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TODAY: CAOS: PhD Thesis Colloquium: 03 March 2020 (Tuesday): 3:30 pm
Title: "Effects of aerosols and atmospheric boundary layer dynamics on refractive index fluctuations: implications for Free-Space Optical communication"

Candidate: Mr. Anand N

Date: 03 March 2020 (Tuesday)

Time: 3:30 PM

Venue: CAOS Seminar Hall

Tea/Coffee at 3:15 pm



Laser communication through atmospheric channels is an emerging wireless technology,commonly known as Free-Space Optical (FSO) communication. It facilitates unprecedented channel capacity and very large bandwidth favoring huge-volume data transfer across spatially separated locations. Such systems essentially consist of a laser beam pointed towards a distant photodetector and are devoid of bulky copper cables or optical fibers. However, the performance of FSO links depend largely on the atmospheric channel state. There are two main processes leading to signal degradation in FSO links: attenuation due to scattering and/or absorption and intensity fluctuations due to scintillation and/or beam wander (represented using the refractive index structure parameter Cn2). While the attenuation effects can be quantified and compensated, it is very difficult to quantify Cn2 owing to the inherent randomness of atmospheric turbulence. When present within the atmospheric channel, aerosols, the tiny solid/liquid particles suspended in the air, can cause reduction in received signal through absorption and scattering and by additional quasi-random modulations of Cn2; understanding of both being critical to designing of efficient and all-weather links. Due to its large spatio-temporal, and vertical variations and wide range of physical, optical and chemical properties, aerosols can introduce considerable inhomogeneity in the atmosphere.

Investigations from this thesis establish the hitherto unlooked dependence of Cn2 on the aerosol radiative effects. The roles of residence time, concentration and vertical distribution of aerosols are delineated. The influence of aerosols on Cn2 was found to be strong enough to induce a regime shift from weak to moderate turbulence. On the other hand, absorption of solar radiation by elevated aerosol black carbon (BC) layers increases the atmospheric stability and suppresses the refractive index fluctuations thereby favoring better channel properties. An increase in signal absorption is compensated by the large decrease in Cn2 and have strong implications for aerial FSO communication links. The possible use of elevated BC layers as proxies for identifying conducive altitudes for high-performance aerial FSO links is put forward. In order to characterize the seasonality in diurnal variations of Cn2 and aerosols, and their combined effects on FSO communication, concurrent and collocated observations of aerosols and the state of turbulence of atmospheric boundary layer (ABL) have been carried out at the climate research laboratory in the second campus of IISc at Challakere, for over one full year. These observational data are used to characterize the diurnal changes and its seasonality in optical link performances. Strong inverse dependency, controlled by the time of the day, exists between BC and Cn2. Merits of low nocturnal Cn2 are vitiated by the high attenuation caused by increased aerosol concentration resulting from confinement by the capping inversions. Fractional contribution of aerosols to optical attenuation is significant and shows large diurnal variations. Competing effects of Cn2 and aerosols on atmospheric links are estimated for different environmental conditions. Daytime attenuation is largely dominated by Cn2 while the nighttime values are dependent on the aerosol concentration as well. Finally, the effects of aerosols and ABL dynamics on the performance of ground-to-satellite FSO communication links are characterized, in terms of data rate, coherence length and scintillation index of the communication link. Existing Cn2 models do not account for the aerosol effects explicitly/realistically. Results from this thesis put forward the requirement of incorporating the effects of aerosols in Cn2 models and during the estimation of FSO communication link budget.


S. K. Satheesh

Chair, Divecha Centre for Climate Change
Professor, Centre for Atmospheric and Oceanic Sciences
Indian Institute of Science
Bengaluru, India
Tel: 91-80-2293 3070; Fax: 91-80-2360 0865


CAOS Seminar Today : 03 March 2020: 2:30PM: Impact of Climate Change on Coastal Environment and Coastlines of India

Title: " Impact of Climate Change on Coastal Environment and Coastlines of India”
Speaker: Prof. Manasa Ranjan Behara,  Dept. Civil Engg.,  IIT Mumbai
Date: 03 March 2020 (Tuesday)
Time: 2:30 PM
Venue: CAOS Seminar Hall
High Tea after the Seminar at 3:15 PM


Long-term changes in wave climate have potential impacts on the evolution of regional coastlines. This study investigates the impact of variable wave climate on the temporal dynamics of longshore sediment transport (LST), which plays a major role in defining the overall coastal geomorphology of regional coastlines. The swell wave induced sediment transport is an order of magnitude higher than the wind wave induced LST. Both swell and wind wave induced LST show seasonal variation. A link is established between the seasonal variation of swell induced LST and the cyclogenesis periods. In addition, the wind wave induced LST is observed to have a direct link with the latitudinal position of the inter-tropical convergence zone (ITCZ).

Near-surface winds, derived from GCMs and RCMs are used to force a spectral wave model to simulate hindcast waves over Indian Ocean (IO) region. RCMs work at fine resolution and are assumed to simulate regional climate better than GCMs. However, we identified that there is no added value in simulating wave climate using RCMs. We also identified that there is no improvement in wave simulation upon choosing a fine resolution GCM (~ 1.4°) over a coarse GCM (~ 2.5°). It is observed that ensemble GCM forced wave simulations capture seasonality better than other models. Finally, it is recommended to use ensemble GCM wind forcing for better wave simulation in the IO region. The regional wave climate along the Indian coast for two time slices, 2011–2040 and 2041–2070, is reported using an ensemble of near-surface winds generated by four different CMIP5 general circulation models (GCMs), under RCP4.5 scenario. Comparison of the wave climate for the two time slices shows an increase in wave heights and periods along much of the Indian coast, with the maximum wave heights increasing by more than 30% in some locations. An important finding is that at most locations along the east coast, wave periods are expected to increase by almost 20%, whereas along the west coast an increase of around 10% is expected. This will alter the distribution of wave energy at the shoreline through changes in wave refraction and diffraction, with potential implications for the performance and design of coastal structures and swash-aligned beaches. Furthermore, the computations show material changes in the directional distribution of waves. This is particularly important in determining the longshore transport of sediments and can lead to realignment of drift-aligned beaches, manifesting itself as erosion and/or siltation problems.

We assessed the changes in potential longshore transport rates along the Indian coast due to the potential changes in wave parameters under the RCP4.5 climate scenario. The projected wave climate for two time slices, present (2006-2030) and future (2051-2075) were used to investigate the changes in the corresponding sediment transport rates. A holistic empirical model that accounts for the major wave parameters (like wave height, period, and direction), longshore current and the resulting sediment transport, and shoreline evolution, was used in this study. Similar characterisations, carried out for present and future time slices showed that about 35% of the total coastline would remain unaffected due to the changing wave climate in the future time slice; about 20% is expected to “worsen”; and 45% to “improve”.

Dr.  P. N. Vinayachandran

Professor &  J C Bose National Fellow
Centre for Atmospheric and Oceanic Sciences | Indian Institute of Science | Bangalore 560 012 | Tel: +91 80 2293 3065


Ph. D. Thesis Defense: CAOS: TODAY: 11:00 AM, Impact of river runoff into the ocean on climate in a coupled model

Title: " Impact of river runoff into the ocean on climate in a coupled model"

Candidate: Mr. Jahfer Sharif K. K.

Date: 03 March 2020 (Tuesday)
Time: 11:00  AM
Venue: CAOS Seminar Hall
Tea/Coffee at 10:45 AM


 Rivers of the world discharge about 40 x 103 km3 of freshwater into the oceans, yet the impact of runoff on climate is not well known. Using a coupled model, the response of oceans and climate to river discharge is investigated in this thesis. Model experiments were carried out for a period of 200 years by switching off or doubling the river discharge into the ocean. In one such experiment, the runoff into the ocean was intercepted globally. Model studies show that the largest changes in SST were found to be away from the river mouth where the SSS anomalies are high. While the northern Atlantic and Pacific Oceans exhibited warmer SST without the runoff, the equatorial and southern tropical oceans become cooler. The cooling in the equatorial Pacific Ocean resembles the La Niña phase of El Niño Southern Oscillation (ENSO) and consequently the Indian summer monsoon rainfall (ISMR) enhanced. Based on existing theories, we find that the equatorial Pacific affects the ISMR through upper tropospheric meridional temperature via the westward propagating jet termed as the North African–Asian Jet (NAA). The resultant negative vorticity anomalies over the Asian landmass during a La Niña phase leads to overall warming over the region that reinforces the meridional temperature gradient between equatorial Indian Ocean and landmass over Asia, strengthening the ISMR.


The objective of the second part of this study is to investigate the role of Amazon runoff on climate. In this section, we examine the climatic response to fluctuations in the Amazon river runoff into the equatorial Atlantic Ocean. We find that the Amazon river runoff has a major impact on the Atlantic Ocean, Europe, and North America. In the absence of Amazon runoff, the Atlantic meridional overturning circulation (AMOC) strengthens and the Atlantic Ocean turns warmer in the northern hemisphere, and cooler water spreads in the equatorial and South Atlantic Ocean. In the boreal winter, an enhanced AMOC weakens the atmospheric ascending motion and thereby the Hadley cell strength over the equatorial Atlantic Ocean. Consequently, the meridional cells in the mid-latitude and extratropics also weaken. The surface ocean and atmospheric anomalies in the absence of Amazon runoff resemble spatial patterns of anomalies during a negative phase of North Atlantic Oscillation (NAO). The boreal wintertime northern Europe and the eastern United States turn cooler and drier in the absence of Amazon runoff and southern Europe and eastern Canada experience warmer and wetter winters. During boreal summer, there are significant changes in rainfall in the tropical Atlantic sector. When Amazon runoff is absent, the AMOC enhances, and large–scale warming appears in the North Atlantic Ocean (positive AMV). This positive phase of AMV favors a more northerly position of intertropical convergence zone (ITCZ) during boreal summer. Changes in rainfall patterns affect the local freshwater budget in the Atlantic Ocean and the rainfall over northwest Africa.


In order to study the impact of runoff into the Bay of Bengal, coupled model experiments were carried out with and without runoff into the Bay for a period of 200 years. When the runoff into the Bay is intercepted, the surface salinity in the upper ocean increases and the mixed layer becomes deeper. On short–timescale (1–10 years), the response of the climate system to the change in runoff is contrasting in summer and winter. During winter, the western equatorial Indian Ocean turns warmer in the first ten years whereas, during summer, the largest cooling is found in the eastern half. Significant changes in rainfall over India is observed during June and September.


Results from the coupled model experiments show how climatically significant is the freshwater input from the rivers. Modification of runoff reaching the ocean can have a significant impact on climate at a wide range of spatial and temporal scales. The impact of runoff on the climatic oscillations like ENSO, monsoon, NAO, AMO, AMOC, etc., shows that the impacts are not just confined to local oceanic regions where the runoff enters. Further, detailed studies on the changes in the freshwater usage and its impacts need to be done to better understand the climatic roles of the freshwater components of the earth system.




Dr.  P. N. Vinayachandran

Professor &  J C Bose National Fellow
Centre for Atmospheric and Oceanic Sciences | Indian Institute of Science | Bangalore 560 012 | Tel: +91 80 2293 3065

Co-chair, Ocean Predict Science Team

Announcements / CAOS Seminar
« on: July 29, 2019, 12:55:48 PM »


Dear students,

The Tata Trusts has made a generous contribution to support the travel of
several IISc PhD students to international conferences between Mar 2019 -
Feb 2020. 

We invite PhD students to apply for this grant by filling the form at the

Prerequisites for application:
Should be pursuing a PhD programme at IISc
Should have completed comprehensive examination
Should have an accepted publication at an international conference/symposium
and furnish evidence of the same

Required documents:
Proof/confirmation of conference publication acceptance
Recommendation letter from PhD Advisor
Copies of grade sheets

Applications will be evaluated periodically (during Apr 2019 - Feb 2020) by
the committee of Divisional Chairs and grants will be disbursed on a rolling
basis, based on the availability of funds. Each selected student can avail
up to Rs. 2 lakhs.

Kindly note that once you receive the grant, any
publications/studies/banners/posters supported by the grant must include the
statement "Supported by the Tata Trusts" wherever applicable. Due
acknowledgement needs to be given to the Tata Trusts on any
research/publishable material.

As the funds are provided through a private contribution, there is no
restriction on using only Air India for travel. Private airlines may also be
used for the international travel.   

For any queries, please write to

Thank you.

Office of Development and Alumni Affairs
Indian Institute of Science

Quantifying the shifts and intensification in the annual cycles of diurnal temperature extremes for human comfort and crop production

Work is carried out by
Vinnarasi Rajendran and Prof. Dhanya C T  from IIT Delhi



CAOS Seminar

Title: Local onset and demise of the Indian summer monsoon and its relation to intraseasonal oscillations

Speaker: Prof V. Misra, Dept. of Earth, Ocean, and Atmospheric Sciences, Florida State University

Date/Time: Wednesday, 20 March 2019, 4:00 PM

Venue: CAOS Seminar Hall

This talk will introduce a relatively new definition for defining the onset and demise of the
Indian summer monsoon (ISM) at a very granular scale that is in fact data adaptive. The
consistency of this local definition with the seasonal changes of the large-scale circulation will
also be discussed. The talk will then show its relationship with the intraseasonal oscillations of
the ISM both from observations and model simulations. Finally, a real time application of
monitoring the onset isochrones with GPM data will be demonstrated.

All Are Welcome.


Carnegie is an equal opportunity employer.  All qualified applicants will receive consideration for employment without regard to race, religion, color, national origin, sex, sexual orientation, gender identity, age, veteran status, disability or any other protected status in accordance with applicable laws.

Apply Now


Carnegie is an equal opportunity employer.  All qualified applicants will receive consideration for employment without regard to race, religion, color, national origin, sex, sexual orientation, gender identity, age, veteran status, disability or any other protected status in accordance with applicable laws.

Apply Now

Announcements / Three 40th anniversaries
« on: February 27, 2019, 12:31:44 PM »

There is an interesting commentary in Nature Climate Change on the 40th Anniversary of the Charney report, a seminal paper on the detection of climate change and satellite-based climate observations. Nicely written.

"Celebrating the anniversary of three key events in climate change science | Nature Climate Change"


Co-Ordinators for the workshop: Prof K.Srinivasa Raju and Prof A.Vasan.

The poster is attached for your reference.

It is requested to circulate the information to faculty, research scholars, PG students of Department and known institutions.   

With regards

Srinivasa Raju



Dr.  Komaragiri Srinivasa Raju, Ph.D.

Professor, Department of Civil Engineering

Birla Institute of Technology and Science Pilani, Hyderabad Campus

Jawahar Nagar, Kapra Mandal

Medchal District 500 078; Telangana, India

Tel: 91-40-6630 3519 (O)




The Abstract submission period ends on February 28th, 2019

Towards a Sustainable Water Future
24 - 27th September 2019 Bengaluru, India
Sheraton Grand Bangalore Hotel at Brigade Gateway 26/1 Dr. Rajkumar Road, Malleswaram-Rajajinagar Bengaluru 560 055, India

Please find the attached flyer on 'call for abstract' as well as the conference website and contact details.

We request you to share the conference information and the flyer with your network and encourage them to submit abstracts. Please let me know if you think we should make any changes to the website, topic lists or the thematic scope. Looking forward to speaking to you all soon.




TITLE: "Attributing observed changes in surface air temperature and rainfall over India"





Observed trends in temperature and rainfall over India are analyzed from a detection and attribution (D&A) perspective. Increasing temperatures over India since the middle of the 20th Century over various homogeneous zones of India were analyzed in a recent study by Dileep kumar et al., (2018) who concluded that observed increases can be attributed to forcings from greenhouse gases that have been offset by other anthropogenic factors (including anthropogenic aerosols and land use land cover change). However, the linear regression based D&A method cannot disaggregate the role of anthropogenic aerosols alone since the response to different forcings is not always linearly additive.


Did you know Indian and West African monsoons are linked?
A report by an IISc scientist says that El Nino oscillates between both regions and affects the intensity of their rainfall

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