Some statistical properties of surges

All surges observed at the Swedish Astrophysical Station in Anacapri from July 1, 1957 until December 31, 1967 have been studied statistically. In 1958 the Southern hemisphere was most active in producing surges, but thereafter the Northern hemisphere has dominated the activity with increasing rate. The average for the whole period shows that the Northern part of the sun has been twice as active as the Southern part. The latitude distribution for surges has varied with the solar cycle with a pattern similar to the butterfly diagram for sunspots. The polar surges were most frequent in the beginning of the new cycle. The importance distribution is also dependent of the solar cycle, as a higher percentage of surges of importance 1 are found during the solar minimum. Surges of higher importance tend to have longer durations, and they are more often associated with flares. The association rate between surges and radio emission is dependent on both the solar cycle and the importance of the surge. During years with high activity, more than 20% of all surges were followed within 5 min from their start by radio emission, compared to 4% during solar minimum. 17% of surges of importance 2 are closer related to radio emission, but only 10% of surges of importance 1. On the whole, 11% of the surges occurred almost simultaneously with radio bursts. Bursts in discrete frequencies were registered in connection with 8% of the surges, while 11% were followed within 5 min from their start by bursts in spectral observations. All these surges were isolated, i.e. no flares have been reported to occur during their lifetimes. This is also the case for the 18 surges covered by X-ray observations, three of which were closer related to X-ray bursts.     

Estimating Deep Seafloor Interface and Volume Roughness Parameters Using the Multibeam-Hydrosweep System

Utilizing a hull-mounted, multinarrow beam echosounder onboard RV Polarstern, we measured variation of acoustic backscatter with incidence angles at two different sites in the Southern Oceans (Agulhas Plateau and the Riiser Larsen Sea). We modeled the data, using a composite roughness model, including water-sediment interface roughness and sediment volume roughness parameters. The model effectively uses the near normal incidence angle backscatter to determine the seafloor interface roughness parameters employing Helmholtz-Kirchhoff theory. Beyond 20° incidence angles, an application of Rayleigh-Rice theory is made by using a necessary splicing technique (combining both of the theories at 20° incidence angle). The estimated interface and volume roughness parameters are found to be in accordance with the known area geology.     

Norwegian marine geodetic projects

The hitherto promising finds of oil and gas on the Norwegian continental shelf have increased the general activity in this area considerably. Consequently, the need for better charts and more precise navigational systems have become more pertinent. During the past few years a number of marine geodetic projects have either been planned or embarked upon by various organizations within both the public and private sectors. This article gives a brief review of the Norwegian projects which have special relevance to marine geodesy; this includes the following areas: recommendations, requirements, precision navigation, satellite positioning, reference systems, boundary problems, bathymetry, geological mapping, marine geoid determination, and data base developments. The reference list will give the reader more detailed sources of information.     

Caveats on tomographic images

Geological and geodynamic models of the mantle often rely on joint interpretations of published seismic tomography images and petrological/geochemical data. This approach tends to neglect the fundamental limitations of, and uncertainties in, seismic tomography results. These limitations and uncertainties involve theory, correcting for the crust, the lack of rays throughout much of the mantle, the difficulty in obtaining the true strength of anomalies, choice of what background model to subtract to reveal anomalies, and what cross‐sections to select for publication. The aim of this review is to provide a relatively non‐technical summary of the most important of these problems, collected together in a single paper, and presented in a form accessible to non‐seismologists. Appreciation of these issues is essential if final geodynamic models are to be robust, and required by the scientific observations.     

Pulse profile stability of the Crab pulsar

We present an X-ray timing analysis of the Crab pulsar, PSR B0531+21, using archival RXTE data. We have investigated the stability of the Crab pulse profile, in soft (2-20 keV) and hard (30-100 keV) X-ray energies, over the last decade of RXTE operation. The analysis includes measurement of the separation between the two pulse peaks and the intensity and widths of the two peaks. We did not find any significant time dependency in the pulse shape. The two peaks have been stable in phase, intensity and width f...     

Influence from Surrounding Land on the Turbulence Measurements Above a Lake

Turbulence measurements taken at a Swedish lake are analyzed. Although the measurements took place over a relatively large lake with several km of undisturbed fetch, the turbulence structure was found to be highly influenced by the surrounding land during daytime. Variance spectra of both horizontal velocity and scalars during both unstable and stable stratification displayed a low frequency peak. The energy at lower frequencies showed a daily variation, increasing in the morning and decreasing in the afternoon. This behaviour is explained by spectral lag, where the low frequency energy due to large eddies that originate from the convective boundary layer above the surrounding land. When the air is advected over the lake the small eddies rapidly equilibrate with the new surface forcing. However, the large eddies remain for an appreciable distance and influence the turbulence in the developing lake boundary layer. The variances of the horizontal velocity and scalars are increased by these large eddies, while the turbulent fluxes are mainly unaffected. The drag coefficient, Stanton number and Dalton number used to parametrize the momentum flux, heat flux and latent heat flux respectively all compare well with current parametrizations developed for open sea conditions. The diurnal cycle of the partial pressure of methane, $p\mathrm{CH}_{4}$ , observed at this site is closely related to the diurnal cycle of the lake-air methane flux. An idealized two-dimensional model simulation of the boundary layer at a lake site indicates that the strong response of $p\mathrm{CH}_{4}$ to the surface methane flux is due to the shallow internal boundary layer that develops above the lake, allowing methane to accumulate in a relatively small volume.     

Innovating the IPCC review process—the potential of young talent

There is significant potential in young talent for enhancing the credibility of the scientific assessments such as the IPCC’s by contributing to quality assurance and quality control. In this essay, we reflect on an experiment that was done by the Dutch government as part of its government review of a contribution to the IPCC’s Fifth Assessment Report (AR5). In an effort to review the entire Working Group II contribution to the AR5 within the official review period for the Second Order Draft (SOD), the PBL Netherlands Environmental Assessment Agency turned to PhD students. This article shows that a systematic review focusing on transparency and errors of a large scientific assessment document using young talented scientists can be successful if certain conditions are met. The reviewers need to have intrinsic motivation to conduct the review. There needs to be a communication plan that fosters engagement and a clear methodology to guide the reviewers through their task. Based on this experiment in review, we reflect on the wider potential for openness and crowdsourcing in scientific assessment processes such as the IPCC’s.     

Weibull-k Revisited: “Tall” Profiles and Height Variation of Wind Statistics

The Weibull distribution is commonly used to describe climatological wind-speed distributions in the atmospheric boundary layer. While vertical profiles of mean wind speed in the atmospheric boundary layer have received significant attention, the variation of the shape of the wind distribution with height is less understood. Previously we derived a probabilistic model based on similarity theory for calculating the effects of stability and planetary boundary-layer depth upon long-term mean wind profiles. However, some applications (e.g. wind energy estimation) require the Weibull shape parameter (k), as well as mean wind speed. Towards the aim of improving predictions of the Weibull- \(k\) profile, we develop expressions for the profile of long-term variance of wind speed, including a method extending our probabilistic wind-profile theory; together these two profiles lead to a profile of Weibull-shape parameter. Further, an alternate model for the vertical profile of Weibull shape parameter is made, improving upon a basis set forth by Wieringa (Boundary-Layer Meteorol, 1989, Vol. 47, 85–110), and connecting with a newly-corrected corollary of the perturbed geostrophic-drag theory of Troen and Petersen (European Wind Atlas, 1989, Risø National Laboratory, Roskilde). Comparing the models for Weibull-k profiles, a new interpretation and explanation is given for the vertical variation of the shape of wind-speed distributions. Results of the modelling are shown for a number of sites, with a discussion of the models’ efficacy and applicability. The latter includes a comparative evaluation of Wieringa-type empirical models and perturbed-geostrophic forms with regard to surface-layer behaviour, as well as for heights where climatological wind-speed variability is not dominated by surface effects.