Papers by Robert Grumbine
As part of the Pelagic Ross Ice Shelf Measurement project, 29 current meters were deployed in the... more As part of the Pelagic Ross Ice Shelf Measurement project, 29 current meters were deployed in the Ross Sea near the ice-shelf edge during the 1983 and 1984 field seasons. The data from these meters give current speed and direction every hour for over a year in most locations. These data should reveal the characteristics of Ross Sea ocean circulation and indicate which processes are most important in ventilating the cavity below the Ross Ice Shelf. One way to analyze these data is to identify periodicity in the currents and thereby to obtain a characteristic fingerprint of ocean dynamics. If the periods in the currents are found to be the same as tidal or season, for example, then the currents are probably caused by tidal or seasonal forcing. To identify such periodicity, a method is needed to discriminate between natural periodicities and apparent periodicities caused by measurement error and random fluctuations. The author used the deviation of current amplitude from the estimated trend to judge the significance of the period tested. He also required that a given periodicity be considered significant on several (at least three) of the current meters before concluding that it was probably physical. Although this method for identifying periods was developed for velocity analysis, it will work for other times series, such as temperature. Results are given.
Bulletin of the American Meteorological Society, Mar 1, 2023
What: One hundred eighty-seven scientists, stakeholders, and representatives from operational for... more What: One hundred eighty-seven scientists, stakeholders, and representatives from operational forecasting centers and international bodies assembled in person and online to review the accomplishments and impacts of YOPP and make recommendations on prediction-related priorities for future international polar research projects.
Ocean Modelling, Sep 1, 2019
A depth-integrated high resolution (down to 25-50 m) tide and storm surge model has been develope... more A depth-integrated high resolution (down to 25-50 m) tide and storm surge model has been developed for the Alaska region with a focus on the coasts of western Alaska. The model uses the ADCIRC basin-to-channel scale unstructured grid circulation code forced with Climate Forecast System version 2 reanalysis meteorology. The tidal solution has been validated at 121 shelf and nearshore stations, with lower overall errors than a data assimilated tidal model (FES2012). The ADCIRC model shows considerable skill at simulating tide and coastal surge, and resulting overland flooding on the Yukon-Kuskokwim Delta, during both summer and winter storms. The root-mean-square-error of the model does not exceed 20 cm at any station, outperforming the Global Ocean Forecasting System (GOFS 3.1), a 1/12 • data assimilated ocean general circulation model which is coupled to sea ice physics. The ADCIRC model incorporates the effect of sea ice through parameterizations of the wind drag coefficient, modifying the air-sea momentum transfer under ice coverage. Three large winter storms with distinctly different ice coverages along the coasts of western Alaska were chosen to exhibit the variable effect of sea ice on the resulting storm surge. Under forming coastal ice coverage, local increases in water levels due to ice is seen in coastal areas, and under predominantly dense pack ice, an increase in momentum transfer in the marginal sea ice at the shelf break leads to an increase in sea levels across the entire Bering Sea, both commensurate with observations. Under the most variable ice fields, results are mixed, in part due to uncertainties in the air-sea-ice drag parameterization such as related to the assumption that sea ice drift and wind velocities are always well correlated. Including a description of sea ice drift and current speeds explicitly in the air-sea-ice drag formulation and considering wave-surge-ice interaction should improve the description of momentum transferred to the water column and resulting simulation of surge.
Weather and Forecasting, Dec 1, 1999
The surface energy budget in Antarctic latitudes is evaluated for the medium-range numerical weat... more The surface energy budget in Antarctic latitudes is evaluated for the medium-range numerical weather forecasts produced by the National Centers for Environmental Prediction (NCEP) and for the NCEP-National Center for Atmospheric Research reanalysis project during the winter, spring, and summer special observing periods (SOPs) of the Antarctic First Regional Observing Study of Troposphere project. A significant change in the energy balance resulted from an extensive model update beginning with the forecasts initialized on 11 January 1995 during the summer SOP. Both the forecasts and the reanalysis include significant errors in the surface energy balance over Antarctica. The errors often tend to cancel and thus produce reasonable surface temperature fields. General errors include downward longwave radiation about 30-50 W m Ϫ2 too small. Lower than observed cloudiness contributes to this error and to excessive downward shortwave radiation at the surface. The model albedo over Antarctica, about 75%, is lower than that derived from observations, about 81%. During the polar day, errors in net longwave and net shortwave radiation tend to cancel. The energy balance over Antarctica in the reanalysis is, in general, degraded from that of the forecasts. Seasonal characteristics of the surface energy balance include cooling over East Antarctica and slight warming over West Antarctica during NCEP forecasts for the winter SOP. Wintertime surface warming by downward sensible heat flux is larger than observations by 21-36 W m Ϫ2 and tends to balance the excessive longwave cooling at the surface. During the spring SOP, forecast sensible heat flux produces an excessive heating contribution by about 20 W m Ϫ2. Latent heat flux during the Antarctic winter for the reanalysis is at least an order of magnitude larger than the very small observed values.
Journal of Geophysical Research, Jun 1, 1997
Available rawinsonde, automatic weather station (AWS), ship, and synthesized long-term observatio... more Available rawinsonde, automatic weather station (AWS), ship, and synthesized long-term observations are used to evaluate the Antarctic numerical analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the U.S. National Centers for Environmental Prediction (NCEP) from 1985 to 1994. Twice-daily variations in the ECMWF surface pressure analyses compare closely with AWS units of the U.S. Antarctic Program and ship observations. The NCEP analyses over the same period show substantial improvement, particularly during the period 1985-1990. Surface air temperatures and winds do not agree so closely, which may result from analyses error, the localized nature of the fields, or a combination. Validation of the analyses standard pressure level fields using available rawinsonde data reveal a general long-term decrease in RMS errors with time for both analyses. RMS errors in NCEP 200 hPa geopotential heights of over 200 geopotential meters (gpm) for central plateau stations are evident only prior to May 1986. However, a significant upward trend from 1989 to 1993 in geopotential height RMS differences is apparent at several levels. The ECMWF analyses are generally found to be superior and offer a reasonable depiction of the broadscale atmospheric circulation; however, deficiencies in midtropospheric temperatures and lower tropospheric winds are evident. Comparisons of ship data from individual cruises of the S.A. Agulhas and the R/V Nathaniel B. Palmer to the numerical analyses reveal substantial agreement for pressure and temperature variables. Observations from the Nathaniel B. Palmer in the Amundsen and Bellingshausen Seas were not available to the weather forecasting centers. Results presented here indicate that a large amount of the available data is being incorporated and that large deficiencies identified in previous studies are being addressed, although areas of concern remain. Deficiencies in comparisons to specific stations are common to both analyses, implying continued communications problems. In particular, grid values corresponding to individual stations including the now-closed Leningradskaya base and Mirnyy are found to be conspicuously deficient at the 200 hPa level for both analyses.
6th Conference on Polar Meteorlogy and Oceanography and the 11th Conference on Interaction of the Sea and Atmosphere, May 17, 2001
Weather and Forecasting, Sep 1, 1994
Weather and Forecasting, Dec 1, 1999
Analyses and medium-range numerical weather forecasts produced by the National Centers for Enviro... more Analyses and medium-range numerical weather forecasts produced by the National Centers for Environmental Prediction are evaluated poleward of 50ЊS during the July 1994 special observing period of the Antarctic First Regional Observing Study of the Troposphere project. Over the Antarctic plateau, the poor representation of the continent's terrain creates ambiguity in assessing the quality of surface variables. An examination of the vertical temperature profile, however, finds the near-surface temperature inversion strength to be substantially smaller than the observed climatology at the zero forecast hour. This arises from surface temperatures that are warmer than expected. Significant adjustment occurs in a variety of fields over the first few days of the mediumrange forecast, which likely results from the initial hour's suspect temperature profile. A spatially oscillating series of forecast anomalies in the zonally averaged temperature cross section stretches to middle latitudes by day 3. Near-surface and upper-troposphere values are found actually to improve at the South Pole with forecast time, although some fields continue to adjust through day 7. Although the examination presented here does not give a complete diagnosis, differences between observations and analyses suggest deficiencies with the model initial fields have a major role in producing the substantial model drift found. Atmospheric moisture over the continental interior does not change significantly with forecast hour, although the distinct contrast between nearshore and interior conditions lessens with forecast time. A spurious high-latitude wave pattern is found for a variety of variables. The pattern of this distortion remains constant with forecast hour. Over the ocean, large forecast pressure and height differences with analyses are associated with blocking conditions. However, it is unclear whether this results from deficiencies in the forecast model or the meager observational network over the Southern Ocean.
Annals of Glaciology, 1990
Weather and Forecasting, Sep 1, 1998
Both sea ice forecast models and methods to measure their skill are needed for operational sea ic... more Both sea ice forecast models and methods to measure their skill are needed for operational sea ice forecasting. Two simple sea ice models are described and tested here. Four different measures of skill are also tested. The forecasts from the newer sea ice model are found to perform better, regardless of the skill measure used. All four skill measures show essentially the same behavior, in terms of having no dependence on season and being roughly constant. All four measures also agree that there is no decline in skill with time through the 6-day period of forecast. * OMB Contribution Number 114.
Bulletin of the American Meteorological Society, Feb 1, 1998
Arctic air masses have direct impacts on the weather and climatic extremes of midlatitude areas s... more Arctic air masses have direct impacts on the weather and climatic extremes of midlatitude areas such as central North America. Arctic physical processes pose special and very important problems for global atmospheric models used for climate simulation and numerical weather prediction. At present, the observational database is inadequate to support research aimed at overcoming these problems. Three interdependent Arctic field programs now being planned will help to remedy this situation: SHEBA, which will operate an ice camp in the Arctic for a year; ARM, which will supply instruments for use at the SHEBA ice camp and which will also conduct longer-term measurements near Barrow, Alaska; and FIRE, which will conduct one or more aircraft campaigns, in conjunction with remote-sensing investigations focused on the SHEBA ice camp. This paper provides an introductory overview of the physics of the Arctic from the perspective of large-scale modelers, outlines some of the modeling problems that arise in attempting to simulate these processes, and explains how the data to be provided by the three field programs can be used to test and improve large-scale models.
AGUFM, Dec 1, 2010
Several Level 2 (L2) SST products have been operationally produced from AVHRR clear-sky radiances... more Several Level 2 (L2) SST products have been operationally produced from AVHRR clear-sky radiances since the late 1970s, initially at NOAA/NESDIS, and later at NAVO and Meteo France. Reprocessing of AVHRR data back to 1981 is done under the Pathfinder SST Program. By virtue of their long time series, consistent global coverage, accuracy and spatial resolution, AVHRR L2 SST products
AGU Fall Meeting Abstracts, Dec 1, 2018
AGUFM, 2006
The NCEP climate forecast system (CFS) reanalysis (CFSR) was recently completed using the NCEP co... more The NCEP climate forecast system (CFS) reanalysis (CFSR) was recently completed using the NCEP coupled atmosphere-ocean-land surface-sea ice system. This paper describes the sea ice concentration data used and how sea ice concentration is assimilated in the CFSR. The near record minimum of Arctic sea ice is clearly shown in the CFSR output. Because of the realistic sea ice distribution, there have been many improvements in the CFSR compared to the previous NCEP/NCAR Reanalysis-1 and NCEP-DOE Reanalysis-2. For instance, the surface air temperature improved in the fall over the Arctic Ocean.
Deep-sea Research Part Ii-topical Studies in Oceanography, Nov 1, 2012
Many sea surface temperature (SST) gap-free gridded analysis (Level 4, or L4) fields are produced... more Many sea surface temperature (SST) gap-free gridded analysis (Level 4, or L4) fields are produced by various groups in different countries. The Group for High Resolution SST (GHRSST) is an international collaboration body which has formed the inter-comparison technical advisory group (IC-TAG), to advise SST producers and users on the relative performance of these SST fields. This two-part paper describes two of the three major systems developed under GHRSST coordination towards this goal. Part one (this paper) describes the GHRSST Multi-Product Ensemble (GMPE) system, which runs on a daily basis at the UK Met Office, taking various L4 analyses as inputs, transferring them onto a common grid, and producing an ensemble median and standard deviation. The various analysis systems contributing to the GHRSST inter-comparisons are discussed, highlighting areas of commonality between the systems as well as those parts of the systems where there is less agreement on the appropriate algorithmic or parametric choices. The characteristics of the contributing L4 analyses are demonstrated by comparing them to near-surface Argo profile temperature data, which provide an independent measurement of SST and have been shown to provide a good estimate of foundation SST (the SST free of diurnal warming). The feature resolution characteristics of the L4 analyses are demonstrated by calculating horizontal gradients of the SST fields (on their original grid). The accuracy and resolution of the GMPE median are compared with those of the input analyses using the same metrics, showing that the GMPE median is more accurate than any of the contributing analyses with a standard deviation error of 0.40 K globally with respect to near-surface Argo data. For use in climate applications such as trend analysis or assimilation into climate models, it is important to have a good measure of uncertainty, so the suitability of the GMPE standard deviation as a measure of uncertainty is explored. This assessment shows that, over large spatial and temporal scales, the spread in the ensemble does have a strong relationship with the error in the median, although it underestimates the error by about one third.
AGU Fall Meeting Abstracts, Dec 1, 2020
Atmosphere, Mar 28, 2021
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
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Papers by Robert Grumbine