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K. McGuffie and D. A. Robinson

Abstract

Cloud retrieval from satellite data in the regions of snow and ice cover is generally acknowledged to be difficult with the present generation of meteorological satellites. Despite potential advances to be made in this field (e.g., 1.6 μm sensor to be operated on NOAA satellites) large-scale cloud analysis techniques are likely to require information on the location of the margin of seasonal snow cover. In this paper we investigate the accuracy of one snow-cover dataset currently utilized by a global nephanalysis model, the United States Air Force (USAF) RT Nephanalysis, and investigate the effect of inaccurates in the snow cover information on the derived cloud field. There are found to be situations where the snow model is inaccurate because of the advanced gate of the spring melt with respect to climatology which causes errors in the derived cloud amount. The USAF policy of including surface cloud observations in the RT Nephanalysis leads to correction of the erroneous cloud amount in regions where surface observations are available.

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A. R. Robinson and D. B. Haidvogel

Abstract

The initial/boundary value problem for the barotropic version of a quasi-geostrophic open ocean model which requires normal flow everywhere on the boundary and vorticity on the inflow is studied. Parameter dependencies and sensitivities are determined for dynamical forecast experiments carried out over a 500 square kilometer domain with data simulated to represent the mid-ocean eddy field at 1500 m. The computational rms forecast error due to open boundary conditions is kept to 5% after one year of integration. Errors, gaps and noise are then introduced into the boundary and initial condition data. Objective analysis is introduced for mapping coarsely-distributed data onto the computational grid, and vorticity is derived from the streamfunction by several methods. Forecast error is sensitive to the frequency of updating of boundary data, but generally insensitive to vorticity errors. A simulated forecast experiment with composite error sources representative of feasible oceanic conditions is carried out for four months duration with rms error maintained to about 10%.

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D. E. Harrison and A. R. Robinson

Abstract

A simple linear model of the barotropic basin response to forcing imposed along the northern boundary is described. The dependence on latitude of the response may include oscillatory behavior or not, depending on whether the forcing frequency is smaller or greater than the fundamental free basin mode frequency. When oscillatory behavior is found, the forced solution may resemble oceanic mesoscale eddies. The relevance of this simple model to a description of the eddy fields of several mesoscale resolution general ocean circulation numerical experiments is examined. It is found that a single term of the analytical solution can very well describe the numerically produced eddy fields, away from the regions of strong currents. The possibility that this general mechanism might account for the existence of mesoscale eddies in the ocean is briefly discussed.

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A. R. Robinson, D. E. Harrison, Y. Mintz, and A. J. Semtner

Abstract

We present the results of a multi-level, constant depth, primitive equation general ocean numerical circulation simulation with mesoscale resolution. A single mid-latitude model gyre is driven by wind and heating. After 30 years of spin-up with a relatively coarse grid and large diffusion coefficients, the grid size and diffusion coefficients are reduced. The circulation then adjusts into a nonlinear and time-dependent flow with periods of tens of days and space scales of hundreds of kilometers. After a quasi-equilibrium state is achieved, two years of data are obtained which are separated into time-mean and time-dependent fluctuations, and analyzed. Dynamically distinct regions are intensified, momentum, heat and vorticity balances examined, and energy integrals calculated. Statistical measures of significance and of uncertainty are computed where possible. Eddy energy is produced primarily by Reynolds stress work (barotropic instability) on the mean circulation shear in the recirculation and near-field region of the northern current system. Mean fluctuation correlation terms are presented in some regions at order 1 in the mean heat and vorticity balance and can be the leading ageostrophic effect in the mean momentum balance. The flow is non-quasigeostrophic in some parts of the intense boundary currents.

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J. R. Mioduszewski, A. K. Rennermalm, D. A. Robinson, and L. Wang

Abstract

Spring snowmelt onset has occurred earlier across much of the Northern Hemisphere land area in the last four decades. Understanding the mechanisms driving spring melt has remained a challenge, particularly in its spatial and temporal variability. Here, melt onset dates (MOD) obtained from passive microwave satellite data are used, as well as energy balance and meteorological fields from NASA’s Modern-Era Retrospective Analysis for Research and Applications, to assess trends in the MOD and attribute melt onset across much of Arctic and sub-Arctic Eurasia and North America during the spring snowmelt season from 1979 to 2012. Across much of the Northern Hemisphere MOD has occurred 1–2 weeks earlier over this period, with the strongest trends in western and central Russia and insignificant trends across most of North America. Trends in MOD are reflected by those in energy balance terms, with energy advection providing an increasing proportion of melt energy in regions with the strongest MOD trends. Energy advection plays a larger role in melt onset in regions where snow begins melting in March and April, while insolation and longwave radiation drives melt where the MOD occurs in May and June. This implies that there is a potential shift in snowmelt drivers toward those involved in advective processes rather than radiative processes with an earlier MOD. As the high latitudes warm and terrestrial snow cover continues to melt and disappear earlier in the spring, it is valuable to elucidate regional snowmelt sensitivities to better understand regional responses to changing climatological processes.

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A. R. Robinson, N. E. Huang, C. D. Leitao, and C. G. Parra

Abstract

Altimeter data obtained from GEOS-3 during the three year period 1975–78 for a region of the western North Atlantic which includes a portion of the Gulf Stream system and part of the open ocean area of the subtropical gyre are analyzed by a new technique which utilizes all the points along the satellite tracks. The physical phenomenon studied are the time-variable but almost geostrophic currents, or mesoscale eddies, so that geoid errors contaminate the scientific signal minimally and the dynamical interpretation is direct. Results presented include the spatial distribution of geostrophic eddy kinetic energy and examples of a synoptic map of the eddy field (April 1977) and of a time series at a point. These results are compared to and synthesized with a diverse and selected set of existing measurements and observations obtained in situ by a variety of instrumental techniques. The agreement is generally good, and the altimeter data analyzed provides new information on features in the map of mean eddy kinetic energy. The implications are that satellite altimetry will serve as a powerful quantitative tool in eddy current research and that even presently archived data contains further useful scientific information.

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H. W. Loescher, J. M. Jacobs, O. Wendroth, D. A. Robinson, G. S. Poulos, K. McGuire, P. Reed, B. P. Mohanty, J. B. Shanley, and W. Krajewski

The Consortium of Universities for the Advancement of Hydrologic Sciences, Inc., established the Hydrologic Measurement Facility to transform watershed-scale hydrologic research by facilitating access to advanced instrumentation and expertise that would not otherwise be available to individual investigators. We outline a committee-based process that determined which suites of instrumentation best fit the needs of the hydrological science community and a proposed mechanism for the governance and distribution of these sensors. Here, we also focus on how these proposed suites of instrumentation can be used to address key scientific challenges, including scaling water cycle science in time and space, broadening the scope of individual subdisciplines of water cycle science, and developing mechanistic linkages among these subdisciplines and spatiotemporal scales.

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C. Donlon, I. Robinson, K. S. Casey, J. Vazquez-Cuervo, E. Armstrong, O. Arino, C. Gentemann, D. May, P. LeBorgne, J. Piollé, I. Barton, H. Beggs, D. J. S. Poulter, C. J. Merchant, A. Bingham, S. Heinz, A. Harris, G. Wick, B. Emery, P. Minnett, R. Evans, D. Llewellyn-Jones, C. Mutlow, R. W. Reynolds, H. Kawamura, and N. Rayner

A new generation of integrated sea surface temperature (SST) data products are being provided by the Global Ocean Data Assimilation Experiment (GODAE) High-Resolution SST Pilot Project (GHRSST-PP). These combine in near-real time various SST data products from several different satellite sensors and in situ observations and maintain the fine spatial and temporal resolution needed by SST inputs to operational models. The practical realization of such an approach is complicated by the characteristic differences that exist between measurements of SST obtained from subsurface in-water sensors, and satellite microwave and satellite infrared radiometer systems. Furthermore, diurnal variability of SST within a 24-h period, manifested as both warm-layer and cool-skin deviations, introduces additional uncertainty for direct intercomparison between data sources and the implementation of data-merging strategies. The GHRSST-PP has developed and now operates an internationally distributed system that provides operational feeds of regional and global coverage high-resolution SST data products (better than 10 km and ~6 h). A suite of online satellite SST diagnostic systems are also available within the project. All GHRSST-PP products have a standard format, include uncertainty estimates for each measurement, and are served to the international user community free of charge through a variety of data transport mechanisms and access points. They are being used for a number of operational applications. The approach will also be extended back to 1981 by a dedicated reanalysis project. This paper provides a summary overview of the GHRSST-PP structure, activities, and data products. For a complete discussion, and access to data products and services see the information online at www.ghrsst-pp.org.

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Jay H. Lawrimore, Michael S. Halpert, Gerald D. Bell, Matthew J. Menne, Bradfield Lyon, Russell C. Schnell, Karin L. Gleason, David R. Easterling, Wasila Thiaw, William J. Wrightand, Richard R. Heim Jr., David A. Robinson, and Lisa Alexander

The global climate in 2000 was again influenced by the long-running Pacific cold episode (La Niña) that began in mid-1998. Consistent with past cold episodes, enhanced convection occurred across the climatologically convective regions of Indonesia and the western equatorial Pacific, while convection was suppressed in the central Pacific. The La Niña was also associated with a well-defined African easterly jet located north of its climatological mean position and low vertical wind shear in the tropical Atlantic and Caribbean, both of which contributed to an active North Atlantic hurricane season. Precipitation patterns influenced by typical La Niña conditions included 1) above-average rainfall in southeastern Africa, 2) unusually heavy rainfall in northern and central regions of Australia, 3) enhanced precipitation in the tropical Indian Ocean and western tropical Pacific, 4) little rainfall in the central tropical Pacific, 5) below-normal precipitation over equatorial east Africa, and 6) drier-than-normal conditions along the Gulf coast of the United States.

Although no hurricanes made landfall in the United States in 2000, another active North Atlantic hurricane season featured 14 named storms, 8 of which became hurricanes, with 3 growing to major hurricane strength. All of the named storms over the North Atlantic formed during the August–October period with the first hurricane of the season, Hurricane Alberto, notable as the third-longest-lived tropical system since reliable records began in 1945. The primary human loss during the 2000 season occurred in Central America, where Hurricane Gordon killed 19 in Guatemala, and Hurricane Keith killed 19 in Belize and caused $200 million dollars of damage.

Other regional events included 1) record warm January–October temperatures followed by record cold November–December temperatures in the United States, 2) extreme drought and widespread wildfires in the southern and western Unites States, 3) continued long-term drought in the Hawaiian Islands throughout the year with record 24-h rainfall totals in November, 4) deadly storms and flooding in western Europe in October, 5) a summer heat wave and drought in southern Europe, 6) monsoon flooding in parts of Southeast Asia and India, 7) extreme winter conditions in Mongolia, 8) extreme long-term drought in the Middle East and Southwest Asia, and 9) severe flooding in southern Africa.

Global mean temperatures remained much above average in 2000. The average land and ocean temperature was 0.39°C above the 1880–1999 long-term mean, continuing a trend to warmer-than-average temperatures that made the 1990s the warmest decade on record. While the persistence of La Niña conditions in 2000 was associated with somewhat cooler temperatures in the Tropics, temperatures in the extratropics remained near record levels. Land surface temperatures in the high latitudes of the Northern Hemisphere were notably warmer than normal, with annually averaged anomalies greater than 2°C in parts of Alaska, Canada, Asia, and northern Europe.

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R. S. Lieberman, W. A. Robinson, S. J. Franke, R. A. Vincent, J. R. Isler, D. C. Fritts, A. H. Manson, C. E. Meek, G. J. Fraser, A. Fahrutdinova, W. Hocking, T. Thayaparan, J. MacDougall, K. Igarashi, T. Nakamura, and T. Tsuda

Abstract

High Resolution Doppler Imager (HRDI) measurements of daytime and nighttime winds at 95 km are used to deduce seasonally averaged Eulerian mean meridional winds during six solstice periods. These estimates are compared with seasonally averaged radar meridional winds and with results from dynamical and empirical wind models. HRDI mean meridional winds are directed from the summer pole toward the winter pole over much of the globe. Peak equatorward winds of about 15 m s−1 are usually observed in the summer hemisphere near 30°. A local minimum in the equatorward winds is often observed poleward of this latitude, with winds approaching zero or reversing direction. A similar structure is seen in contemporaneous radar winds. This behavior differs from residual meridional wind patterns predicted by models. The discrepancies may be related to gravity wave paramaterizations or a consequence of planetary wave influences.

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