Structure function characteristics for 2 metre temperature and relative humidity in different horizontal resolutions

The isotropic correlations of forecast errors in the HIRLAM system are investigated for different horizontal grid sizes in order to achieve an improved representation of the structure functions for high-resolution surface analysis. The investigation is performed for 2 metre temperature and relative humidity and makes use of operational forecasts from DMI-HIRLAM at the Danish Meteorological Institute (DMI), which can support the background for a surface analysis in three different horizontal resolutions. Two different well-known methods for determining isotropic forecast error correlations are applied. The first method compares forecasts to observations (the Observation Method), while the second makes use of two different forecasts valid for the same time (the NMC Method). The latter method is also used to investigate isotropy as well as the influence of land–sea contrast and orography. A comparison of the two mentioned methods reveals a good correspondence between them, and the investigation of monthly changes shows some seasonal tendencies. The isotropy assumption is shown to be acceptable to a first approximation, despite a slight dependency on the predominant flow. The results further suggest a decrease in the background error correlation scales when going to higher horizontal resolution in the forecast model.     

Characterization, lateral variability and lateral extent of discontinuity surfaces on a Carbonate Platform (Barremian to Lower Aptian, Oman)

Hiati of various duration in carbonates are commonly expressed as discontinuity surfaces. The understanding of processes that form and affect these surfaces leads to an improved sequence-stratigraphic interpretation, a reliable outcrop correlation, and better models for reservoir compartmentalization. Various intraformational discontinuities were analysed and interpreted in a well-exposed study window, 2·5 km in lateral length and 60 m in height comprising the Barremian-Aptian Qishn Formation (Haushi-Huqf area, central Oman). This study focuses on the lateral extent and morphology of the surfaces, the petrography of the underlying rocks, and the facies changes and geochemical trends across these discontinuities. Furthermore, the lateral variability of discontinuity surfaces was documented. Three genetic types of discontinuities are differentiated: (i) erosion surfaces; (ii) omission surfaces (hard- and firmgrounds); and (iii) composite surfaces with evidence for both subaerial exposure and submarine boring. Field observations, combined with petrographic and geochemical data, suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea-level fluctuations of regional scale. In contrast, a large number of laterally limited surfaces (<1 km) are related to locally active processes such as waves and current erosion. The lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity, the sea-floor topography, waves and currents and differential erosion. The most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment. This variability is caused by spatial variability in the tidal flat environment, meteoric alteration and differential erosion. This study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces. This variability must be kept in mind when interpretations and correlations are based on one-dimensional sections or cores.