Diagnostic Studies with GLA Fields

Assessments of the NASA Goddard Earth Observing System-1 Data Assimilation System(GEOS-1 DAS), regarding heating rates, energetics, and angular momentum quantities were made. These diagnostics can be viewed as measures of climate variability. Comparisons with the NOAA/NCEP reanalysis system of momentum and energetics diagnostics are included. Water vapor and angular momentum are diagnosed in many models, including those of NASA, as part of the Atmospheric Model Intercomparison Project. 'Me GEOS-I and NOAA/NCEP global atmospheric angular momentum values are coherent on time scales down to about three days. Furthermore, they agree with the series of Earth angular momentum, as measured by tiny fluctuations in the rotation rate of the Earth, as variations in the length of day. The torques that effect such changes in atmospheric and Earth momentum are dominated by the influence of particular mountain systems, including the Rockies, Himalayas, and Andes, upon mountain torques on time scales shorter than about two weeks. Other project areas included collaboration with Goddard Space Flight Center to examine the impact of mountainous areas and the treatments of parameterizations on diagnoses of the atmosphere. Relevant preprints are included herein

Diagnostic Studies With GLA Fields

Assessments of the NASA Goddard Earth Observing System-1 Data Assimilation System (GEOS-1 DAS) regarding heating rates, energetics and angular momentum quantities were made. These diagnostics can be viewed as measures of climate variability. Comparisons with the NOAA/NCEP reanalysis system of momentum and energetics diagnostics are included. Water vapor and angular momentum are diagnosed in many models, including those of NASA, as part of the Atmospheric Model Intercomparison Project. Relevant preprints are included herein

Use of operational analyses to study the dynamics of troposphere-stratosphere interactions in polar regions

Operational analyses produced by large weather centers have been used in the past to monitor various aspects of the general circulation as well as address dynamical questions. For a number years researchers have been monitoring National Meteorological Center (NMC) analyses at 100 millibars because it is the level from which stratospheric analyses are built. In particular, they closely examined the pressure-work term at that level which is an important parameter related to the forcing of the stratosphere by the troposphere. Rapid fluctuations typically seen in this quanity during the months of July-November, and similarly noted by Randel et al., (1987) may raise some concern about the quality of the analyses. Researchers investigated the behavior of the term mainly responsible for these variations, namely the eddy flux of heat, and furthermore have corroborated the presence of these variations in contemporaneous analyses produced by the European Centre for Medium Range Forecasts (ECMWF). Researchers demonstrated that fluctuations in standing eddy heat fluxes, related to the forcing of the stratosphere by the troposphere, agree in two largely independent meteorological analyses. Researchers believe, that these fluctuations are mostly real

Composition, Chemistry, and Climate of the Atmosphere. 2: Mean properties of the atmosphere

The atmosphere can be defined as the relatively thin gaseous envelope surrounding the entire planet Earth. It possesses a number of properties related to its physical state and chemical composition, and it undergoes a variety of internal processes and external interactions that can either maintain or alter these properties. Whereas descriptions of the atmosphere's chemical properties form much of the remaining chapters of this book, the present chapter will highlight the atmosphere's gases, and these define its temperature structure. In contrast, the larger-scale motions comprise the winds, the global organization of which is often referred to as the general circulation. The framework of the dynamical and thermodynamical laws, including the three principles of conversation of mass, momentum, and energy, are fundamental in describing both the internal processes of the atmosphere and its external interactions. The atmosphere is not a closed system, because it exchanges all three of these internally conservative quantities across the atmosphere's boundary below and receives input from regions outside it. Thus surface fluxes of moisture, momentum, and heat occur to and from the underlying ocean and land. The atmosphere exchanges very little mass and momentum with space, though it absorbs directly a portion of the solar radiational energy received from above

Meteorological Data for Geodynamics Use: IERS Special Bureau for the Atmosphere

During the life of this contract, the PI set up and operated a data center known as the "Special Bureau for the Atmosphere" of the International Earth Rotation Service (IERS) at Atmospheric and Environmental Research, Inc., and in conjunction with the U.S. National Oceanic and Atmospheric Administration. The role of the center is to calculate, archive, analyze, and distribute atmospheric data related to Earth rotation, polar motion and other motions of the Earth. We have produced data from 4 different operational meteorological centers. We have also produced data from atmospheric reanalyzes, spanning back about a half a century. The center is one of several centers under the Global Geophysical Fluids Center (GGFC) of the IERS; the GGFC is centered at NASA's Goddard Space Flight Center. Our data center has made data available to a large variety of scientists worldwide

Regional Multi-Fluid-Based Geophysical Excitation of Polar Motion

By analyzing geophysical fluids geographic distribution, we can isolate the regional provenance for some of the important signals in polar motion. An understanding of such will enable us to determine whether certain climate signals can have an impact on polar motion. Here we have compared regional patterns of three surficial fluids: the atmosphere, ocean and land-based hydrosphere. The oceanic excitation function of polar motion was estimated with the ECCO/JPL data - assimilating model, and the atmospheric excitation function was determined from NCEP/NCAR reanalyses. The excitation function due to land hydrology was estimated from the Gravity Recovery and Climate Experiment (GRACE) data by an indirect approach that determines water thickness. Our attention focuses on the regional distribution of atmospheric and oceanic excitation of the annual and Chandler wobbles during 1993-2010, and on hydrologic excitation of these wobbles during 2002.9-2011.5. It is found that the regions of maximum fractional covariance (those exceeding a value of 3 .10 -3) for the annual band are over south Asia, southeast Asia and south central Indian ocean, for hydrology, atmosphere and ocean respectively; and for the Chandler period, areas over North America, Asia, and South America; and scattered across the southern oceans for the atmosphere and oceans respectivel

Modeling ocean-induced rapid Earth rotation variations: an update

We revisit the problem of modeling the ocean’s contribution to rapid, non-tidal Earth rotation variations at periods of 2–120 days. Estimates of oceanic angular momentum (OAM, 2007–2011) are drawn from a suite of established circulation models and new numerical simulations, whose finest configuration is on a 1⁄ 6◦ grid. We show that the OAM product by the Earth System Modeling Group at GeoForschungsZentrum Potsdam has spurious short period variance in its equatorial motion terms, rendering the series a poor choice for describing oceanic signals in polar motion on time scales of less than ∼2 weeks. Accounting for OAM in rotation budgets from other models typically reduces the variance of atmosphere-corrected geodetic excitation by ∼54% for deconvolved polar motion and by ∼60% for length-of-day. Use of OAM from the 1⁄ 6◦ model does provide for an additional reduction in residual variance such that the combined oceanic–atmospheric effect explains as much as 84% of the polar motion excitation at periods < 120 days. Employing statistical analysis and bottom pressure changes from daily Gravity Recovery and Climate Experiment solutions, we highlight the tendency of ocean models run at a 1◦ grid spacing to misrepresent topographically constrained dynamics in some deep basins of the Southern Ocean, which has adverse effects on OAM estimates taken along the 90◦ meridian. Higher model resolution thus emerges as a sensible target for improving the oceanic component in broader efforts of Earth system modeling for geodetic purposes.Austrian Science Fund http://dx.doi.org/10.13039/501100002428National Aeronautics and Space Administration http://dx.doi.org/10.13039/100000104https://isdc.gfz-potsdam.de/ggfc-oceans/https://doi.org/10.5281/zenodo.4707150http://rz-vm115.gfz-potsdam.de:8080/repository/https://ifg.tugraz.at/ITSG-Grace2018ftp://isdcftp.gfz-potsdam.de/grace/Level-1B/GFZ/AOD/RL06/https://ecco-group.org/products-ECCO-V4r4.ht

Convergence of Daily GRACE Solutions and Models of Submonthly Ocean Bottom Pressure Variability

Knowledge of submonthly variability in ocean bottom pressure (pb) is an essential element in space‐geodetic analyses and global gravity field research. Estimates of these mass changes are typically drawn from numerical ocean models and, more recently, GRACE (Gravity Recovery and Climate Experiment) series at daily sampling. However, the quality of pb fields from either source has been difficult to assess and reservations persist as to the dependence of regularized GRACE solutions on their oceanographic priors. Here, we make headway on the subject by comparing two daily satellite gravimetry products (years 2007–2009) both with each other and with pb output from a diverse mix of ocean models, complemented by insights from bottom pressure gauges. Emphasis is given to large spatial scales and periods <60 days. Satellite‐based mass changes are in good agreement over basin interiors and point to excess pb signals (∼2 cm root‐mean‐square error) over Southern Ocean abyssal plains in the present GRACE de‐aliasing model. These and other imperfections in baroclinic models are especially apparent at periods <10 days, although none of the GRACE series presents a realistic ground truth on time scales of a few days. A barotropic model simulation with parameterized topographic wave drag is most commensurate with the GRACE fields over the entire submonthly band, allowing for first‐order inferences about error and noise in the gravimetric mass changes. Estimated pb errors vary with signal magnitude and location but are generally low enough (0.5–1.5 cm) to judge model skill in dynamically active regions.Plain Language Summary: Changes in the pressure at the seafloor tell us how ocean masses move in time and space. These environmental signals are important for understanding variations in Earth's shape, rotation, and gravity field. We assess how well we know the rapid, submonthly portion of bottom pressure changes by analyzing output from oceanographic models and observations from the Gravity Recovery and Climate Experiment (GRACE) dual satellite mission. We show that two different GRACE solutions, sampled daily, are in good agreement with each other over the deep interior of the ocean basins. Moreover, bottom pressure changes simulated with a simple single‐layer model are remarkably consistent with GRACE, providing an independent measure of the quality of both products. Based on these grounds, and by aid of an approximate error assessment, we suggest that nonstandard daily GRACE fields are realistic enough to help identifying deficiencies in oceanographic models and guide solutions to these issues. We particularly highlight an overestimation of Southern Ocean bottom pressure variability in two widely used general circulation simulations and speculate on ways how to improve the underlying models.Key Points: We rigorously compare daily Gravity Recovery and Climate Experiment (GRACE) gravity solutions with bottom pressure output from five ocean models at periods <60 days Southern Ocean mass‐field variability in current de‐aliasing model is too energetic; dedicated barotropic simulations better match GRACE Daily gravity fields have errors of 0.5–1.5 cm (water height) over basin interiors and may guide improvements to existing ocean modelsAustrian Science Fund (FWF) http://dx.doi.org/10.13039/501100002428National Aeronautics and Space Administration (NASA) http://dx.doi.org/10.13039/100000104Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/50110000165

Impact of Climatic Variability on Atmospheric Mass Distribution and GRACE-Derived Gravity Fields

During the period we calculated the atmospheric data sets related to its mass and angular momentum distribution. For mass, we determined the various harmonics from the NCEP-NCAR reanalysis, especially the low-order harmonics that are useful in studying the gravitation distribution as will be determined from the GRACE mission. Atmospheric mass is also related to the atmospheric loading on the solid Earth; we cooperated with scientists who needed the atmospheric mass information for understanding its contributions to the overall loading, necessary for vertical and horizontal coordinate estimation. We calculated atmospheric angular momentum from the NCEP-NCAR reanalyses and 4 operational meteorological centers, based on the motion (wind) terms and the mass (surface pressure) terms. These are associated with motions of the planet, including its axial component causing changes in the length of day, more related to the winds, and the equatorial component related to motions of the pole, more related to the mass. Tasks related to the ocean mass and angular momentum were added to the project as well. For these we have noted the ocean impact on motions of the pole as well as the torque mechanisms that relate the transfer of angular momentum between oceans and solid earth. The activities of the project may be summarized in the following first manuscript written in December 2002, for a symposium that Dr. Salstein attended on Geodynamics. We have continued to assess ocean angular momentum (OAM) quantities derived from bottom pressure and velocity fields estimated with our finite-difference barotropic (single layer) model. Three years of output (1993-95) from a run without any data constraints was compared to output from a corresponding run that was constrained by altimeter data using a Kalman filter and smoother scheme. Respective OAM time series were combined with corresponding atmospheric series and compared to observed polar motion. The constrained OAM series provided slightly better variance reduction than the unconstrained series. Analysis provided a check on the estimation scheme and pointed to further work to improve the determination of OAM using this method. A significant effort was also devoted to quantifying effects of uncertainties in high frequency winds on the mean and seasonal momentum exchange between atmosphere and oceans