We report the results of the South Indian Strain Measuring Experiment (SISME) designed to determine whether strain related to microseismicity in the past century may have deformed the networks of the 19th century Great Trigonometrical Survey of India (GTS). More than a dozen GTS points were measured between Mangalore, Madras, and Kanyakumari in southernmost India using GPS geodesy to determine regional deformation. Detailed measurements were made near two of the original baselines of the survey to determine the reliability of dilatational strain data for the network. The regional measurements revealed negligible regional dilatational (+ 11.2 + 10 microstrain) and shear strain changes (0.66± 1.2μradians) in the southernmost 530 km of India. In addition to these measurements, we determined the rate of northward and eastward motion of a point in Bangalore (1991–1994) in the ITRF92 reference frame to be 39 ± 3.5 mm/year, and 51 ± 11 mm/year respectively. This is consistent with NUVEL-1A plate motion estimate for India. Simultaneous measurements to a point near Kathmandu reveal that the Indian plate and the Southern Himalaya are moving approximately in unison, placing an upper limit on the rate of creep processes beneath the lesser Himalaya of ≈6 mm/year, and suggesting relatively rigid behavior of the Indian plate north of Bangalore. The stability of the Indian plate is confirmed by the absence of significant changes in the lengths of the two baselines at Bangalore and Cape Comorin, which, within the limits of experimental error have not changed since 1869. The measurements place an upper limit for recent deformation in the southern peninsula, and hence a lower limit for the renewal time for intraplate earthquakes in the region of approximately 10,000 years, assuming shear failure strain of approximately 100 μradians. This, in turn, implies that recurrence intervals for Peninsular Earthquakes far exceed the length of the written historic record, suggesting that the characterisation of seismic recurrence intervals from historical studies is likely to be fruitless. In contrast, the SISME experiment demonstrates that the noise level of geodetic studies based on 19th century GTS data is less than 0.02 μstrain/year, providing considerable scope for delineating regions of anomalously high seismogenic strain, by GPS measurements at all available trig points of the 19th century GTS survey.

To investigate the temperature changes at 100 hPa over Indian region from Arabian Sea (AS) to Bay of Bengal (BOB), analysis is performed using Atmospheric Infra Red Sounder (AIRS) temperature and outgoing long-wave radiation (OLR) data of 9 years (2003–2011). Fine-scale temperature variations have been studied and shown for summer (March–April–May, MAM), summer monsoon (June–July–August–September, JJAS) and winter (November–December–January–February, NDJF) months. Similarities and differences in the latitudinal and longitudinal variation of temperature and the possible causes have been examined. During MAM and NDJF, the temperature increases latitudinally by ∼2–3 K and ∼4–5 K from 3.5° to 20.5°N, respectively. However, the temperature decreases by ∼2.0–2.5 K during JJAS. A similar contrasting behaviour is observed in latitudinal temperature gradient. For MAM and NDJF, the gradient decreases from ∼0.18 to ∼0.14 K/deg and ∼0.25 to ∼0.18 K/deg, respectively, as we move longitudinally from 60° to 90°E; however, for JJAS, it increases from ∼0.10 to ∼0.14 K/deg over the same longitudes. It is found that latitudinal temperature gradient for NDJF is larger by about a factor of 1.5. Analysis suggests latitudinal change in temperature occurs due to low OLR (proxy of convection) and its northward progression during summer monsoon. Correlation coefficient (𝑅_xy) between OLR and temperature is computed latitudinally (3.5° to 20.5°N) at different longitudes and during JJAS (monsoon months), 𝑅_xy is negative (∼−0.73) over 60° and 70°E longitudes, but it turns positive (∼0.92) over 80° and 90°E longitudes (which is convectively active region), suggesting a close association between low temperature and low OLR. Land–sea contrast is also observed in temperature at 100 hPa with a slight increase (∼0.5 K) from sea to land.