June 2004 - Workshop 7
The Seventh AOMIP Workshop (June 14-15), was held at the Geophysical Fluid Dynamics Laboratory (GFDL) in Princeton, NJ, and was timed to precede the CLIVAR Workshop: "Evaluating the Ocean Component of IPCC-Class Models" (June 16-18). Details about the workshop, including downloadable versions of meeting presentations, are available at the AOMIP website.
The AOMIP workshop was coordinated with the CLIVAR workshop in order for AOMIP participants to meet directly with key representatives of the global-ocean modeling community, that are striving to develop the Ocean Model Intercomparison Project (OMIP), which is in some respects analogous to AOMIP, but with a focus on the global ocean. Participants of both workshops met jointly to discuss questions of mutual interest, such as forcing data sets and project organization. The AOMIP intention is to work with OMIP to produce a better representation of arctic processes, and of arctic - global-ocean interaction, in global-ocean models. Ultimately, this collaboration provides a pathway for AOMIP science results to feed into and impact IPCC science.
Day 1 (June 14th) of the workshop involved a comprehensive discussion of results from the "Coordinated Analysis: 1948-2004" experiment. In total, 21 talks from 14 institutions presented results and analysis of AOMIP model runs from this experiment.
Interwoven among the talks, many topics were thoroughly discussed throughout the day, mostly motivated by the interesting scientific results presented. The key topics were:
- Propagation and transformation of Atlantic-Layer Water (ALW) in the Arctic Ocean;
- Variability of the Arctic Ocean freshwater content;
- Role of tides in the Arctic Ocean and in sea-ice dynamics and thermodynamics;
- Restoring and non-restoring alternatives;
- Arctic climate variability in global and regional models;
- General, model intercomparison issues;
- AOMIP organization, goals and objectives.
Day 2 (June 15) was dedicated to a discussion of other topics, including model calibration and validation approach; model improvement plan; collaboration and coordination of AOMIP activity with other MIPs (with a particular emphasis on OMIP in this workshop); and project-logistic questions, such as ongoing coordination, funding opportunities, research themes, and publications.
The workshop conclusions and recommendations are:
- AOMIP's working plan for the next 3 years (March 1, 2004, to February 28, 2007) includes: completion of coordinated set of 50- and 100-year simulations; intercomparison of model outputs; identification of key differences; determination of causes of differences among models; and model improvements.
- The final AOMIP activity will be an analysis of Arctic-Ocean variability over a 100-year time scale and to make recommendations to the global-ocean modeling community on Arctic-Ocean modeling.
- There are striking differences in the circulation of ALW and its transformations among AOMIP models. Approximately half of the models show cyclonic circulation of Atlantic water and the other half show the opposite circulation. It is extremely important to identify the physical mechanism underlying these differences. It is equally important to validate the models based on observational data.
- The nature and relevance of the ALW circulation is largely not appreciated by the global climate modeling community. AOMIP is fostering an awareness of this issue by holding joint meetings with global ocean and global climate modelers.
- There is an urgent need for more observational data on the ALW. AOMIP is performing 50 and 100 year simulations, and thus we are especially interested in an historical perspective on ALW characteristics . Such data sets are currently collected at IARC as part of NABOS and similar projects concerning low-frequency climate variability. As a first, concrete step in integration efforts between AOMIP and NABOS, AOMIP requests from NABOS all historical data characterizing water temperature and salinity; circulation parameters including currents at different levels; depths of the upper and bottom boundaries of ALW; integrated characteristics such as heat and salt content; and fluxes of ALW through different sections. Such data can be used by AOMIP for model validation, calibration, and finally, improvement.
- The AOMIP, in turn, based on numerical experiments, can provide NABOS with recommendations about the most representative locations for ALW monitoring.
- In order to further integrate AOMIP and NABOS, we recognize the need for a 2005 AGU special session, followed by a workshop specifically dedicated to the ALW circulation and transformation.
- There are striking differences in the Arctic Ocean freshwater content and its seasonal, interannual, and decadal variability among different AOMIP-regional and AOMIP-global models. Variability of the freshwater content, and mechanisms of fresh water accumulation and release, is extremely important for understanding major issues relating to global-ocean meridional overturning circulation and climate change. Workshop participants recognized several important deficiencies in the current understanding of the problems of fresh water simulations. These problems include uncertainties in the choices of boundary conditions for rivers, straits, and open boundaries (volume, diffusion or precipitation inflows/outflows); restoring or not restoring alternatives; and forcing data (rates of precipitation/evaporation and river runoff). For example, existing models use seasonal climatology for precipitation, which a priori contradicts the basic assumption of climate change, and leads to an imbalance in fresh water inputs and outputs. As a result, practically all regional models (without restoring) have significant salinity drifts. Additional observational data collection and interpretation, for the specific purpose of ocean and climate modeling in the Arctic, is needed.
- AOMIP researchers have already proposed several improvements for Arctic models, including implementation of tidal dynamics into ocean and ice models. Preliminary experiments have shown that tidal and inertial sea-ice motion leads to additional generation of sea-ice mass and a redistribution of sea-ice deformations and fracture-zone formations. Inclusion of tidal dynamics into the ocean component of coupled models could improve mixing and heat transformations in the ocean and help better understand the heat release mechanism from the ALW to the bottom of sea ice and into the lower atmosphere. Preliminary experiments have shown that this mechanism is responsible for sea-ice thinning in the regions with high level of tidal energy dissipation.
- Another direction of improvements is an inclusion of processes responsible for establishing and breaking of the landfast ice. In the existing models regions of landfast ice are treated as pack ice, which drifts. As a consequence, more momentum is transferred to the ocean from wind stresses than in the real ocean. Absence of landfast ice in the models means an improper representation of coastal polynyas, of sea-ice production, and possibly of deep-water production. This is because some of these processes occur along the coastline in the models, instead of along the continental, shelf break as in the real ocean.
- The important objectives for practically all of the AOMIP researchers for the immediate future are: " Complete the "coordinated-analysis: 1948-2004" experiment; " Interpolate all requested model data to the AOMIP common grid; " Upload all requested model data to the AOMIP Live Access Server (LAS) at NYU; " Start model intercomparison procedure according to the AOMIP protocol of coordinated and distributed tasks (see AOMIP web site for details). (target, starting date for this activity is September 1, 2004). " Prepare publications for AOMIP special journal volume. (target date for papers to be submitted is March 1, 2005).
- The AOMIP workshop participants recognize the importance of model validation, calibration, and improvement. In order to facilitate the carrying out of such work, it is necessary to prepare standard model validation data sets, which include observational data organized for specific AOMIP tasks. AOMIP researchers agreed to prepare and distribute among AOMIP investigators the necessary data. The data will be posted at the AOMIP web site, and thus available to the entire modeling community. It is important to complete this work by December 1, 2004, in order to start model validation and to obtain results by February 2005. The data sets, with instructions on how to use these data for validation procedures, are:
- LW temperature, salinity, and circulation (with a focus on ALW circulation and transformation, it is extremely important to have these data sets). AOMIP requests this information from NABOS and hopes to have wider discussions with IARC scientists. (Karcher, Steele)
- Radioactive tracer data (iodine, cesium) exist from 1980's (Karcher).
- Sea-ice drift and sea-ice deformation (Hibler).
- Sea-ice extent and concentration based on passive microwave data (Zhang).
- Monthly sea level at the most representative tide gauge stations (Proshutinsky).
- Sea-ice thickness from submarines (Hunke) and ULS (Johnson).
- Long-term T and S time series from hydrographic sections (Kola Section, Faroe-Shetland Section, Fram Strait, SCICEX, etc. (Steele).
- Current meter data from all possible moorings (All, based on institutional sources).
- Long-term data sets from ASOF (Karcher)
- Collaboration with other MIPs, especially ARCMIP and OMIP, is an important activity of the AOMIP project. During the AOMIP and OMIP workshops, both projects exchanged information about project goals, objectives, problems, and possible solutions. It was reported that OMIP forcing data set does not well represent arctic conditions, which could lead to unrealistic sea-ice thickness and concentration. Inappropriate forcing data could influence the simulation by global models of variability of water circulation, heat content, freshwater content, and rate of overturning circulation. Participants agreed that E. Hunke and R. Gerdes will serve to coordinate information, between the AOMIP and OMIP communities, about such problems as well as accomplishments.
- Internal AOMIP issues were discussed at the end of workshop and focused on publication needs and data archiving procedures. The main difficulty relates to the interruption of support for an AOMIP postdoc position at NYU. After thorough discussions of both problems, AOMIP recommends:
- Each AOMIP team/scientist will prepare a paper for joint AOMIP publication by March 1, 2005. These publications will be submitted to JGR or Deep Sea Research, part 2. Papers should be dedicated to AOMIP intercomparison of model-model and model-data results for different environmental parameters; model validation and calibration; and interpretation of the Arctic Ocean changes based on model results and observations.
- Organize a poster session at Bjerknes Centennial Conference in Bergen, September 3-5, 2004, and to submit 11 poster presentations, which will be presented by G. Holloway, K. Koeberle, E. Golubeva, and M. Karcher. The posters will also be downloadable from the AOMIP web site at URL http://fish.cims.nyu.edu/project_aomip/publications/bjerkness_2004.html.
- Represent AOMIP at Arctic Regional Climate Model Intercomparison Project (ARCMIP) in December (Melbourne, Australia) and to coordinate inter-project activities and to plan future collaboration with coupled atmosphere-ice-ocean numerical experiments. G. Holloway, D. Holland, W. Maslowski, and A. Proshutinsky plan to represent AOMIP at the ARCMIP meeting.
- For a closer link of AOMIP with ASOF M. Karcher will present AOMIP project status at the next ASOF-ISSG meeting (Vigo, Spain) in October, 2004.
- AOMIP requests additional funds from IARC to support the salary of a Research Associate at the New York University. Based on past experience in operating the NYU LAS, the amount of support requested is 5 months per year of a Research Associate. The major responsibilities of the LAS-support-person will be: 1) updating the LAS system; 2) providing efficient communication and data exchange among AOMIP teams; 3) preparing model (and observational) data for the LAS, 4) interpolating, plotting, and extracting data for AOMIP teams, following the AOMIP protocol; and 5) solving non-standard data-exchange problems, for example, an analysis of very high-resolution model data, or a particular type of data analysis not currently defined in the AOMIP protocol.