Principal Components Analysis of Rainfall and Associated Synoptic Models of the Southwest Monsoon over India

Summary  The summer monsoon circulation shows various spatial and temporal oscillations and often a combination of systems produces an integrated effect. In this study phases of the southwest (SW) monsoon have been identified in an objective manner with the help of T-mode principal component analysis (PCA) of weekly rainfall anomalies. Mean composite charts have been prepared utilising all available upper air data (1977–1986) for each category of the SW monsoon epochs identified by the PCA. These sets of charts have been constructed for both the strong and weak phases associated with the first four significant principal components (PCs). A well defined east-west oriented trough system, extending from about 28° N Latitude/65° E Longitude to 20° N Latitude/90° E Longitude, in the lower levels, has been the main feature associated with the strong phase of the monsoon corresponding to PC I. The trough in the lower levels is more marked in the eastern half compared to the western half in both the sets of charts associated with strong phases of the monsoon related to the PC II and PC III. With PC II, the position of the troughs in the lower levels is further north of its location in PC III. The east-west trough system associated with the strong phase of PC IV has a large southward tilt with height. The charts corresponding to the weak phases of these PCs have synoptic features, such as the position of the trough close to the foothills of the Himalayas, and the shifting of middle and upper tropospheric anticyclones to the south. The study suggests an objective method of interpretation of principal components by utilising synoptic data. In addition, synoptic models and data sets corresponding to different phases of the monsoon can also be prepared in an objective manner by such PCA. Received July 18, 1997 Revised April 30, 1999     

Arsenic anomalies in shallow Venetian Plain (Northeast Italy) groundwater

A pilot area within the Venetian Plain was selected to assess the arsenic (As) contamination of groundwater. The area represents a typical residential, industrial and agricultural organization representative of most western countries, and is also devoid of lithologies with high or anomalous As content. Hydrogeological and chemical data have been collected, the latter spatialized by a geostatistical approach. The unconfined aquifer reservoir varies from a predominantly gravel composition in the north to a sandy and silt–clay composition further south, including peat layers. The hydrochemical features of the waters are rather homogeneous, featuring low mineral content and a Ca-bicarbonate signature. In contrast, the redox state is highly variable; oxidizing conditions are predominant in the northern and coarse parts of the aquifer, whereas reducing potentials prevail in the southern and silt–clay parts. Several well waters contain arsenic in excess of drinkable limits (=10 ppb), and most of these wells are located in the southern area. A large portion of the studied area has a high probability of containing non-potable water (up to 150 ppb As). Remarkably, As “hot spots” (As > 300 ppb, up to 431 ppb) were identified at the transition from gravel to silt–clay sediments. No industrial or agricultural source of As has been found.     

Alteration processes in the CV chondrite parent body based on analysis of NWA 2086 meteorite

Analysis of the NWA 2086 CV3 chondrite showed a matrix/chondrule ratio of 52%, similar to Bali, Mokoia, and Grosanaja. Nearly twice as many chondrule fragments as intact ones demonstrate that an early fragmentation phase occurred prior to final accretion. After this event, no substantial mechanical change or redeposition is evident. Rims with double‐layered structures were identified around some chondrules, which, in at least one case, is attributed to an accretionary origin. The rim's outer parts with a diffuse appearance were formed by in situ chemical alteration. During this later process, Mg content decreased, Fe content increased, and olivine composition was homogenized, producing a rim composition close to that of the matrix. This alteration occasionally happened along fractures and at confined locations, and was probably produced by fluid interactions. Iron oxides are the best candidate for a small grain‐sized alteration product; however, technical limitations in the available equipment did not allow exact phase identification. These results suggest that NWA 2086 came from a location (possible more deeply buried) in the CV parent body than Mokoia or Bali, and suffered less impact effects—although there is no evidence of sustained thermal alteration. This meteorite may represent a sample of the CV parent asteroid interior and provide a useful basis for comparison with other CV meteorites in the future.     

Space-time interaction amongst clusters of mining induced seismicity

Elementary cluster analysis of induced seismicity in a South African gold mine has shown that there is a clear interaction amongst the clusters; and that the level of the interaction is a function of the distance. The clusering algorithm used is an adaptation of the single-link cluster analysis which considers both three-dimensional space and time. A high level of interaction between the clusters is demonstrated from the cross-correlation analysis of seismic activity rates and radiated energy. A distinct decrease in the value of correlation coefficients was detectable as distance increased. This was somewhat surprising, considering the simplicity of the technique used. Since no attempt is made to study the physical mechanisms of interaction, these results are very preliminary, but interesting from an observational point of view.     

VERTICAL SEISMIC PROFILING IN COAL*

The intellection of seismic wave propagation in coal measures demands direct observation of the wavefield progression. Two vertical seismic profiles with high spatial and temporal sampling, were recently recorded in the Sydney Basin coalfields as part of an experimental coal seismic program. Static corrections and interval velocities were obtained by an automated system to determine first kicks and pulse rise times. Upgoing and downgoing waves were separated in the f—k-plane using a novel technique of contour slice filtering. The isolated upgoing waves clearly display reflections from the major coal seams within the stratigraphic sequence. The downgoing wave spectra were subjected to attenuation analysis. The deduced specific quality factor Q for Permian coal measure rocks lies in the range 20–70. Similar estimates were obtained in the time domain from measurements of pulse broadening. Synthetic VSP seismograms, computed using an exact recursive formulation, are an indispensable aid to interpretation. They illustrate the filtering effects of coal seams and sequences, and the effects of the contribution of internal and free-surface multiple reflections in the recorded wavetrains.     

Saturn's electrostatic discharges: Could lightning be the cause?

It is proposed that Saturn's electrostatic discharges (SED) might be generated in the planet's equatorial atmosphere, perhaps as lightning from a storm system. The 10^h10^m periodicity of the signal envelope duplicates that of Saturn's equatorial jet. The rings shield the atmosphere from solar EUV photons, and thereby substantially reduce the local ionospheric cutoff frequency to allow low-frequency SED to leak out. Many of the unusual properties of SED could be explained in terms of changes in the storm system, the relative spacecraft position in the beaming pattern of the source, local refraction of the signal by the highly disturbed ionosphere, and the influence of the ring particles on the highest frequency component of SED. A comparison of SED with planetary lightning on other planets shows that the two are similar in general character and some time behavior; the power output of SED may be higher than most planetary lightnings but that is unclear because of uncertainties in the measurements and variations in the signal's spectrum. Our simple discussion suggests that lightning could be a viable source for SED and that exotic ring mechanisms are not necessarily required.     

CLIMAP SSTs re-revisited

Since the 1976 publication of the CLIMAP ice age sea surface temperature (SST) reconstruction showing a 1–2 ^∘C tropical cooling a substantial debate has arisen as to whether tropical SSTs may instead have been 4–5^∘ colder than present. Herein I review the arguments for large SST variations and question a number of key findings, particularly the validity of ice-age coral SST estimates and “down-projecting” tropical snowline changes to the surface. GCM results indicate that an intermediate solution requiring ∼2.5 ^∘C warm pool cooling is consistent with most quantitative low elevation surface land data and is small enough to allow the persistence of tropical biota in the ocean during glacial times. The proposal reduces estimated ice-age climate sensitivity (for a doubling of CO₂) from a “high-end” sensitivity of about 4.5 ^∘C (for a 5–6 ^∘C tropical cooling) to a “mid-range” sensitivity of about 3.0 ^∘C for a 2.5 ^∘C warm-pool decrease. Received: 28 July 1999 /Accepted: 12 August 1999     

Phytoplankton diversity and chlorophyll-A in a polluted estuary

The quantity of phytoplankton in Newark Bay, New Jersey as indicated by chlorophyll-a content of the water, is low in the winter and early spring, and fluctuates greatly during the spring and summer. Chlorophyll-a concentrations are generally less than 20 μg/l until April. Between April and August, three phytoplankton blooms were indicated by chlorophyll-a concentrations as high as 81.4 μg/l. Net phytoplankton diversity values indicated generally eutrophic conditions; however, there was no significant correlation between diversity and chlorophyll-a concentrations. A role of nannoplankton in blooms is indicated.     

Models of travel demand with endogenous preference change and heterogeneous agents

In the literatures of regional science, urban economics, and urban development planning, a working assumption is that individuals respond to incentives and regulations, given their preferences. Models for planning and policy analyses are used to consider what might occur if the incentives or regulations were different. In these models, however, preferences are usually assumed to be given and stable, and agents are usually assumed to be homogeneous. This paper focuses on the implications of making preferences in models of policy implementation endogenously determined and time varying heterogeneous agents. We consider first the recent literature on intertemporal choice and preference change, which cuts across many disciplines, and more briefly the literature on norm-regarding behavior. We then elaborate a simple model of transportation demand—from a static to a dynamic orientation, from fixed and exogenously given preferences of strictly self-regarding agents to endogenously determined and policy-induced preferences of heterogeneous agents—and illustrate its characteristics with simple numerical examples.