A deep stratospheric intrusion event down to the earth’s surface of the megacity of Athens

This case study investigates a stratospheric intrusion event down to the earth’s surface (near sea-level pressure) of the greater area of Athens (23.43°E 37.58°N), which occurred on 9 October 2003 and caused a remarkable increase in surface ozone concentrations not related to photochemical production. This event is among the rare case studies investigating, on the one hand, a deep stratospheric intrusion down to the earth’s surface at near sea-level pressure and, on the other, an event affecting the near surface ozone of a megacity such as Athens. The synoptic situation is described by a deep upper lever trough at 300 and 500 hPa extending over Greece, which is related to a deep tropopause fold as revealed by vertical cross sections of potential vorticity, relative humidity, divergence and vertical velocity. The analysis of potential vorticity at several isentropic levels indicates a hook-shaped streamer of high PV values (greater than 4 pvu at the 315 K isentropic level) over southeast Europe, which coincides with a streamer of dry air as observed from satellite images of water vapor. The aforementioned structure characterizes a textbook case study of stratosphere-to-troposphere transport. The Lagrangian particle dispersion model FLEXPART was used to calculate the trajectories of air particles reaching the receptor site and the fraction of particles with stratospheric origin. It reveals an important direct stratospheric impact within 1 day related to the tropopause fold described in this study with the fraction of stratospheric particles reaching maximum values of 1.9 and 4.5% for threshold values of the dynamical tropopause 2 and 1.5 pvu, respectively. Furthermore, a larger indirect aged stratospheric contribution is also revealed 4 to 5 days prior to the release, related to stratospheric intrusion events at the western Atlantic Ocean, reaching maximum values of 2.5 and 6.9% of particles crossing the 2 and 1.5 pvu potential vorticity surfaces, respectively.     

IMAGES OF MAPS: A ROTATION EXPERIMENT*

Theories which explain mental imagery are discussed and are related to cognitive maps. An experiment was conducted to illustrate that people can code information about maps as visual images and use map images for a map-reading task. Subjects were shown maps which were rotated at various angles from north-at-the-top. The time needed to decide if a map was a correct or mirror representation was recorded. The results support the notion that people did this task by forming and rotating map images.     

Volume integrals of the products of spherical harmonics and their application to viscous dissipation phenomena in fluids

The equations governing the conversion of kinetic energy into heat in moving viscous media are formulated as volume integrals of products of spherical harmonics. Although the formulation of the fundamental equations is classical, difficulties in the integration of certain products of generalized spherical harmonics over a sphere have permitted heretofore the treatment of only two cases. The closed, form evaluation of eight fundamental types of definite integrals of the product of spherical harmonics, some of them new, or at least missing in the literature, makes possible for the first time the evaluation of these volume integrals in closed form for arbitrary order and index. Explicit details are given for the rates of energy dissipation produced by viscous motions characterized by spheroidal as well as toroidal symmetry.     

Objective climatology of 500-hPa cyclones in central and east mediterranean region during warm-dry period of the year

Summary ¶An Objective 500-hPa cyclone detection and analysis is performed during the warm-dry period (16 April to 15 October) of the year for the Central and Eastern Mediterranean Region (30°N–50°N, 5°E–35°E). The 40-year NCEP/NCAR reanalyzes gridded data of geopotential height and temperature employed in the study, enable a climatic approach with a spatial (2.5°×2.5°) and a 6-hour temporal (00, 06, 12, 18 UTC) resolution. The occurrence frequency for the entire region shows a high interannual variability without significant trends. The frequency maximization over land in the middle of the warm period indicates a possible relationship with land-air temperature difference. Three primary activity centers (Turkey, Black Sea and Genoa) are objectively determined in the frequency domain as local maxima and their intensity is assessed in terms of average geopotential height and temperature values. The Turkey center, though the most frequent, consists of shallow lows in contrast to the Black Sea center, which is second in frequency, but on average, contains the deepest lows amongst the three. The Genoa center, which comes third in frequency, shows the highest variability in the intensity of the lows. Frequency distributions in the area, during the three sub periods (Early, Middle and Late Warm Period) and during the four synoptic hours, provide insight in to the origins of these systems at the three locations and reveal secondary centers, such as the centers in the Adriatic (at 18 UTC), Northern Greece (during Middle Warm Period) and the South Aegean Sea (during Late Warm Period).Received February 20, 2002; revised November 4, 2002; accepted January 16, 2003 Published online July 30, 2003     

Stratigraphy of the mid-Holocene black bands in Lakes Michigan and Huron: Evidence for possible basin-wide anoxia

The post-glacial history of the Great Lakes has involved several changes in lake levels throughout the latest Pleistocene and Holocene, resulting from the changing position of the retreating Laurentide ice sheet, outlet incision and isostatic rebound. The final lowering of lake levels occurred at approximately 7600 ¹⁴C yr BP, after which lake levels began to rise again to the Nipissing highstand at approximately 4700 ¹⁴C yr BP. During this time of rising lake levels, black bands of iron sulfide were being formed in the sediments of all five of the Great Lakes. These bands signify suboxic to anoxic conditions, at least within the sediments and possibly at the sediment-water interface, during the middle Holocene warm interval. During this interval, the climate was warmer and drier than present, possibly resulting in the occasional absence of seasonal turnover in the lakes. We examined a series of piston cores from northern Lakes Michigan and Huron and found that the black bands are correlatable among cores taken from within the same basin. The observation that the banding can be correlated suggests a basin-wide cause, near-bottom or sub-bottom anoxia in the northern Michigan and northern Huron sediments during the mid-Holocene warm period. The sedimentary and geochemical processes in the Great Lakes during the middle Holocene warm interval are good indicators of possible future scenarios for the lakes as a result of global warming, as 21^st-century temperatures are predicted to reach similar levels due to increased concentrations of greenhouse gases.     

Evaluating trophic status and restoration procedures of a polluted lake,Lake Kastoria,Greece

Lake Kastoria is a shallow lake with many anthropogenic activities concentrated in its catchment area. Surficial runoff rich in agricultural waste and underground seepage from urban and rural areas enrich the lake with nutrients intensifying the eutrophication problem of the water.Restoration techniques, with different approach, each one are proposed to restore the lake water. Treatment with alum is very effective but needs special care during the application. Reeds harvesting is an inexpensive and effective way and in combination with the city sewage redirection will improve the water quality and the trophic status of the lake sufficiently.     

Genetic implications of minor-element and Sr-isotope geochemistry of alkaline rock complexes in the Wet Mountains area,Fremont and Custer counties,Colorado

Concentrations of Rb, Sr, and REE (rare earth elements), and Sr-isotopic ratios in rocks of the Cambrian alkaline complexes in the Wet Mountains area, Colorado, show that rocks formed as end-products of a variety of magmas generated from different source materials. The complexes generally contain a bimodal suite of cumulus mafic-ultramafic rocks and younger leucocratic rocks that include nepheline syenite and hornblende-biotite syenite in the McClure Mountain Complex, nepheline syenite pegmatite in the Gem Park Complex, and quartz syenite in the complex at Democrat Creek. The nepheline syenite and hornblende-biotite syenite at McClure Mountain (535±5m.y.) are older than the syenitic rocks at Democrat Creek (511±8m.y.). REE concentrations indicate that the nepheline syenite at McClure Mountain cannot be derived from the hornblende-biotite syenite, which it intrudes, or from the associated mafic-ultramafic rocks. REE also indicate that mafic-ultramafic rocks at McClure Mountain have a source distinct from that of the mafic-ultramafic rocks at Democrat Creek.In the McClure Mountain Complex, initial⁸⁷Sr/⁸⁶Sr ratios for mafic-ultramafic rocks (0.7046±0.0002) are similar to those of hornblende-biotite syenite (0.7045±0.0002), suggesting a similar magmatic source, whereas ratios for carbonatites (0.7038±0.0002) are similar to those of nepheline syenite (0.7038±0.0002). At Democrat Creek, initial ratios of syenitic rocks (0.7032±0.0002) and mafic-ultramafic rocks (0.7028±0.0002) are different from those of corresponding rocks at McClure Mountain.     

The dynamics of conservative mixing in estuaries

Mixing plots, in which a dissolved constituent is plotted against salinity or chlorinity, are commonly used to interpret conservative and non-conservative processes in estuarine systems. A bend in the resulting curve is generally interpreted as indicative of the reactive or non-conservative nature of the constituent or the presence of multiple sources or sinks within the estuary. This paper demonstrates analytically that bends in mixing curves may also result from temporal variations in end-member (river or ocean) constituent concentrations even for conservative constituents. A one-dimensional dispersion equation is used to calculate the distribution of salinity and a conservative constituent in a model estuary. Both straight and bent mixing curves are shown resulting simply from changing the variability of the river constituent concentration. For no variability the curve is straight. For variability with a period much less than the flushing time, the average curve for a general data set straight, whereas the curve for a synoptic data set is bent. For variability with a period greater than the flushing time a bent curve results. Since bent mixing curves can occur for conservative properties, the use of these curves for interpretation of estuarine processes must be undertaken with an understanding of the temporal variability of the river and ocean constituents and their relationship to the estuary mixing properties and flushing time.     

Petrochemistry of the Fish Cove rhyolite,Keweenaw peninsula,Michigan, U.S.A.

A small (360 × 180 m) rhyolitic intrusive body in the lower portion of the Portage Lake Lava Series of Michigan's Keweenaw peninsula was mapped and sampled in detail. The rhyolite is one of a number of similar bodies which make up less than 1% of the total volume of this thick Late-Precambrian plateau basalt pile. The rock is a low-calcium rhyolite with fine-grained homogeneous texture and sparse phenocrysts of plagioclase and quartz. Analyses of selected trace and major elements for 21 samples taken from the body reveal a chemical zonation consisting of a core zone enriched in K, Rb and Ba, and a border zone relatively poor in these elements. Little areal difference is found with respect to other elements tested (Mn, Sr, Zr, Ca, Ti, and Fe). This apparently primary zonation seems to result from the migration of K, Rb and Ba during crystallization of the shallow intrusive. Though zoned, the trace-element chemistry of the Fish Cove body is distinct from that of eight other rhyolites in the Portage Lake Lava Series, and suggests that fingerprinting by trace elements might be a fruitful method for identifying and correlating the sources of numerous rhyolitic pebbles in conglomerates interbedded with the basaltlava flows of the Portage Lake Series.