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Projected Changes in Semi Permanent Systems of Indian Summer Monsoon in CORDEX-SA Framework
Get PDFThe semi-permanent systems such as Seasonal Heat Low (HL), Monsoon Trough (MT), Tibetan Anticyclone (TA), Tropical Easterly Jet (TEJ) and Low Level Jet (LLJ) or Somali jet are observed over Indian region during Indian summer monsoon season (June through September). These systems play a vital role in defining the strength of the Indian summer monsoon rainfall as a whole. Here we evaluate the ability of Consortium for Small-Scale Modeling (COSMO) regional Climate Model (COSMO-CLM), a high resolution regional climate model within the Coordinated Regional Climate Downscaling Experiment for South Asia (CORDEX-SA) framework, to simulate these systems of Indian summer monsoon. The historical runs of the COSMO-CLM for the period 1951-2000 are analysed. Overall the COSMO-CLM is able to simulate these components reasonably well. Possible changes in the position and the strength of these systems and their role in changing rainfall pattern over India are examined to assess the impact of global warming, under the RCP 4.5 simulations towards the end of the century (2051-2100). The analysis shows that the semi permanent systems may not strengthen in the future as compared to the present climate. The summer monsoon rainfall does not show uniform changes over the region. It is likely to enhance over the southern parts of the country, south of 20?S while it is projected to decrease in the northern parts under the global warming scenario
Intra-seasonal variability of atmospheric CO2 concentrations over India during summer monsoons
No full textIn a study based on a data assimilation product of the terrestrial biospheric fluxes of CO2 over India, the subcontinent was hypothesized to be an anomalous source (sink) of CO2 during the active (break) spells of rain in the summer monsoon from June to September (Valsala et al., 2013). We test this hypothesis here by investigating intraseasonal variability in the atmospheric CO2 concentrations over India by utilizing a combination of ground-based and satellite observations and model outputs. The results show that the atmospheric CO2 concentration also varies in synchrony with the active and break spells of rainfall with amplitude of ±2 ppm which is above the instrumental uncertainty of the present day techniques of atmospheric CO2 measurements. The result is also consistent with the signs of the Net Ecosystem Exchange (NEE) flux anomalies estimated in our earlier work. The study thus offers the first observational affirmation of the above hypothesis although the data gap in the satellite measurements during monsoon season and the limited ground-based stations over India still leaves some uncertainty in the robust assertion of the hypothesis. The study highlights the need to capture these subtle variabilities and their responses to climate variability and change since it has implications for inverse estimates of terrestrial CO2 fluxes
Optimization of spectral bands for ocean colour remote sensing of aquatic environments
No full textSelection of central wavelengths, bandwidths and the number of spectral bands of any sensor to be flown on a remote sensing satellite is important to ensure discriminability of targets and adequate signal-to-noise ratio for the retrieval of parameters. In recent years, a large number of spectral measurements over a wide variety of water types in the Arabian Sea and the Bay of Bengal have been carried out through various ship cruises. It was felt pertinent to use this precious data set to arrive at meaningful selection of spectral bands and their bandwidths of the ocean colour sensor to be flown on the forthcoming Oceansat-3 of ISRO. According to IOOCG reports and studies by Lee and Carder (2002) it is better for a sensor to have ~15 bands in the 400-800 nm range for adequate derivation of major properties (phytoplankton biomass, colored dissolved organic matter, suspended sediments, and bottom properties) in both oceanic and coastal environments from observation of water colo
What controls seasonal evolution of sea surface temperature in the Bay of Bengal?: Mixed layer heat budget analysis using moored buoy observations along 90°E
Get PDFContinuous time-series measurements of near surface meteorological and ocean variables obtained from Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) moorings at 15°N, 90°E; 12°N, 90°E; and 8°N, 90°E and an Ocean Moored buoy Network for Northern Indian Ocean (OMNI) mooring at 18°N, 90°E are used to improve understanding of air-sea interaction processes and mixed layer (ML) temperature variability in the Bay of Bengal (BoB) at seasonal time scales. Consistent with earlier studies, this analysis reveals that net surface heat flux primarily controls the ML heat balance. The penetrative component of shortwave radiation plays a crucial role in the ML heat budget in the BoB, especially during the spring warming phase when the ML is thin. During winter and summer, vertical processes contribute significantly to the ML heat budget. During winter, the presence of a strong barrier layer and a temperature inversion (warmer water below the ML) leads to warming of the ML by entrainment of warm subsurface water into the ML. During summer, the barrier layer is relatively weak, and the ML is warmer than the underlying water (i.e., no temperature inversion); hence, the entrainment cools the mixed layer. The contribution of horizontal advection to the ML heat budget is greatest during winter when it serves to warm the upper ocean. In general, the residual term in the ML heat budget equation is quite large during the ML cooling phase compared to the warming phase when the contribution from vertical heat flux is small
Impact of microphysics schemes in the simulation of cyclone hudhud using WRF-ARW model
Get PDFA Very Severe Cyclonic Strom (VSCS) "Hudhud" crossed Andhra coast near Visakhapatnam on 12th October 2014 and caused significant damage to property due to both wind and surge. In the present study, an attempt is made to simulate and test the capability of the state of art Advanced Research Weather Research and Forecasting (WRF-ARW) model in capturing the wind intensity and track of cyclone accurately. The simulation has been carried out using three domains with a horizontal resolution of 27 km for domain 1, 9 km for domain 2 and 3 km for domain 3. Multiple simulations using initial conditions (NCEP FNL) at an interval of 6 hours, same cumulus parameterization and time integration schemes but with different microphysics schemes are carried out. The main source of energy for tropical cyclone is the latent hear release (convective heating) in clouds, which depend on microphysical processes and the released dynamical properties. The objective of the present study is to find out the best microphysics for accurate simulation of intensity and track of tropical cyclone at high model domain resolution towards storm surge studies. The best performance was found for the model integrated for 48 hours starting from 10th October 2014 to 12th October 2014. Simulated features include (track, maximum sustained wind, sea level pressure and rainfall) were compared with IMD best track data and it was observed that simulations with WRF LIN microphysics scheme compare well with observations. Other synoptic features of rainfall was also simulated and discussed in relation to model performance. Overall this study gives emphasis on the studies towards sensitivity analysis of microphysics parameterization using WRF simulations at high model grid resolution (3 km) to imply towards storm surge applications in Bay of Bengal
Comparing the spatio-temporal variability of remotely sensed oceanographic parameters between the Arabian Sea and Bay of Bengal throughout a decade
Get PDFThe spatio-temporal variability of sea-surface temperature (SST), photosynthetically active radiation (PAR), chlorophyll-a (Chl-a), particulate organic carbon (POC) and particulate inorganic carbon (PIC) was evaluated in the Arabian Sea (ABS) and Bay of Bengal (BoB), from July 2002 to November 2014 by means of remotely sensed monthly composite Aqua MODIS level-3 data having a spatial resolution of 4.63 km. Throughout the time period under consideration, the surface waters of ABS (27.76 ± 1.12°C) were slightly cooler than BoB (28.93 ± 0.76°C); this was observed during all the seasons. On the contrary, the availability of PAR was higher in ABS (45.76 ± 3.41 mol m-2 d-1) compared to BoB (41.75 ± 3.75 mol m-2 d-1), and its spatial dynamics in the two basins was mainly regulated by cloud cover and turbidity of the water column. The magnitude and variability of Chl-a concentration were substantially higher in ABS (0.487 ± 0.984 mg m-3), compared to BoB (0.187 ± 0.243 mg m-3), and spatially higher values were observed near the coastal waters. Both POC and PIC exhibited higher magnitudes in ABS compared to BoB; however, the difference was substantially high in case of POC. None of the parameters showed any significant temporal trend during the 12-year span, except PIC, which exhibited a significant decreasing trend in ABS
Spatio-temporal evolution of chlorophyll-a in the Bay of Bengal: a remote sensing and bio-argo perspective
No full textArgo floats equipped with sensors to measure Dissolved Oxygen, Chlorophyll-a and backscattering are deployed in the Arabian Sea, Bay of Bengal and Southern Indian Ocean as part of Indian Argo program. In this study, abnormal chlorophyll-a bloom observed by a float with WMO ID 2902086 deployed in the south central Bay of Bengal is analyzed. High concentration of chlorophyll > 0.8 mg/l is observed during December 2013. This period is also associated with drop in temperature and increase in salinity. Analysis of data from the bio-Argo float has shown the impact of many cyclones and depressions that occurred during the period. Of particular importance is cyclone ‘Madi’, which passed very near to the position of mentioned float, during December 2013. This is also evident from the satellite based wind observations from OSCAT through curl of wind stress and Ekman pumping. The sub-surface chlorophyll bloom is substantiated by the surface chlorophyll-a values of MODIS during the period. Intense mixing caused due to the passage of cyclone might have resulted in mixing of subsurface waters thereby breaking the stratification of otherwise stable surface waters of Bay of Bengal, enhancing the nutrient supply, which resulted in strong chlorophyll bloom. The subsurface chlorophyll structure of Bay of Bengal and its variability during the passage of cyclone is for the first time revealed by the floats equipped with biological sensors. This work reveals the synergistic application of in-situ (Bio- Argo) and satellite data to monitor the changes in subsurface structure during the passage of cyclones
Interannual variability of upper ocean stratification in Bay of Bengal: observational and modeling aspects
No full textThe annual cycle and interannual variability of stratification in Bay of Bengal (BoB) are studied using both observations and Global Ocean Data Assimilation System (GODAS) analysis during 2003–2012. Annual cycle of stratification and sea surface temperature (SST) evolve coherently, highlighting its role on modulating air-sea interaction over this climatologically important region. Spatial distribution of stratification shows strong seasonality in ARGO observations, whereas it is highly underestimated in GODAS with highest discrepancies during fall and spring. The annual cycle of sea surface salinity (SSS) in GODAS is out of phase with observations implying potential feedbacks. During La Niña years, SSS drop in fall and winter and are lesser than those reported during El Niño years. All these features are misrepresented in GODAS. As stratification modulates air-sea interaction over BoB especially during El Niño and La Niña years, such misrepresentation of ocean stratification may lead to unrealistic thermocline-SST coupling in the models. The mean stratification and its interannual variability in GODAS are weaker than observed even though interannual variability in freshwater flux (P-E) is higher in GODAS. Detailed analysis of GODAS with in situ observations reveals that upper ocean current shear (vertical) is overestimated in GODAS, leading to unrealistically strong mixing which is primarily responsible for the deeper penetration of surface warm and freshwater resulting weaker stratification. As GODAS is used to initialize the ocean component of the coupled forecasting system for seasonal prediction of Asian monsoon, proper representation of stratification is essential. This study advocates the need of accurate representation of upper ocean salinity in GODAS for improved stratification. We speculate that improved stratification and mixing in the BoB improve summer monsoon forecas
Preliminary observations and simulation of nocturnal variations of airglow temperature and emission rates at Pune (18.5°N), India
No full textPreliminary observations of the nocturnal variations of the OH(6-2) and O2b(0-1) nighttime airglow in the mesosphere and lower thermosphere are investigated in the context of tidal influence for the tropical latitude station Pune (18.5°N, 73.85°E). This is the only tropical Spectral Airglow Temperature Imager (SATI) station where the tidal variations of mesosphere and lower thermosphere (MLT) temperature have been determined from ground based SATI observations. The SATI observations obtained since October 2012 reveal the influence of the migrating semidiurnal tides during solstice at this tropical station. There is variability in amplitude and phase obtained from SATI observations. In this paper, SATI observations on 10 Dec 2012 and 3 March 2013 are compared with Whole Atmosphere Community Climate Model (WACCM) simulations. The amplitude of semidiurnal tides is ~25 K/30 K on 10 Dec 2012 during solstice for OH/O2 temperature. During equinox SATI data indicates existence of semidiurnal tide also. The airglow observations are compared with simulations from the WACCM. The model underestimates the amplitude of the semi diurnal tide during equinox (1.6 K/2.7 K at 87 km/96 km) and solstice (~3.8 K/4.8 K at 87 km/96 km) for these days. The reason may be related to dampening of tides in the model due to the effect of strong latitudinal shear in zonal wind. The diurnal variation of airglow emission – which the model simulates well – is related to the vertical advection associated with the tides and downward mixing of atomic oxygen
Atmospheric CO2 source and sink patterns over the Indian region
Get PDFIn this paper we examine CO2 emission hot spots and sink regions over India as identified from global model simulations during the period 2000–2009. CO2 emission hot spots overlap with locations of densely clustered thermal power plants, coal mines and other industrial and urban centres; CO2 sink regions coincide with the locations of dense forest. Fossil fuel CO2 emissions are compared with two bottom-up inventories: the Regional Emission inventories in ASia (REAS v1.11; 2000–2009) and the Emission Database for Global Atmospheric Research (EDGAR v4.2) (2000–2009). Estimated fossil fuel emissions over the hot spot region are ∼ 500–950 gC m−2 yr−1 as obtained from the global model simulation, EDGAR v4.2 and REAS v1.11 emission inventory. Simulated total fluxes show increasing trends, from 1.39 ± 1.01 % yr−1 (19.8 ± 1.9 TgC yr−1) to 6.7 ± 0.54 % yr−1 (97 ± 12 TgC yr−1) over the hot spot regions and decreasing trends of −0.95 ± 1.51 % yr−1 (−1 ± 2 TgC yr−1) to −5.7 ± 2.89 % yr−1 (−2.3 ± 2 TgC yr−1) over the sink regions. Model-simulated terrestrial ecosystem fluxes show decreasing trends (increasing CO2 uptake) over the sink regions. Decreasing trends in terrestrial ecosystem fluxes imply that forest cover is increasing, which is consistent with India State of Forest Report (2009). Fossil fuel emissions show statistically significant increasing trends in all the data sets considered in this study. Estimated trend in simulated total fluxes over the Indian region is ∼ 4.72 ± 2.25 % yr−1 (25.6 TgC yr−1) which is slightly higher than global growth rate ∼ 3.1 % yr−1 during 2000–2010