantic on North American (NA) seasonal prediction skill and predictability is examined. Basic material is collected from the literature, a review of seasonal forecast procedures in Canada and the United States, and some fresh calculations using the NCEP–NCAR reanalysis data. The general impression is one of low predictability (due to the Atlantic) for seasonal mean surface temperature and precipitation over NA. Predictability may be slightly better in the Caribbean and the (sub)tropical Americas, even for precipitation. The NAO is widely seen as an agent making the Atlantic influence felt in NA. While the NAO is well established in most months, its prediction skill is limited. Year-round evidence for an equatorially displaced version of the NAO (named ED_NAO) carrying a good fraction of the variance is also found. In general the predictability from the Pacific is thought to dominate over that from the Atlantic sector, which explains the minimal number of reported Atmospheric Model Intercomparison Project (AMIP) runs that explore Atlantic-only impacts. Caveats are noted as to the question of the influence of a single predictor in a nonlinear environment with many predictors. Skill of a new one-tier global coupled atmosphere–ocean model system at NCEP is reviewed; limited skill is found in midlatitudes and there is modest predictability to look forward to. There are several signs of enthusiasm in the community about using “trends” (low-frequency variations): (a) seasonal forecast tools include persistence of last 10 years’ averaged anomaly (relative to the official 30-yr climatology), (b) hurricane forecasts are based largely on recognizing a global multidecadal mode (which is similar to an Atlantic trend mode in SST), and (c) two recent papers, one empirical and one modeling, giving equal roles to the (North) Pacific and Atlantic in “explaining” variations in drought frequency over NA on a 20 yr or longer time scale during the twentieth century.

Download Full-text

Origin and Impact of Initialization Shocks in Coupled Atmosphere–Ocean Forecasts*

Monthly Weather Review ◽

10.1175/mwr-d-15-0076.1 ◽

2015 ◽

Vol 143 (11) ◽

pp. 4631-4644 ◽

Cited By ~ 41

Author(s):

David P. Mulholland ◽

Patrick Laloyaux ◽

Keith Haines ◽

Magdalena Alonso Balmaseda

Keyword(s):

Data Assimilation ◽

Coupled System ◽

Atmospheric Temperature ◽

Ocean Model ◽

Forecast Skill ◽

Weather Forecasts ◽

Model Component ◽

Medium Range ◽

Series Of Experiments ◽

Coupled Data Assimilation

Abstract Current methods for initializing coupled atmosphere–ocean forecasts often rely on the use of separate atmosphere and ocean analyses, the combination of which can leave the coupled system imbalanced at the beginning of the forecast, potentially accelerating the development of errors. Using a series of experiments with the European Centre for Medium-Range Weather Forecasts coupled system, the magnitude and extent of these so-called initialization shocks is quantified, and their impact on forecast skill measured. It is found that forecasts initialized by separate oceanic and atmospheric analyses do exhibit initialization shocks in lower atmospheric temperature, when compared to forecasts initialized using a coupled data assimilation method. These shocks result in as much as a doubling of root-mean-square error on the first day of the forecast in some regions, and in increases that are sustained for the duration of the 10-day forecasts performed here. However, the impacts of this choice of initialization on forecast skill, assessed using independent datasets, were found to be negligible, at least over the limited period studied. Larger initialization shocks are found to follow a change in either the atmosphere or ocean model component between the analysis and forecast phases: changes in the ocean component can lead to sea surface temperature shocks of more than 0.5 K in some equatorial regions during the first day of the forecast. Implications for the development of coupled forecast systems, particularly with respect to coupled data assimilation methods, are discussed.

Download Full-text

Three-dimensional visualization of ensemble weather forecasts – Part 1: The visualization tool Met.3D (version 1.0)

Geoscientific Model Development ◽

10.5194/gmd-8-2329-2015 ◽

2015 ◽

Vol 8 (7) ◽

pp. 2329-2353 ◽

Cited By ~ 17

Author(s):

M. Rautenhaus ◽

M. Kern ◽

A. Schäfler ◽

R. Westermann

Keyword(s):

Visual Analysis ◽

Weather Forecasting ◽

Spatial Perception ◽

Three Dimensional ◽

Atmospheric Model ◽

Weather Forecasts ◽

Research And Teaching ◽

Grid Topology ◽

Ensemble Visualization ◽

The Impact

Abstract. We present "Met.3D", a new open-source tool for the interactive three-dimensional (3-D) visualization of numerical ensemble weather predictions. The tool has been developed to support weather forecasting during aircraft-based atmospheric field campaigns; however, it is applicable to further forecasting, research and teaching activities. Our work approaches challenging topics related to the visual analysis of numerical atmospheric model output – 3-D visualization, ensemble visualization and how both can be used in a meaningful way suited to weather forecasting. Met.3D builds a bridge from proven 2-D visualization methods commonly used in meteorology to 3-D visualization by combining both visualization types in a 3-D context. We address the issue of spatial perception in the 3-D view and present approaches to using the ensemble to allow the user to assess forecast uncertainty. Interactivity is key to our approach. Met.3D uses modern graphics technology to achieve interactive visualization on standard consumer hardware. The tool supports forecast data from the European Centre for Medium Range Weather Forecasts (ECMWF) and can operate directly on ECMWF hybrid sigma-pressure level grids. We describe the employed visualization algorithms, and analyse the impact of the ECMWF grid topology on computing 3-D ensemble statistical quantities. Our techniques are demonstrated with examples from the T-NAWDEX-Falcon 2012 (THORPEX – North Atlantic Waveguide and Downstream Impact Experiment) campaign.

Download Full-text

Including Uncertainties of Sea Surface Temperature in an Ensemble Kalman Filter: A Case Study of Typhoon Sinlaku (2008)

Weather and Forecasting ◽

10.1175/waf-d-11-00136.1 ◽

2012 ◽

Vol 27 (6) ◽

pp. 1586-1597 ◽

Cited By ~ 16

Author(s):

Masaru Kunii ◽

Takemasa Miyoshi

Keyword(s):

Kalman Filter ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Ensemble Kalman Filter ◽

Forecast Error ◽

Ocean Model ◽

Sea Surface ◽

Ensemble Spread ◽

Error Covariance ◽

The Impact

Abstract Sea surface temperature (SST) plays an important role in tropical cyclone (TC) life cycle evolution, but often the uncertainties in SST estimates are not considered in the ensemble Kalman filter (EnKF). The lack of uncertainties in SST generally results in the lack of ensemble spread in the atmospheric states near the sea surface, particularly for temperature and moisture. In this study, the uncertainties of SST are included by adding ensemble perturbations to the SST field, and the impact of the SST perturbations is investigated using the local ensemble transform Kalman filter (LETKF) with the Weather Research and Forecasting Model (WRF) in the case of Typhoon Sinlaku (2008). In addition to the experiment with the perturbed SST, another experiment with manually inflated ensemble perturbations near the sea surface is performed for comparison. The results indicate that the SST perturbations within EnKF generally improve analyses and their subsequent forecasts, although manually inflating the ensemble spread instead of perturbing SST does not help. Investigations of the ensemble-based forecast error covariance indicate larger scales for low-level temperature and moisture from the SST perturbations, although manual inflation of ensemble spread does not produce such structural effects on the forecast error covariance. This study suggests the importance of considering SST perturbations within ensemble-based data assimilation and promotes further studies with more sophisticated methods of perturbing SST fields such as using a fully coupled atmosphere–ocean model.

Download Full-text

Modeling ocean response to an extreme Bora event in Northern Adriatic using one-way and two-way atmosphere-ocean coupling

Ocean Science Discussions ◽

10.5194/osd-12-1389-2015 ◽

2015 ◽

Vol 12 (4) ◽

pp. 1389-1431

Author(s):

M. Ličer ◽

P. Smerkol ◽

A. Fettich ◽

M. Ravdas ◽

A. Papapostolou ◽

...

Keyword(s):

Seawater Temperature ◽

Coupled System ◽

Atmospheric Model ◽

Ocean Model ◽

Ocean Modeling ◽

Northern Adriatic ◽

Ocean Response ◽

Ocean Coupling ◽

The One

Abstract. We study the performances of (a) fully two-way coupled atmosphere–ocean modeling system and (b) one-way coupled ocean model (forced by the atmospheric model hourly output), as compared to the available in situ (mooring and CTD) measurements during and after an strong Bora wind event in February 2012, which led to extreme air–sea interactions and record breaking seawater cooling and dense water formation in Northern Adriatic. The simulations span the period between January and March 2012. The models used were ALADIN (4.4 km resolution) on the atmospheric side and Adriatic setup of POM (1°/30 × 1°/30 angular resolution) on the ocean side. The atmosphere–ocean coupling was implemented using the OASIS3-MCT model coupling toolkit. We show, using in situ seawater temperature measurements, that the two-way atmosphere–ocean coupling improves the ocean response to Bora because it captures transient Bora-induced cooling better than the one-way coupled version of the ocean model. We show that this difference stems mainly from an underestimation of air–sea temperature difference in one-way coupled system during the Bora episode, leading to an underestimation of sensible heat losses from the ocean in the one-way coupled system. We show these losses exhibit significant impact on baroclinic circulation on synoptic timescales. We use CTD observations in the Gulf of Trieste to show that when compared to the one-way setup, the two-way coupled system produces a similar estimation of salinities and density anomalies before the Bora episode, but a significantly better estimation of these quantities afterwards.

Download Full-text

Dynamic downscaling of the ERA-40 data using a mesoscale meteorological model

Mediterranean Marine Science ◽

10.12681/mms.59 ◽

2011 ◽

Vol 12 (1) ◽

pp. 183 ◽

Cited By ~ 5

Author(s):

A. PAPADOPOULOS ◽

G. KORRES ◽

P. KATSAFADOS ◽

D. BALLAS ◽

L. PERIVOLIOTIS ◽

...

Keyword(s):

Dynamical Downscaling ◽

Weather Forecasting ◽

Quantitative Estimation ◽

Three Dimensional ◽

Atmospheric Model ◽

Hydrological Models ◽

Atmospheric Conditions ◽

Meteorological Model ◽

Medium Range ◽

Forecasting System

A sophisticated downscaling procedure that was applied to reproduce high resolution historical records of the atmospheric conditions across the Mediterranean region is presented in this paper. This was accomplished by the dynamical downscaling of the European Center for Medium-Range Forecasts ERA-40 reanalyses with the aid of the atmospheric model of the POSEIDON weather forecasting system. The full three dimensional atmospheric fields with 6 hours of temporal resolution and the surface meteorological parameters at hourly intervals were produced for a 10-year period (1995-2004). The meteorological variables are readily available at 10 km resolution and may constitute the atmospheric forcing to drive wave, ocean hydrodynamic and hydrological models, as well as the baseline data for environmental impact assessment studies. A brief overview of the procedure and a quantitative estimation of the benefit of the new dynamical downscaling dataset are presented.

Download Full-text

Wave–current interactions in a wind-jet region

Ocean Science ◽

10.5194/os-15-1-2019 ◽

2019 ◽

Vol 15 (1) ◽

pp. 1-20 ◽

Cited By ~ 2

Author(s):

Laura Ràfols ◽

Manel Grifoll ◽

Manuel Espino

Keyword(s):

Numerical Models ◽

Mixed Layer Depth ◽

Coupled System ◽

Ocean Model ◽

Water Current ◽

Northern Margin ◽

Water Column Stratification ◽

Regional Ocean Model System ◽

Current Flows ◽

The Impact

Abstract. Wave–current interactions (WCIs) are investigated. The study area is located at the northern margin of the Ebro shelf (northwestern Mediterranean Sea), where episodes of strong cross-shelf wind (wind jets) occur. The aim of this study is to validate the implemented coupled system and investigate the impact of WCIs on the hydrodynamics of a wind-jet region. The Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) modeling system, which uses the Regional Ocean Model System (ROMS) and Simulating WAves Nearshore (SWAN) models, is used in a high-resolution domain (350 m). Results from uncoupled numerical models are compared with a two-way coupling simulation. The results do not show substantial differences in the water current field between the coupled and the uncoupled runs. The main effect observed when the models are coupled is in the water column stratification, due to the turbulent kinetic energy injection and the enhanced surface stress, leading to a larger mixed-layer depth. Regarding the effects on the wave fields, the comparison between the coupled and the uncoupled runs shows that, when the models are coupled, the agreement of the modeled wave period significantly improves and the wave energy (and thus the significant wave height) decreases when the current flows in the same direction as the waves propagate.

Download Full-text

Internal Model Variability of the Regional Coupled System Model GCOAST-AHOI

Atmosphere ◽

10.3390/atmos11030227 ◽

2020 ◽

Vol 11 (3) ◽

pp. 227 ◽

Cited By ~ 3

Author(s):

Ha Thi Minh Ho-Hagemann ◽

Stefan Hagemann ◽

Sebastian Grayek ◽

Ronny Petrik ◽

Burkhardt Rockel ◽

...

Keyword(s):

Internal Model ◽

Climate Model ◽

Extreme Event ◽

Regional Climate ◽

Coupled System ◽

Internal Variability ◽

Atmospheric Model ◽

Ocean Model ◽

System Model ◽

Model Variability

Simulations of a Regional Climate Model (RCM) driven by identical lateral boundary conditions but initialized at different times exhibit the phenomenon of so-called internal model variability (or in short, Internal Variability—IV), which is defined as the inter-member spread between members in an ensemble of simulations. Our study investigates the effects of air-sea coupling on IV of the regional atmospheric model COSMO-CLM (CCLM) of the new regional coupled system model GCOAST-AHOI (Geesthacht Coupled cOAstal model SysTem: Atmosphere, Hydrology, Ocean and Sea Ice). We specifically address physical processes parameterized in CCLM, which may cause a large IV during an extreme event, and where this IV is affected by the air-sea coupling. Two six-member ensemble simulations were conducted with GCOAST-AHOI and the stand-alone CCLM (CCLM_ctr) for a period of 1 September–31 December 2013 over Europe. IV is expressed by spreads within the two sets of ensembles. Analyses focus on specific events during this period, especially on the storm Christian occurring from 27 to 29 October 2013 in northern Europe. Results show that simulations of CCLM_ctr vary largely amongst ensemble members during the storm. By analyzing two members of CCLM_ctr with opposite behaviors, we found that the large uncertainty in CCLM_ctr is caused by a combination of two factors (1) uncertainty in parameterization of cloud-radiation interaction in the atmospheric model. and (2) lack of an active two-way air-sea interaction. When CCLM is two-way coupled with the ocean model, the ensemble means of GCOAST-AHOI and CCLM_ctr are relatively similar, but the spread is reduced remarkably in GCOAST-AHOI, not only over the ocean where the coupling is done but also over land due to the land-sea interactions.

Download Full-text