Wind field analysis using unit-vector density mapping

Summary An automated mapping technique, termed unit-vector density mapping (UVDM), is introduced as a method of displaying continuous instantaneous wind velocities and other vector quantities. The purpose of introducing this technique is to 1) generate renewed interest in meteorological data display techniques and 2) address specific concerns in the display and interpretation of vector quantities of particular interest to meteorologists. With this graphic procedure, the density of short standard-length line segments (unit-vectors) represents wind speed and unit-vector orientation show wind direction. This paper describes the plotting algorithms for producing UVDM maps and compares this technique to existing procedures for mapping wind vectors.

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Zusammenfassung Eine automatisierte kartographische Technik — genannt Unit-Vector Density Mapping (UVDM) — wird als Methode zur kontinuierlichen Darstellung der momentanen Windgeschwindigkeiten und anderer vektoriellen Größen im Bestreben vorgestellt, zum einen vermehrt Interesse auf die Darstellungstechniken meteorologischer Daten zu lenken und zum anderen, um einige speziell für Meteorologen relevante Bereiche der Darstellung und Interpretation von vektoriellen Größen hervorzuheben. Bei der genannten graphischen Vorgangsweise zeigt die Dichte der Einheitsvektoren die Windgeschwindigkeit an, während die Richtung der Einheitsvektoren die Windrichtung angibt. Vorliegende Studie beschreibt die Zeichenroutinen zur Herstellung von UVDM-Karten und vergleicht diese Technik mit vorhandenen Darstellungsmethoden von Windvektoren.

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With 9 Figures     

Cosmic ray flux impact on clouds? An analysis of radiosonde, cloud cover, and surface temperature records from the United States

Summary ¶Many scientists have suggested that variations in cosmic ray flux may impact cloudiness at regional, hemispheric, or global scales. However, considerable debate surrounds (a) whether high or low clouds are most strongly impacted by cosmic rays, (b) the degree of seasonality in cloud responses to cosmic rays, and (c) the determination of physical processes involved in cosmic ray/cloud interactions. Some scientists find strong correlation coefficients between cloud measurements and cosmic ray flux, while others find no relationship whatsoever; virtually all scientists working on this issue are hampered by the relatively short time period with accurate cloud and cosmic ray flux records. In an attempt to extend the period of record, we assembled surface and radiosonde data for the United States over the period 1957–1996 along with sunspot records which are known to be strongly, but inversely, related to cosmic ray flux. We also assembled cloud cover data and cosmic ray measurements over a reduced time period. We found that periods with low sunspot number (times with high cosmic ray flux) are associated with significantly higher dew point depressions, a higher diurnal temperature range, and less cloud cover. Our results do not support suggestions of increased cloud cover during periods of high cosmic ray flux.Received May 14, 2002; accepted February 17, 2003 Published online May 26, 2003     

The Cosmic Foreground Explorer (COFE): A balloon-borne microwave polarimeter to characterize polarized foregrounds

The COsmic Foreground Explorer (COFE) is a balloon-borne microwave polarimeter designed to measure the low-frequency and low-ℓ characteristics of dominant diffuse polarized foregrounds. Short duration balloon flights from the Northern and Southern Hemispheres will allow the telescope to cover up to 80% of the sky with an expected sensitivity per pixel better than 100 μK/deg² from 10 GHz to 20 GHz. This is an important effort toward characterizing the polarized foregrounds for future CMB experiments, in particular the ones that aim to detect primordial gravity wave signatures in the CMB polarization angular power spectrum.     

Horizontal and seasonal patterns of tropical zooplankton from the eutrophic Prado Reservoir (Colombia)

Zooplankton community analyses can reveal valuable information about the trophic status and secondary production in reservoirs. The zooplankton seasonal distribution and important physical and chemical parameters in Prado Reservoir (Tolima, Central Colombia) were studied in monthly surveys throughout a hydrological cycle (February 2000-January 2001) in order to establish seasonal patterns and the biotic and abiotic relationships for the reservoir. Surface zooplankton collections at 1 m depth were taken at six sampling stations with regard to reservoir morphometry, location of main tributaries and mixing areas of the incoming tributaries. Cladocerans numerically dominated (48.1%) the community throughout the study period followed by Copepoda (32.7%), Rotifera (19.1%), and Diptera larvae (0.01%). Among the cladocerans, there was a greater abundance of Bosmina longirostris (69.8%) than other crustaceans. Among the Rotifera, Brachionus falcatus was the most abundant with 23% and Keratella tropica was least abundant with 8%. The only cyclopoid species found was Thermocyclops decipiens. The phantom midge Chaoborus sp. was also part of the zooplankton community. Based on numbers, cladocerans represented a significant component of the zooplankton in both dry and rainy seasons. Four species (Brachionus spp., K. tropica, Diaphanosoma brachyurum, Ceriodaphnia cornuta, Moina sp., and T. decipiens) had never previously been found in the reservoir, but were recorded for other standing Colombian water bodies. The replacement of B. longirostris instead of Daphnia sp. as dominant species was observed. The results of the comparison of the different studies confirmed that the trophic state of this artificial lake may be classified as eutrophic, and in general, physical, and chemical homogeneity were observed both spatially and temporally.     

Age of the Corsica–Sardinia rotation and Liguro–Provençal Basin spreading: new paleomagnetic and Ar/Ar evidence

The age of spreading of the Liguro–Provençal Basin is still poorly constrained due to the lack of boreholes penetrating the whole sedimentary sequence above the oceanic crust and the lack of a clear magnetic anomaly pattern. In the past, a consensus developed over a fast (20.5–19 Ma) spreading event, relying on old paleomagnetic data from Oligo–Miocene Sardinian volcanics showing a drift-related 30° counterclockwise (CCW) rotation. Here we report new paleomagnetic data from a 10-m-thick lower–middle Miocene marine sedimentary sequence from southwestern Sardinia. Ar/Ar dating of two volcanoclastic levels in the lower part of the sequence yields ages of 18.94±0.13 and 19.20±0.12 Ma (lower–mid Burdigalian). Sedimentary strata below the upper volcanic level document a 23.3±4.6° CCW rotation with respect to Europe, while younger strata rapidly evolve to null rotation values. A recent magnetic overprint can be excluded by several lines of evidence, particularly by the significant difference between the in situ paleomagnetic and geocentric axial dipole (GAD) field directions. In both the rotated and unrotated part of the section, only normal polarity directions were obtained. As the global magnetic polarity time scale (MPTS) documents several geomagnetic reversals in the Burdigalian, a continuous sedimentary record would imply that (unrealistically) the whole documented rotation occurred in few thousands years only. We conclude that the section contains one (or more) hiatus(es), and that the minimum age of the unrotated sediments above the volcanic levels is unconstrained. Typical back-arc basin spreading rates translate to a duration ≥3 Ma for the opening of the Liguro–Provençal Basin. Thus, spreading and rotation of Corsica–Sardinia ended no earlier than 16 Ma (early Langhian). A 16–19 Ma, spreading is corroborated by other evidences, such as the age of the breakup unconformity in Sardinia, the age of igneous rocks dredged west of Corsica, the heat flow in the Liguro–Provençal Basin, and recent paleomagnetic data from Sardinian sediments and volcanics. Since Corsica was still rotating/drifting eastward at 16 Ma, it presumably induced significant shortening to the east, in the Apennine belt. Therefore, the lower Miocene extensional basins in the northern Tyrrhenian Sea and margins can be interpreted as synorogenic “intra-wedge” basins due to the thickening and collapse of the northern Apennine wedge.     

Supraglacial Debris Supply in the Cuerpo de Hombre paleoglacier (Spanish Central System): Reconstruction and Interpretation of a Rock Avalanche Event

During the deglaciation stages of the last glacial period a rock avalanche took place on the glacier that occupied the upper sector of the Cuerpo de Hombre Valley (Sierra de Béjar). The material displaced during the avalanche fell onto the ice, was transported by the glacier and later deposited as supraglacial ablation till. The cause of the avalanche was the decompression of the valley slopes after they were freed from the glacier ice (stress relaxation). Reconstruction of the ice masses has been carried out to quantify the stress relaxation that produced the collapse. The rock avalanche took place on a lithologically homogeneous slope with a dense fracture network. The avalanche left a 0.4 ha scar on the slope with a volume of displaced material of 623 ± 15 × 10³ m³. The deposit is an accumulation of large, angular, heterometric boulders (1–100 m³ in volume) with a coarse pebble‐size matrix. The avalanche can be explained as a relaxation process. This implies rock decompression once the glacier retreat left the wall ice free (debuttressing). Calculations show that the avalanche took place where the decompression stresses were highest (130–170 kPa). In the Spanish Central System paleoglaciers the largest accumulation of morainic deposits occurred after the glacial maximum and the earliest stages of the ice retreat. The process described here is used as an example to formulate a hypothesis that the largest accumulations of tills were formed in relation to enhanced slope dynamics once some glacier retreat had occurred.     

Bela oceanic lithosphere assemblage and its relation to the Réunion hotspot

The Bela ophiolite of Pakistan contains a complete ophiolite-accretionary wedge-trench sequence emplaced onto the Indian continental margin during the northward drift of India-Seychelles over the active Réunion hotspot. A structurally higher ophiolite overlies an accretionary prism, which is thrust over a foreland basin. Shear-sense determinations in peridotite mylonites in the ophiolite footwall and imbrication structures in the underlying accretionary wedge indicate an ESE emplacement. Sedimentary rocks in the accretionary wedge indicate Aptian-Albian pillow lavas, initially deep water conditions, and increasing influence from the continent until the Maastrichtian. The ophiolite emplacement was predated and accompanied by Fe-tholeiitic and alkaline magmatism related to the Réunion hotspot and continuous incorporation of trench sediments into the accretionary wedge. ³⁹Ar/⁴⁰Ar dating shows that the ophiolite formed around 70 Ma. Intraoceanic subduction initiated between 70 and 65 Ma, obduction onto the Indian passive margin occurred during the formation of the Deccan traps at ≈ 66 Ma, and final thrusting onto the continental margin ended in the early Eocene (≈ 50 Ma). The ophiolite emplacement occurred during the counterclockwise separation of Madagascar and India-Seychelles which caused shortening and consumption of oceanic lithosphere between the African-Arabian and the Indian-Seychelles plates.     

TEMPORAL STATISTICS: AN APPLICATION IN SNOWFALL CLIMATOLOGY

A method is introduced for the analysis of temporal distributions of climatic data based on a comparison of a variable's frequency distribution in the time dimension to a standard bell-shaped curve through time. The following statistics are defined using mean monthly snowfall data: the temporal mean, which is the average time for accumulation of 50% of the annual snowfall total; the temporal standard deviation, which characterizes the mean annual spread of snowfall accumulation about the mean; temporal skewness, which characterizes the symmetry of the annual snowfall distribution; temporal kurtosis, which measures the peakedness of the annual distribution; and temporal correlation, which quantifies the degree of association between two temporal distributions. Analysis of snowfall data demonstrates the utility of temporal statistics for quantifying temporal and geographic variations in a climatic variable's seasonal distribution. [Key words: snowfall, climatology, temporal statistics.]