About the NCEP MMAB Global Superstructure Ice Accretion Guidance
revised April 2, 2004; reviewed July 3, 2013
INTRODUCTIONFor marine purposes ice accretion may be defined as the accumulation of ice formed on 1) exposed structural components of ships or 2) structures above the water surface either on the coast or at sea.
The importance of advising marine interests of the existence and expected location and intensity of ice accretion is two fold.
1. Safety. The accumulation of ice on small vessells has the potential of causing serious handling problems leading to instability and capsizing. This is particularly true of fishing trawlers which may have tons of fish and water shifting about in their holds. The extra weight of ice on masts and rigging not only makes the vessel top heavy, but also increases its "sail area" and hence the adverse affect the wind has on it. This causes difficulties in handling the vessel. While larger ships have less of a problem with ice induced instability, the accumulation of ice on antennae makes radio communication difficult, if not impossible, and impedes the effectiveness of radar. On all sizes of vessels ice accumulation presents a serious safety hazard to all working on deck.
2. Efficiency. During fishing operations the ability to work deck equipment unhampered is of prime importance. Ice accretion, of course, hinders the efficient use of deck equipment and slows the work. Larger vessels particlarly container ships may find that, upon reaching port, the deck cargo is ice encrusted to the extent that unloading of cargo is impossible even though the vessel is safely berthed.
Heretofore, the output of the system was available only as a part of the Marine Significant Weather Chart with a 65 x 65 grid point resolution for the northern hemisphere and as a facsimile product for the Alaska Region. As a part of the conversion from IBM based to UNIX based computer systems, a number of changes to the superstructure ice accretion system were introduced. The most important was an increase in resolution to a 1 x 1 degree grid.
This version expands the product to be global in extent, utilizes the 2 m air temperature and 10 m winds from the GFS and the RTG_SST in place of the Reynolds' SST.
DEVELOPMENTThe NCEP Superstructure Ice Accretion Forecast System was developed with the use of a statistical procedure developed by Overland et al. (1986) at the Pacific Marine Environmental Research Laboratory of NOAA at Seattle, Washington. This procedure relates icing rates to meteorological and physical parameters. These are wind speed, freezing point of sea water, air temperature and sea surface temperature. The method was developed for trawlers in the 20 to 75 meter length range, underway at normal speeds in open seas, and not heading downwind.
AVAILABILITYIce accretion is depicted in the NAWIPS system for the National Centers and eventually on AWIPS and GTS. Ice accretion is depicted via these means the year-round for projections from 00 to 168 hours at 3 hour intervals on the 0000, 0600, 1200, and 1800 UTC cycles on NAWIPS.
We continue to keep it on Internet for general use and comment. The global 1x1 deg is also available in GRIB and gif images for ftp purposes.
Send comments or questions to Robert.Grumbine@noaa.gov
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