Mark A. Merrifield

Tide gauge observations of the Indian Ocean tsunami, December 26, 2004

The magnitude 9.0 earthquake centered off the west coast of northern Sumatra (3.307°N, 95.947°E) on December 26, 2004 at 00:59 UTC (United States Geological Survey (USGS) (2005), USGS Earthquake Hazards Program-Latest Earthquakes, Earthquake Hazards Program, http://earthquake.usgs.gov/eqinthenews/2004/usslav/, 2005) generated a series of tsunami waves that devastated coastal areas throughout the Indian Ocean. Tide gauges operated on behalf of national and international organizations recorded the wave form at a number of island and continental locations. This report summarizes the tide gauge observations of the tsunami in the Indian Ocean (available as of January 2005) and provides a recommendation for the use of the basin-wide tide gauge network for future warnings.

Interference Pattern and Propagation of the M2 Internal Tide South of the Hawaiian Ridge

Abstract Most of the M2 internal tide energy generated at the Hawaiian Ridge radiates away in modes 1 and 2, but direct observation of these propagating waves is complicated by the complexity of the bathymetry at the generation region and by the presence of interference patterns. Observations from satellite altimetry, a tomographic array, and the R/P FLIP taken during the Farfield Program of the Hawaiian Ocean Mixing Experiment (HOME) are found to be in good agreement with the output of a high-resolution primitive equation model, simulating the generation and propagation of internal tides. The model shows that different modes are generated with different amplitudes along complex topography. Multiple sources produce internal tides that sum constructively and destructively as they propagate. The major generation sites can be identified using a simplified 2D idealized knife-edge ridge model. Four line sources located on the Hawaiian Ridge reproduce the interference pattern of sea surface height and energy fl...

Sea-Level Rise by 2100

In his News and Analysis piece reporting on the newly released fifth assessment report (AR5) by Working Group I (WGI) of the Intergovernmental Panel on Climate Change (IPCC) (“A Stronger IPCC Report,” 4 October, p. [23][1]), R. A. Kerr highlights three fundamental conclusions about climate change that were assessed with equal or greater confidence than in previous IPCC reports. He also points to three “contentious points” on which he states that the AR5 “took a moderate line.” Kerr includes sea-level projections among these points, and reports “a rise of 40 to 60 centimeters by late in the century and a worst case of 1 meter by 2100, [which is] higher than in 2007 but far below the meter or two of sea-level rise that some expect.” As the authors of the IPCC WGI AR5 chapter on “Sea-Level Change,” we wish to clarify that for the highest emission scenario considered (RCP8.5), the AR5 reported a “likely” range of 0.45 to 0.82 m for sea-level projections for the late 21st century (average over 2081 to 2100) and of 0.52 to 0.98 m by 2100. The difference in sea level between these two periods is large because in 2081 to 2100, the “likely” rate of rise is 8 to 16 mm per year, which is up to about 10 times the average rate of rise during the 20th century. In the calibrated uncertainty language of the IPCC, this assessed likelihood means that there is roughly a one-third probability that sea-level rise by 2100 may lie outside the “likely” range. That is, the AR5 did not exclude the possibility of higher sea levels. However, we concluded that sea levels substantially higher than the “likely” range would only occur in the 21st century if the sections of the Antarctic ice sheet that have bases below sea level were to collapse. We determined with medium confidence that “this additional contribution would not exceed several 10ths of a meter of sea-level rise during the 21st century.” We could not define this possible contribution more precisely because “there is currently insufficient evidence to evaluate the probability of specific levels above the assessed ‘likely’ range.” The upper boundary of the AR5 “likely” range should not be misconstrued as a worst-case upper limit, as was done in Kerrs story as well as elsewhere in the media and blogosphere. For policy and planning purposes, it may be necessary to adopt particular numbers as an upper limit, but according to our assessment, the current state of scientific knowledge cannot give a precise guide. ![Figure][2] CREDIT: ANDREW MANDEMAKER/WIKIMEDIA COMMONS [1]: /lookup/doi/10.1126/science.342.6154.23-b [2]: pending:yes

Measuring progress of the global sea level observing system

Sea level is such a fundamental parameter in the sciences of oceanography geophysics, and climate change, that in the mid-1980s, the Intergovernmental Oceanographic Commission (IOC) established the Global Sea Level Observing System (GLOSS). GLOSS was to improve the quantity and quality of data provided to the Permanent Service for Mean Sea Level (PSMSL), and thereby, data for input to studies of long-term sea level change by the Intergovernmental Panel on Climate Change (IPCC). It would also provide the key data needed for international programs, such as the World Ocean Circulation Experiment (WOCE) and later, the Climate Variability and Predictability Programme (CLIVAR). GLOSS is now one of the main observation components of the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) of IOC and the World Meteorological Organization (WMO). Progress and deficiencies in GLOSS were presented in July to the 22nd IOC Assembly at UNESCO in Paris and are contained in the GLOSS Assessment Report (GAR) [IOC, 2003a].

An ongoing shift in Pacific Ocean sea level

Based on the satellite altimeter data, sea level off the west coast of the United States has increased over the past 5 years, while sea level in the western tropical Pacific has declined. Understanding whether this is a short-term shift or the beginning of a longer-term change in sea level has important implications for coastal planning efforts in the coming decades. Here, we identify and quantify the recent shift in Pacific Ocean sea level, and also seek to describe the variability in a manner consistent with recent descriptions of El Nino-Southern Oscillation (ENSO) and particularly the Pacific Decadal Oscillation (PDO). More specifically, we extract two dominant modes of sea level variability, one related to the biennial oscillation associated with ENSO and the other representative of lower-frequency variability with a strong signal in the northern Pacific. We rely on cyclostationary empirical orthogonal function (CSEOF) analysis along with sea level reconstructions to describe these modes and provide historical context for the recent sea level changes observed in the Pacific. As a result, we find that a shift in sea level has occurred in the Pacific Ocean over the past few years that will likely persist in the coming years, leading to substantially higher sea level off the west coast of the United States and lower sea level in the western tropical Pacific.

Forcing of recent decadal variability in the Equatorial and North Indian Ocean

Recent decadal sea surface height (SSH) variability across the Equatorial and North Indian Ocean (ENIO, north of 5°S) is spatially coherent and related to a reversal in basin-scale, upper-ocean-temperature trends. Analysis of ocean and forcing fields from a data-assimilating ocean synthesis (ECCOv4) suggests that two equally-important mechanisms of wind-driven heat redistribution within the Indian Ocean account for a majority of the decadal variability. The first is the Cross-Equatorial Cell (CEC) forced by zonal-wind-stress curl at the equator. The wind-stress curl variability relates to the strength and position of the Mascarene High, which is influenced by the phase of the Indian Ocean Subtropical Dipole. The second mechanism is deep (700 m) upwelling related to zonal wind stress at the equator that causes deep, cross-equatorial overturning due to the unique geometry of the basin. The CEC acts to cool the upper ocean throughout most of the first decade of satellite altimetry, while the deep upwelling delays and then amplifies the effect of the CEC on SSH. During the subsequent decade, reversals in the forcing anomalies drive warming of the upper ocean and increasing SSH, with the effect of the deep upwelling leading the CEC. This article is protected by copyright. All rights reserved.

Temporal variability of marine debris deposition at Tern Island in the Northwestern Hawaiian Islands.

A twenty-two year record of marine debris collected on Tern Island is used to characterize the temporal variability of debris deposition at a coral atoll in the Northwestern Hawaiian Islands. Debris deposition tends to be episodic, without a significant relationship to local forcing processes associated with winds, sea level, waves, and proximity to the Subtropical Convergence Zone. The General NOAA Operational Modeling Environment is used to estimate likely debris pathways for Tern Island. The majority of modeled arrivals come from the northeast following prevailing trade winds and surface currents, with trajectories indicating the importance of the convergence zone, or garbage patch, in the North Pacific High region. Although debris deposition does not generally exhibit a significant seasonal cycle, some debris types contain considerable 3 cycle/yr variability that is coherent with wind and surface pressure over a broad region north of Tern.