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Lexington, MA, United States

Piecuch C.G.,Atmospheric and Environmental Research Inc.
Journal of Geophysical Research: Oceans | Year: 2013

Ocean bottom pressure variability, derived from Release-05 Gravity Recovery and Climate Experiment time-variable gravity coefficients over the ocean, is investigated along the tropical North Pacific for the case of long time scales (>1 yr) and large space scales (>750 km). To interpret the observations, a linear model of the bottom pressure response to interior wind stress curl is derived on the basis of normal vertical modes; the adjustment comprises contributions from barotropic Sverdrup dynamics as well as first baroclinic mode Rossby waves. Model solutions are evaluated numerically using time-mean ocean stratification from the Ocean Comprehensible Atlas and time-varying surface wind stress from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis. In the western tropical North Pacific, model and data compare favorably; simulated and observed time series are significantly correlated, and the model generally explains more than half of the data variance; the good correspondence between model and data speaks to the good quality of the satellite-derived fields. In the central and eastern tropical North Pacific, findings are more ambiguous; model and data time series are mostly not significantly correlated, and simulations generally explain less than half of the data variance; discrepancies between model and data could point to physics absent from the model, for example, signals generated at the eastern boundary. Results provide observational demonstration that baroclinic contributions to bottom pressure changes can be important at low latitudes and low frequencies; findings hint at a basin-scale influence of tropical climate modes on the ocean bottom pressure field. © 2013. American Geophysical Union. All Rights Reserved. Source

Hollweg J.V.,University of New Hampshire | Kaghashvili E.K.,Atmospheric and Environmental Research Inc.
Astrophysical Journal | Year: 2012

We revisit our earlier study of the evolution of an initial propagating Alfvén wave in a magnetic-field-aligned flow with a cross-field velocity shear. Our goal is to show how the Alfvén wave drives up plasma density fluctuations which might be observed and serve as a signature of the presence of Alfvén waves in regions such as the solar corona which are inaccessible to direct observations. Here, we introduce a new initial condition which takes into account the initial distortion of the streamlines by the Alfvén wave, and we present new analytical results for the driven waves. We find that the density fluctuations of a properly placed linearly polarized Alfvén wave in a shear flow are much smaller than we originally estimated. © 2012 The American Astronomical Society. All rights reserved. Source

Turner D.D.,University of Wisconsin - Madison | Mlawer E.J.,Atmospheric and Environmental Research Inc.
Bulletin of the American Meteorological Society | Year: 2010

A set of field experiments initiated by the Atmospheric Radiation Measurement (ARM) program, the Radiative Heating in Underexplored Bands Campaigns (RHUBC), are presented. These experiments were designed to improve an understanding of the dominant radiative processes in the middle troposphere, upper troposphere, and lower stratosphere. Data from the RHUBC campaigns are used in radiance closure exercises, wherein atmospheric state observations are used as input into state-of-the-art line-by-line radiative transfer models that are compared against collocated detailed spectral radiance observations. The RHUBC experiment provided opportunities to improve radiative transfer models in spectral regions that are important for remote sensing but are less important from a climate point of view. Source

Stammer D.,University of Hamburg | Cazenave A.,CNRS Geophysical Research and Oceanographic Laboratory | Ponte R.M.,Atmospheric and Environmental Research Inc. | Tamisiea M.E.,National Oceanographic Center
Annual Review of Marine Science | Year: 2013

Regional sea level changes can deviate substantially from those of the global mean, can vary on a broad range of timescales, and in some regions can even lead to a reversal of long-term global mean sea level trends. The underlying causes are associated with dynamic variations in the ocean circulation as part of climate modes of variability and with an isostatic adjustment of Earth's crust to past and ongoing changes in polar ice masses and continental water storage. Relative to the coastline, sea level is also affected by processes such as earthquakes and anthropogenically induced subsidence. Present-day regional sea level changes appear to be caused primarily by natural climate variability. However, the imprint of anthropogenic effects on regional sea level-whether due to changes in the atmospheric forcing or to mass variations in the system-will grow with time as climate change progresses, and toward the end of the twenty-first century, regional sea level patterns will be a superposition of climate variability modes and natural and anthropogenically induced static sea level patterns. Attribution and predictions of ongoing and future sea level changes require an expanded and sustained climate observing system. © 2013 by Annual Reviews. All rights reserved. Source

Ponte R.M.,Atmospheric and Environmental Research Inc.
Geophysical Research Letters | Year: 2012

An ocean state estimate constrained by most available data is explored to assess characteristics of variability in deep steric height-a mostly unobserved quantity, yet important for understanding the relation between sea level, heat content and other ocean climate parameters. Results are based on monthly-averaged steric height anomalies, vertically integrated over the "unobserved" deep ocean (below ∼1700 m). Excluding linear trends, variability in deep steric height is typically 10-20% of that in the upper ocean, with larger values seen in extensive regions. Enhanced deep variability, at monthly to interannual time scales, occurs in areas of strong eddy energy. Deep signals are mostly thermosteric in nature, with halosteric contributions tightly correlated and generally compensating in the Atlantic and Indian oceans and adding in the Pacific. Potential inference of deep signals from knowledge of the upper ocean is hampered by poor correlations, and regressions based on upper ocean steric height fail to represent the estimated deep variability. Monthly sampling at ∼2° scales would allow for best determination of deep variability and long term trends. Copyright 2012 by the American Geophysical Union. Source

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