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In this paper, a statistical study on geoeffectiveness of CMEs integrated with DH-type II radio bursts, association of Dst with plasma and interplanetary field parameters (T,V,P,β,Bz,Bt,E) and their product function BzV for solar cycle 24 is presented. We have selected 119 DH-CME events from March 2008 to December 2015. Based on minimum Dst index ≤−50 nT of geo­magnetic storm, the events are assorted into two groups, specifically (i) Geoeffective events (ii) Non-geoeffective events. The geoeffective events are found to have high start frequency, low end frequency, broad bandwidth, long duration, slower drift rate than non-geoeffective events. CME speed and flare flux for geoeffective events are moderately correlated(r=0.50) which shows that flares may be related to geomagnetic storms through CMEs. Higher speed of CMEs associated with geoeffective events suggests that CME speed is an important pa­rameter for geoeffectiveness. A large fraction of CME associated with DH-type-II radio bursts are linked with geomagnetic storm which again indicates that CMEs accompanied by DH-type-II radio bursts are effectively responsible for producing geomagnetic storms. A good correlation of Dst with BzV(r>0.5) reflects that interplanetary field and plasma parameters also play an important role in the occurence of geomagnetic storms.

The study of the solar energetic particle events (SEPs) and their association with solar flares and other activities are very crucial to understand the space weather. Keeping this in view, in this paper, we present the study of the SEPs (intensity equal to or greater than 10 pfu) during the solar cycle 21 to 24 (1976-2017) in > 10 MeV energy channels associated with solar flares. For our analysis, we have used the data from different instruments onboard SOHO satellite. We have examined the flare size, source location, CMEs characteristics of associated SEPs. About 31% and 69% of the SEPs were originated from the eastern and western solar hemisphere respectively. The average CME speed and width were 1238 km/s and 253 deg respectively. About 58 % SEPs were associated with halo CMEs and 42% of SEPs associated with CMEs width varying from 10 deg to 250 deg respectively., 17 pages, 6 figures (accepted for the publication in Journal of Astrophysics and Astronomy)

We present here a study of Solar Energetic Particle Events (SEPs) associated with solar flares during 2010–2014 in solar cycle 24. We have selected the flare events (≥GOES M-class), which produced SEPs. The SEPs are classified into three categories i.e. weak (proton intensity ≤ 1 pfu), minor (1 pfu

This paper presents a statistical analysis of different parameters responsible for the geoeffectiveness of solar eruptions during the rising phase of solar cycle 24. We have selected 33 halo CME events from the beginning of the current solar cycle 24 (2009–2013). The levels of geomagnetic activity are categorized into two groups based on the observed minimum Dst index, i.e., moderate (−100 nT

North-south asymmetry has been a significant aspect exhibited by various solar activity parameters of the Sun. In this work we have statistically analyzed soft X-ray (SXR) flares during the period Jan 1981 to Dec 2016 for four different solar cycles (SCs) covering cycles 21, 22, 23 and 24. We have presented the class wise (B, C, M & X) variation of SXR flares for these SCs. SXR flare activity is lowest in solar cycle 24 as compared to cycles 22 and 23. It is shown that M class activity continuously decreased from SC 21 to 24. X and C class flares show higher activity in SC 22 and 23 as compared to SC 24, whereas B class flare activity is higher for SC 23. We have also studied the north-south (N-S) asymmetry of SXR flares for SCs 21, 22, 23 and 24. Our study revealed that during SCs 21, 22 and 23 the flare activity was more pronounced in the Southern hemisphere. However, the flare activity was equally distributed between the northern and southern hemispheres for SC 24

In the present paper, we have studied the statistical analysis between all India homogeneous rainfall (RF) with sunspot number (SN) during 1900-2014 (115-year period). We have calculated correlations coefficient of rainfall with sunspot number (SN) for annual and seasonal months: January, February (JF); March April May (MAM); June July August September (JJAS) and October November December (OND) and we have obtained high correlation ranging between 0.75 to 0.95. Our results show that rainfall is strongly influenced by sunspot number. Our study also indicates that occurrence of solar activity features play an important role for variability of rainfall.

Statistical analysis of rainfall pattern and its variability for 20 years (1990-2010) data is performed for two mountainous urban centres of Uttarakhand i.e. Almora (29.60 N, 79.670 E and altitude 1,204m asl) and Nainital (29.40 N, 79.470 E and altitude 2,020m asl). Non Parametric method of Principal Component Analysis (PCA) gives the correlation between different extreme rainfall indices. It is concluded that PCA suggest 90% of the variance in composite matrix of extreme rainfall indices.

Using 30 years data (1986-2015) we have made an attempt to study the dependency of total column ozone (TCO) on solar activity features: solar flares (SF), solar active prominence (SAP) and sunspot numbers (SN) for two hill stations of Uttarakhand viz. Nainital (29.40 N.79.470E) and Mussorie (30.270 N 78.060 E) by Artificial neural network (ANN) technique. Our study supports the fact that solar activity features contribute to the production of ozone.

The analysis of rainfall pattern and indices of extreme rainfall events is performed for two meteorological stations located in the Central Himalayan Region which is highly vulnerable to rain-induced hazards. The records of these rain-induced disasters suggest that such events are generally observed in later part of monsoon season, when soil is saturated after monsoon rains. An attempt is made here to test trends of 19 different extreme rainfall indices that have been widely used in the literature, using daily rainfall data for two urban centres (Nainital and Almora) over the period 1992–2005. We have used statistical tools such as Sen’s method and Mann–Kendall test for detection of trend in annual rainfall, monsoon rainfall, number of rainy days and 1-day extreme rainfall. Principal component analysis gives the correlation between different extreme rainfall indices. Time series of principal components are representing the trends of extreme indices, their variation and interrelation between different indices. The perception study conducted in the same sites indicates that extreme rainfall events and change in rainfall amount and timing are well perceived by the local people.

The present study is an attempt to analyse the precipitable water vapour (PWV) derived from Global Positioning System (GPS) and observed meteorological data over Almora, Central Himalayan Region. The PWV values derived using GPS study is compared with the corresponding moderate resolution imaging spectro-radiometer (MODIS) data. The statistical analysis reveals a positive correlation between both methods. Moderate resolution imaging spectroradiometer near-infrared (MODIS NIR) clear column water vapour product shows a higher correlation (R 2 = 90–93 %) with GPS-derived precipitable water vapour on annual scale as compared to the seasonal scale (R 2 = 62–87 %). MODIS is found to be overestimating in NIR clear column where the magnitude of bias and RMSE show systematic changes from season to season. Monsoon is an important phenomenon in the Indian weather context and holds significant importance in Central Himalayan ecosystem. The monthly and seasonal variation in precipitable water vapour is related with monsoon onset in the region. Diurnal variations in precipitable water vapour are studied with other meteorological data over Almora during dry and wet season. The precipitable water vapour had minimum value in the morning, increases in the afternoon to evening and again decreases to the midnight in both the dry and wet seasons. These results suggest that diurnal variation of water vapour is caused by the transport of water vapour by thermally induced local circulation.

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 B 2 V) 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 B 2 V, 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.

This paper presents the study of normalized north–south asymmetry, cumulative normalized north–south asymmetry and cumulative difference indices of sunspot areas, solar active prominences (at total, low (⩽40°) and high (⩾50°) latitudes) and Hα solar flares from 1964 to 2008 spanning the solar cycles 20–23. Three different statistical methods are used to obtain the asymmetric behavior of different solar activity features. Hemispherical distribution of activity features shows the dominance of activities in northern hemisphere for solar cycle 20 and in southern hemisphere for solar cycles 21–23 excluding solar active prominences at high latitudes. Cumulative difference index of solar activity features in each solar cycle is observed at the maximum of the respective solar cycle suggesting a cyclic behavior of approximately one solar cycle length. Asymmetric behavior of all activity features except solar active prominences at high latitudes hints at the long term periodic trend of eight solar cycles. North–south asymmetries of SAP (H) express the specific behavior of solar activity at high solar latitudes and its behavior in long-time scale is distinctly opposite to those of other activity features. Our results show that in most cases the asymmetry is statistically highly significant meaning thereby that the asymmetries are real features in the N–S distribution of solar activity features.

Regular and systematic measurements of mesospheric temperatures have been carried out during March and April 2007 to determine planetary-scale wave activities in the tropical region, utilizing ground-based Rayleigh Light Detection and Ranging (LiDAR) and satellite-based Microwave Limb Sounder (MLS) data from Gadanki, India (13.5° N, 79.2° E) and MLS data over a site in North America (23.5° N, 100° W). A dominant component of the 3-5 day period wave is revealed at four altitudes (80, 70, 60 and 50 km) over the two observation stations. The estimated vertical wavelength (∼40 km), zonal phase speed (∼140 m s-1), longitudinal and latitudinal extensions have suggested the wave to be an ultra-fast Kelvin (UFK) wave with zonal wave number 1. In addition to the UFK wave, a probable quasi 2 day Rossby gravity wave is also found to be present most of the time. Another 5-7 day wave component, observed at some altitudes with significant prominence, is surmised to be a manifestation of a 6.5 day wave.

In the present study, the non-linear solar radiation models for predicting the monthly average daily diffuse radiation are developed using the measured data on global radiation, diffuse radiation and sunshine hours for 12 locations of India. Statistical method is used to derive these correlations. The developed models are employed to estimate the monthly average daily diffuse radiation. The performance of these correlations is compared with existing model. Accuracy of developed relationships is also tested using statistical indicators viz. Percentage error (PE), root mean square error (RMSE), mean percentage error (MPE) and mean bias error (MBE). The study finds that these statistical parameters have very low values for the proposed models. A cubic correlation of diffuse coefficient with percent possible sunshine gives the best fit. The maximum values of RMSE, MPE and MBE for the proposed third order equation are 4.33%, 8.68% and −1.25% respectively while in the case of existing model these values are 13.28%, 13.39% and −3.83% respectively. Hence, it is possible to apply the cubic equation for the prediction of monthly mean daily diffuse radiation.

A statistical study of different solar activity features (sunspot number, solar active prominences and Hα solar flares) with all India homogeneous rainfall (RF) is presented using 44 years (1963–2006) data. The correlation coefficient, significance of correlation coefficient and other statistical parameters are computed for the seasonal months of January–February (JF), March–April–May (MAM), June–July–August–September (JJAS), October–November–December (OND) and also annual. Correlation coefficient and its significance of two, four and six point moving average of RF with different solar activity features have also been calculated. A negative correlation is found between annual RF and solar activity features, and for sunspot number and solar flares with two, four and six point moving average of RF whereas moves from negative to positive for solar active prominences. Lag/lead analysis between RF and different solar activity features have also been analyzed and presented.

A study on North South (NS) asymmetry of different solar activity features (DSAF) such as solar proton events, solar active prominences, H alpha flare index, soft X ray flares, monthly mean sunspot area and monthly mean sunspot number were carried out from 1996 to 2008. It is found in our result that solar cycle 23 is magnetically weak compared to solar cycle 22. Study shows the Southern dominance of DSAF during the time period of study. During the rising phase of the cycle the numbers of DSAF approximately equal on the North and South Hemisphere. However, these activities tend to shift from Northern Hemisphere to Southern Hemisphere in between year 1998 to 1999. The statistical significance of the asymmetry time series using a chi square test of goodness of fit indicates that in most of the cases the asymmetry is highly significant, i.e., the asymmetry is a real feature in the NS distribution of DSAF., Comment: In this manuscript total 19 pages including 7 figures and 3 tables

Extensive measurement of middle atmospheric temperature with the help of lidar data of more than 10 years (1998–2008) and TIMED/SABER data of 7 years (2002–2008), has been carried out from a low latitude station, Gadanki, India (13.5° N, 79.2° E), which exhibits the presence of semiannual oscillation (SAO) and annual oscillation (AnO). The AnO component is stronger in the mesospheric region (80–90 km) and the SAO is dominant at stratospheric altitudes (30–50 km). Overall, the AnO possesses higher amplitude ~6–7 K, and the SAO shows less amplitude ~1–2 K. The AnO present at 90 km finds crest near summer solstice, and the same at 80 km shows peak near winter solstice with a downward progression speed ~1.7 km/month. The SAO propagates downward with an average phase speed ~9 km/month and phase maximizes around equinox and solstice at 50 and 30 km, respectively. The observed SAO has also shown seasonal asymmetry in peaks.

Enhancement of Sm3+ emission has been observed as a result of non-radiative energy transfer from optically excited UO2++ in zinc phosphate glass. The study is primarily done by observing the decrease in UO2++ emission with varying Sm3+ concentration. The energy transfer mechanism is found to be mainly electric dipole–dipole in nature. Transfer probabilities efficiencies and average donor–acceptor distances have been calculated.

[1] A novel measurement of seasonal variability of the middle atmospheric thermal structure has been carried out by comparing ground-based lidar and space-based TIMED/SABER observations from a low-latitude station, Gadanki (13.5°N, 79.2°E), India. Lidar temperature has been cross-verified by retrieving from Cooperative Institute for Research in the Atmosphere's (CIRA) CIRA-86 model and SABER observation density and pressure values independently. Observed results are also compared with CIRA-86 model data. Model data show significant difference with observed ones. Observed results match nicely among themselves throughout the year, which further validates the SABER data at low latitude with an average deviation of ∼2 K in 35–75 km altitude range with respect to the Rayleigh lidar. Seasonal pattern of adiabatic lapse rate all over the altitude range reveals a statically stable atmosphere during the observation period. Stratopause temperature shows semiannual oscillation (SAO) in seasonal pattern of variation, which matches with previous observations from low-latitude stations.

This paper presents a statistical analysis of Soft X-ray (SXR) flares during the period January 1976 to December 2007 covering solar cycles (SCs) 21, 22, and 23. We have analysed north-south (N-S) and east-west (E-W) asymmetry of SXR at low (less than equal to 40 degree), high (greater than equal to 50 degree) and total latitudes and center meridian distances (CMDs) respectively. We have also presented the N-S and E-W asymmetry of different intensity classes (B, C, M, and X) during the period of investigation. A slight southern and eastern excess is found after analysis during SC 21, 22, and 23. We found that the annual N-S and E-W hemispheric asymmetry at low latitudes and CMDs is the same as total latitudes and CMDs respectively. E-W asymmetry is different at low and high CMDs. Our statistical result shows that N-S asymmetry is statistically more significant than E-W asymmetry. Total SXR flare activity during SC 23 is high compared to SC 21 and 22. The B class flare activity is higher for SC 23 where as C, M and X class activities are higher for SC 21. We have also analysied the flare evolution parameters, i.e. duration, rise time, decay time and event asymmetry for total SXR as well as for different classes for last three SCs. The duration, rise time and decay time increase with increasing intensity class. On analysing event asymmetry indices, we found more positive values during SC 21 (64.86 per cent) and SC 22 (54.31 per cent), but for SC 23 we have more negative values (48.08 per cent). Our study shows that during SC 23 we have more SXR flare events having shorter decay time as compared to SC 21 and SC 22., 22 Pages, 14 figures, submitted to New Astronmy Journal

In this paper we present the results of a study of the spatial distribution and asymmetry of solar active prominences (SAP) for the period 1996-2007 (solar cycle 23). For more meaningful statistical analysis we have analysed the distribution and asymmetry of SAP in two subdivisions viz. Group1 (ADF, APR, DSF, CRN, CAP) and Group2 (AFS, ASR, BSD, BSL, DSD, SPY, LPS). The north-south (N-S) latitudinal distribution shows that the SAP events are most prolific in the 21-30degree slice in the northern and southern hemispheres and east-west (E-W) longitudinal distribution study shows that the SAP events are most prolific (best visible) in the 81-90degree slice in the eastern and western hemispheres. It has been found that the SAP activity during this cycle is low compared to previous solar cycles. The present study indicates that during the rising phase of the cycle the number of SAP events were roughly equal on the north and south hemispheres. However, activity on the southern hemisphere has been dominant since 1999. Our statistical study shows that the N-S asymmetry is more significant then the E-W asymmetry., 21 pages 5 figures; Published online; 02 October, 2009; Solar Physics Journal