Neoproterozoic siliciclastic sedimentation around Kampa-Tenpa area,Pranhita Godavari Graben (PGG), Central India: Facies analysis,petrography and depositional environment

The Pranhita-Godavari Graben (PGG) represents a major lineament in south Indian Peninsular cratonic province, which preserves a thick column of sediments. In geological time scale, these sedimentary units correspond to Mesoproterozoic to Mesozoic period. The Mesoproterozoic sedimentation has been confined mainly to southern part of the PGG, while Neoproterozoic sediments are exposed at northern tip of the graben. In the area of investigation siliciclastic sedimentation units are exposed, wherein five major lithofacies have been marked out. These lithofacies are i) breccia (Br), ii) large scale trough cross-bedded sandstone (Ls), iii) small-scale trough cross-bedded sandstone (Sss), iv) horizontal bedded sandstone (Hs) and v) ripple laminated sandstone (Rs). The amalgamation of these lithofacies strongly divulges that the lower part of the succession was deposited in braided-streams, whereas the upper part was deposited in erg environment. The unimodal paleocurrent is evident in lower part of the succession while bimodal paleocurrent is noticed from sandstones at upper part of the succession. In general, the sandstones exhibit northwesterly paleocurrent direction. The petrographic studies point out that the sandstones are arenites and were deposited in interior type of continental block provenance under semi-arid to hot humid palaeoclimate. The high percentage of floating grains and the low percentage of interpenetrative contacts as well as the low value of contact index for these sandstones divulge that the grains did not suffer much compaction thereby pointing to shallow burial. The sub-angular zircon and tourmaline suggest that these minerals have travelled short distance from the source rocks. The high percentage of garnet and presence of epidote, staurolite, sillimanite, zoisite, amphibole and kyanite indicate that the sediments were derived from the nearby metamorphic source rocks.     

Relationship between interplanetary field/plasma parameters with geomagnetic indices and their behavior during intense geomagnetic storms

This paper presents a correlative study between the peak values of geomagnetic activity indices (Dst, Kp, ap and AE) and the peak values of various interplanetary field (Bt, Bz, E and σ_B) and plasma (T, D, V, P and β) parameters along with their various products (BV, BzV and B²V) during intense geomagnetic storms (GMSs) for rising, maximum and decay phases as well as for complete solar cycle 23. The study leads to the conclusion that the peak values of different geomagnetic activity indices are in good correlation with Bt, Bz, σ_B, V, E, BV, BzV and B²V, therefore these parameters are most useful for predicting GMSs and substorms. These parameters are also reliable indicators of the strength of GMSs. We have also presented the lag/lead time analysis between the maximum of Dst and peak values of geomagnetic activity indices, various interplanetary field/plasma parameters for all GMSs. We have found that the average of peak values of geomagnetic activity indices and various field/plasma parameters are larger in decay phase compare to rising and maximum phases of cycle 23. Our analyses show that average values of lag/lead time lie in the ≈?4.00 h interval for Kp, ap and AE indices as well as for Bt, Bz, σ_B, E, D and P. For a more meaningful analysis we have also presented the above study for two different groups G1 (CME-driven GMSs) and G2 (CIR-driven GMSs) separately. Correlation coefficients between various interplanetary field/plasma parameters, their various products and geomagnetic activity indices for G1 and G2 groups show different nature. Three GMSs and associated solar sources observed during three different phases of this solar cycle have also been studied and it is found that GMSs are associated with large flares, halo CMEs and their active regions are close to the solar equator.     

A new method for estimation of near surface specific humidity over global oceans

Summary A new methodology for deriving daily averages of near surface specific humidity (Q _a ) is developed. Remotely sensed parameters, total water vapor (W), boundary-layer water vapor (W _b ), and sea-surface temperature (SST) are used to derive Q _a . Genetic algorithm (GA) is used to find the empirical function relating the input (W, W _b , and SST) and output (Q _a ) parameters. The input data consist of 2 years (1999–2000) of daily W, W _b , from SSM/I (Special Sensor Microwave Imager), and SST data from AVHRR (Advanced Very High Resolution Radiometer). COADS (Comprehensive Ocean Atmospheric Data Set) observations of Q _a are used to develop and evaluate the new methodology. The performance of the algorithm is measured with COADS observations, which are not used in the development phase. The global mean rms error for daily averages Q _a is 1.5 ± 0.40 g/kg. Slightly higher discrepancies between Q _a derived from the new method and COADS observations are found over the Northwestern Pacific, North Atlantic oceans and Arabian Sea. This method improves upon the humidity retrieval of Liu (1986), Schulz et al (1993), and Chou et al (1997).