Intercomparison of two-dimensional wave spectra obtained from microwave instruments, buoys and WAModel simulations during the surface wave dynamics experiment

An intercomparison is made of two dimensional wave spectra obtained from buoys and various remote sensing microwave systems and predicted by the WAModel dur- ing the Surface Wave Dynamics Experiment (SWADE). The overall agreement be- tween the measurements and the model is satifactory, but some differences in detail require further investigation. The buoy data yield reliable mean spectral parame- ters, but the maximum likelihood retrieval algorithm tends to produce directional distributions that are broader than those of other instruments. Various microwave instruments (ROWS, RESSAC, SRA) show good promise for the determination of 2d-wave spectra, but exhibit individual shortcomings (calibration uncertainties, di- rectional ambiguity, impact of aircraft motion) that need to be further studied. The SAR system yields reliable retrievals with respect to the general spectral dis- tribution, but suffers in this experiment from an undetermined calibration factor. Deviations between the WAModel and instrumental data could be largely attributed to wind field errors, but the model also exhibits deficiencies in the development of short-fetch wave systems and in the wave spectral response to rapidly turning wind fields

Measurements of wind-wave growth and swell decay during the joint North Sea wave project (JONSWAP).

Wavo spectra were measured along a profile extending 160 km into the North Sea westward from Sylt for a period of ten weeks in 1969. Currents, tides, air-sea temperature differences and turbulence in the atmospheric boundary layer were also measured. the goal of the experiment (described in Part 1) was to determine the structure of the source function governing the energy balance of the wave spectrum, with particular emphasis on wave growth under stationary offshore wind conditions (Part 2) and the attention of swell in water of finito depth (Part 3). The source functions of wave spectra generated by offshore winds exhibit a characteristic plus-minus signature associated with the shift of the sharp spectral peak towards lower frequencies. The two-lobed distribution of the source function can be explained quantitively by the nonlinear transfer due to resonant wave-wave interactions (second order Bragg scattering). The evolution of a pronounced peak and its shift towards lower frequencies can also be understood as a self-stabilizing feature of this process. The decay rates determined for incoming swell varied considerably, but energy attenuation factors of two along the length of the profile were typical. This is in order of magnitude agreement with expected damping rates due to bottom friction. However, the strong tidal modulation predicted by theory for the case of a quadratic bottom friction law was not observed. Adverse winds did not affect the decay rate. Computations also rule out wave-wave interactions or dissipation due to turbulence outside the bottom boundary layer as effective mechanisms of swell attenuation. We conclude that either the generally accepted friction law needs to be significantly modified or that some other mechanism, such as scattering by bottom irregularities, is the cause of the attenuation. The dispersion characteristics of thw swells indicated rather nearby origins, for which the classical DELTA-event model was generally inapplicable. A strong Doppler modulation by tidal currents was also observed. (A

Dynamics of lattice pinned charge stripes

We study the transversal dynamics of a charged stripe (quantum string) and show that zero temperature quantum fluctuations are able to depin it from the lattice. If the hopping amplitude t is much smaller than the string tension J, the string is pinned by the underlying lattice. At t>>J, the string is depinned and allowed to move freely, if we neglect the effect of impurities. By mapping the system onto a 1D array of Josephson junctions, we show that the quantum depinning occurs at t/J = 2 / pi^2. Besides, we exploit the relation of the stripe Hamiltonian to the sine-Gordon theory and calculate the infrared excitation spectrum of the quantum string for arbitrary t/J values.Comment: 4 pages, 2 figure

Energy spectra of the ocean's internal wave field: theory and observations

The high-frequency limit of the Garrett and Munk spectrum of internal waves in the ocean and the observed deviations from it are shown to form a pattern consistent with the predictions of wave turbulence theory. In particular, the high frequency limit of the Garrett and Munk spectrum constitutes an {\it exact} steady state solution of the corresponding kinetic equation.Comment: 4 pages, one color figur

Global climate models violate scaling of the observed atmospheric variability

We test the scaling performance of seven leading global climate models by using detrended fluctuation analysis. We analyse temperature records of six representative sites around the globe simulated by the models, for two different scenarios: (i) with greenhouse gas forcing only and (ii) with greenhouse gas plus aerosol forcing. We find that the simulated records for both scenarios fail to reproduce the universal scaling behavior of the observed records, and display wide performance differences. The deviations from the scaling behavior are more pronounced in the first scenario, where also the trends are clearly overestimated.Comment: Accepted for publishing in Physical Review Letter

Temperature variability implies greater economic damages from climate change

A number of influential assessments of the economic cost of climate change rely on just a small number of coupled climate–economy models. A central feature of these assessments is their accounting of the economic cost of epistemic uncertainty—that part of our uncertainty stemming from our inability to precisely estimate key model parameters, such as the Equilibrium Climate Sensitivity. However, these models fail to account for the cost of aleatory uncertainty—the irreducible uncertainty that remains even when the true parameter values are known. We show how to account for this second source of uncertainty in a physically well-founded and tractable way, and we demonstrate that even modest variability implies trillions of dollars of previously unaccounted for economic damages