Performance assessment of three convective parameterization schemes in WRF for downscaling summer rainfall over South Africa

Austral summer rainfall over the period 1991/1992 to 2010/2011 was dynamically downscaled by the weather research and forecasting (WRF) model at 9 km resolution for South Africa. Lateral boundary conditions for WRF were provided from the European Centre for medium-range weather (ECMWF) reanalysis (ERA) interim data. The model biases for the rainfall were evaluated over the South Africa as a whole and its nine provinces separately by employing three different convective parameterization schemes, namely the (1) Kain–Fritsch (KF), (2) Betts–Miller–Janjic (BMJ) and (3) Grell–Devenyi ensemble (GDE) schemes. All three schemes have generated positive rainfall biases over South Africa, with the KF scheme producing the largest biases and mean absolute errors. Only the BMJ scheme could reproduce the intensity of rainfall anomalies, and also exhibited the highest correlation with observed interannual summer rainfall variability. In the KF scheme, a significantly high amount of moisture was transported from the tropics into South Africa. The vertical thermodynamic profiles show that the KF scheme has caused low level moisture convergence, due to the highly unstable atmosphere, and hence contributed to the widespread positive biases of rainfall. The negative bias in moisture, along with a stable atmosphere and negative biases of vertical velocity simulated by the GDE scheme resulted in negative rainfall biases, especially over the Limpopo Province. In terms of rain rate, the KF scheme generated the lowest number of low rain rates and the maximum number of moderate to high rain rates associated with more convective unstable environment. KF and GDE schemes overestimated the convective rain and underestimated the stratiform rain. However, the simulated convective and stratiform rain with BMJ scheme is in more agreement with the observations. This study also documents the performance of regional model in downscaling the large scale climate mode such as El Niño Southern Oscillation (ENSO) and subtropical dipole modes. The correlations between the simulated area averaged rainfalls over South Africa and Nino3.4 index were ?0.66, ?0.69 and ?0.49 with KF, BMJ and GDE scheme respectively as compared to the observed correlation of ?0.57. The model could reproduce the observed ENSO-South Africa rainfall relationship and could successfully simulate three wet (dry) years that are associated with La Niña (El Niño) and the BMJ scheme is closest to the observed variability. Also, the model showed good skill in simulating the excess rainfall over South Africa that is associated with positive subtropical Indian Ocean Dipole for the DJF season 2005/2006.     

Period–luminosity relations for red supergiant variables – I.The calibration

We present CCD photometry of red supergiant long-period variables (LPVs) in the Per OB1 association, the Large Magellanic Cloud (LMC) and M33. The photometry was obtained in the Kron–Cousins R and I bandpasses and in a narrow bandpass ( λ ₀=8250 Å, FWHM=300 Å) chosen to avoid TiO bands in the spectral energy distribution of the LPVs. Because the strength of the TiO bands varies greatly with temperature, which varies with the phase of an LPV, avoiding TiO reduces the amplitude of the photometric variations seen in LPVs. The result is a lower dispersion and a well defined period–luminosity (PL) relation.
For the LMC sample we find an rms dispersion of 0.27 mag in the narrow-band PL relation and slightly larger dispersions for the LPVs in Per OB1 and M33. This dispersion is comparable to that of the Cepheid PL relation at similar wavelengths. Adopting a distance modulus of 18.5±0.1 mag for the LMC, we obtain distance moduli of 11.68±0.15 mag for Per OB1 and 24.85±0.13 mag for M33. These distances agree well with those based on main sequence fitting for Per OB1 and the Cepheid distance for M33. Since LPVs are ∼ 5 times more common than Cepheids and have a well defined PL relation, LPVs provide a promising method for estimating Galactic and extra galactic distances.     

Late Quaternary sea‐level change and evolution of Belfast Lough,Northern Ireland: new offshore evidence and implications for sea‐level reconstruction

The interplay of eustatic and isostatic factors causes complex relative sea‐level (RSL) histories, particularly in paraglacial settings. In this context the past record of RSL is important in understanding ice‐sheet history, earth rheology and resulting glacio‐isostatic adjustment. Field data to develop sea‐level reconstructions are often limited to shallow depths and uncertainty exists as to the veracity of modelled sea‐level curves. We use seismic stratigraphy, 39 vibrocores and 26 radiocarbon dates to investigate the deglacial history of Belfast Lough, Northern Ireland, and reconstruct past RSL. A typical sequence of till, glacimarine and Holocene sediments is preserved. Two sea‐level lowstands (both max. ?40 m) are recorded at c. 13.5 and 11.5k cal a bp . Each is followed by a rapid transgression and subsequent periods of RSL stability. The first transgression coincides temporally with a late stage of Meltwater Pulse 1a and the RSL stability occurred between c. 13.0 and c. 12.2k cal a bp (Younger Dryas). The second still/slowstand occurred between c. 10.3 and c. 11.5k cal a bp . Our data provide constraints on the direction and timing of RSL change during deglaciation. Application of the Depth of Closure concept adds an error term to sea‐level reconstructions based on seismic stratigraphic reconstructions.     

2.5-D DC Resistivity Modeling Considering Flexibility and Accuracy

We highlighted the flexibility of using unstructured mesh together with the local refinement by a resistivity model with complicated topography. The effect of topography is emphasized. Based on this, we calculated a specific class of layered models and found that the accuracy is not always satisfactory by utilizing the standard approach. As an improvement, we employed the layered earth as the reference model to calculate the wavenumbers. The comparison demonstrates that the accuracy is considerably improved...     

The Development of Laser Ablation ICP-MS and Calibration Strategies: Examples from the Analysis of Trace Elements in Volcanic Glass Shards and Sulfide Minerals

This contribution presents a review of the recent developments in laser ablation inductively coupled plasma-mass spectrometry. We describe the important developments which have occurred in the laser systems used, leading to a spatial resolution of around 20 (im, and give an overview of the major instrument developments which have affected the geological applications of laser ablation ICP-MS. We describe the calibration of laser ablation for the analysis of trace elements in two different matrices: volcanic glass shards and sulfide minerals. We show how single glass shards can be analysed using the National Institute of Standards and Technology (NIST) glass certified reference materials for calibration and demonstrate the effect of using single spot analyses compared to rastering of the calibration sample. We show the importance of inter-shard variation and demonstrate that averaged single shard analyses produce data which compare well with bulk analyses. The calibration of the laser system for sulfide mineral analysis is discussed and two different strategies are proposed, one using spiked pressed powder pellets of sulfides and the other metal reference materials. We present conclusions and recommendations for the calibration of laser ablation ICP-MS instruments.     

Potassium‐argon dates from the Arltunga Nappe complex,northern territory

Twenty‐four mineral separates from the Arunta Complex, four from the metamorphosed Heavitree Quartzite (White Range Quartzite), and one whole rock sample of metamorphosed Bitter Springs Formation, all from the western part of the White Range Nappe of the Arltunga Nappe Complex, and two samples from the autochthonous basement west of the nappe have been dated by the K‐Ar method. The samples from the basement rocks form two groups. Those in the southern or frontal part of the nappe are of Middle Proterozoic (Carpentarian) age (1660–1368 m.y.), determined on hornblende, biotite, and muscovite. In the northern or rear part of the nappe, all but one of the muscovite samples and two biotites are of Middle Silurian to Early Carboniferous age (431–345 m.y.); the remainder of the biotite dates range from 1775 to 548 m.y. (including the two samples from the autochthon), and two hornblendes gave dates of 1639 and 2132 m.y. respectively. All the muscovite samples from the Heavitree Quartzite, and the whole rock sample from the Bitter Springs Formation gave Early to Middle Carboniferous dates (358–322 m.y.). The findings support the identification of the White Range Quartzite as the metamorphosed part of the Heavitree Quartzite, which in turn supports the interpretation of the structure of the area as a large, basement‐cored fold nappe. In addition, they date the time of the Alice Springs Orogeny as pre‐Late Carboniferous, which agrees with fossil evidence from elsewhere in the area. The Alice Springs Orogeny was accompanied by widespread greenschist facies meta‐morphism that progressively metamorphosed the Heavitree Quartzite and Bitter Springs Formation, and retrogressively metamorphosed the Arunta Complex. However, the basement rocks in the southern part of the nappe escaped this metamorphism and retain a Middle Proterozoic age, thus dating the time of the Arunta Orogeny in this region as Carpentarian or older.     

Computer-composite mapping for geologists

A computer program for overlaying maps has been tested and evaluated as a means for producing geologic derivative maps. Four maps of the Sugar House Quadrangle, Utah, were combined, using the Multi-Scale Data Analysis and Mapping Program, in a single composite map that shows the relative stability of the land surface during earthquakes. Computer-composite mapping can provide geologists with a powerful analytical tool and a flexible graphic display technique. Digitized map units can be shown singly, grouped with different units from the same map, or combined with units from other source maps to produce composite maps. The mapping program permits the user to assign various values to the map units and to specify symbology for the final map. Because of its flexible storage, easy manipulation, and capabilities of graphic output, the composite-mapping technique can readily be applied to mapping projects in sedimentary and crystalline terranes, as well as to maps showing mineral resource potential.     

The use of MODIS data to derive acreage estimations for larger fields: A case study in the south-western Rostov region of Russia

Recent developments in remote sensing technology, in particular improved spatial and temporal resolution, open new possibilities for estimating crop acreage over larger areas. Remotely sensed data allow in some cases the estimation of crop acreage statistics independently of sub-national survey statistics, which are sometimes biased and incomplete. This work focuses on the use of MODIS data acquired in 2001/2002 over the Rostov Oblast in Russia, by the Azov Sea. The region is characterised by large agricultural fields of around 75 ha on average. This paper presents a methodology to estimate crop acreage using the MODIS 16-day composite NDVI product. Particular emphasis is placed on a good quality crop mask and a good quality validation dataset. In order to have a second dataset which can be used for cross-checking the MODIS classification a Landsat ETM time series for four different dates in the season of 2002 was acquired and classified. We attempted to distinguish five different crop types and achieved satisfactory and good results for winter crops. Three hundred and sixty fields were identified to be suitable for the training and validation of the MODIS classification using a maximum likelihood classification. A novel method based on a pure pixel field sampling is introduced. This novel method is compared with the traditional hard classification of mixed pixels and was found to be superior.     

Assessing Seasonal Transport and Deposition of Agricultural Emissions in Eastern North Carolina, U.S.A.

— There is an increasing interest regarding the fate of nitrogenous compounds emitted from agricultural activities in the southeastern United States. Varying climate, topography and proximity to the Atlantic Ocean particularly complicates the problem. An increased understanding of the interaction of synoptic scale flow with mesoscale circulations would constitute a significant improvement in the assessment of regional scale transport and deposition potential. This knowledge is necessary to facilitate current and future modeling attempts in the region as well as for planning future monitoring sites to develop a cohesive regional policy for the abatement strategies. The eastern portion of North Carolina is used as a case example due to its high, localized emission of nitrogen compounds from agricultural waste. Three periods: July 2–7, 1998, October 5–11, 1998, and December 12–19, 1998, corresponding to three different seasons were studied. Surface wind and thermodynamic patterns were analyzed using surface observing stations and archived-model analysis results centered over eastern North Carolina. Diurnal and seasonal patterns were identified for dispersion and concentration values obtained using an air pollution transport and dispersion model. This mesoscale information was used to draw qualitative conclusions regarding the possible trends and deviations in the dynamic trajectories as well as the resulting near-surface concentrations and deposition potential in eastern North Carolina. Results show that highly variable seasonal and diurnal atmospheric circulations characterize the study domain. These variations can significantly impact the transport and fate of pollutants released in this region. Generally, summer provides the highest potential for localized deposition, while fall can provide opportunity for long-range transport. The results also suggest that mean climatological or seasonally averaged flow patterns may not be sufficient for analyzing the fate of the agricultural releases in this region. At the very least, mean and variance based analysis is required to capture the climatology of the dispersion and deposition patterns. These patterns in eastern North Carolina appear to be sensitive to the strength and location of air mass boundaries along the coastal plain, indicating diverse scale interactions affecting the variability and uncertainty in the regional pollutant transport.     

Comparison of Brewer spectrophotometer ultraviolet data from similar latitudes in the Northern and Southern Hemisphere

This paper presents UV data recorded over 12 months in 2000/2001 at a southern hemisphere (Toowoomba) and similar latitude northern hemisphere (BigBend and Everglades) sites using Brewer Spectrophotometers. The peak daily erythemally weighted UV (DUV) at the Toowoomba site was 8.8% and 25% higher compared to that at the BigBend and Everglades sites, respectively. The Everglades site exposures are lower than the BigBend site exposures in summer and spring. This may be due to the higher cloud cover for the Everglades site. The summer DUV values between Toowoomba and BigBend are similar. In spring, the average DUV value is the greatest at BigBend compared to the other two sites. Results indicate that variability between the measurement sites is due to varying cloud and ozone, and possibly due to aerosol and airmass differences of each region. Of these different site-specific local atmospheric conditions, cloud was the main contributor to the differences in UV between the sites.