Recent Posts

Pages: [1] 2 3 ... 10
A comprehensive analysis of the role of Indo‐Pakistan arid region (IPAR) in modulating the boreal summer heavy extreme rainfall events over monsoon core zone (MCZ over Indian subcontinent) at subseasonal to daily time scales is presented. The objective is to bring new perspectives on the dynamics of such rainfall extremes. Time‐lagged composite analysis shows the clustering of Monsoon Intra‐Seasonal Oscillation with monsoon rainfall daily extremes. However, our results additionally bring out the distinct role of surface thermal forcing and moist processes over IPAR as another potential and significant precursor, 16–10 days in advance, causing monsoon rainfall daily extremes over MCZ. Further analysis reveals that the warming over IPAR is initially found in the northern part of the domain, 20–15 days before the rainfall events over MCZ and is triggered by subtropical‐midlatitude interactions characterized by the intrusion of a midlatitude (i.e., Eurasian) atmospheric wave train into the Asian domain. Our analysis further reveals strong moist static energy (MSE) build‐up over the IPAR 12 days in advance, which is initially dominated by anomalous warming in the lower atmosphere, but with an incremental contribution of low‐level specific humidity as we moved forward in time towards the rainfall event. Hydrodynamic‐longwave radiative teleconnections are the primary mechanism for the persistence of the surface warming and MSE buildup over IPAR after the initial intrusion of the Eurasian wave train. The persistent warming over IPAR reinforces the land‐sea contrast between the Middle East and western equatorial Indian Ocean to its south, and this subsequently leads to pressure anomalies and monsoon circulation changes through geostrophic wind adjustment, thus enhancing westerlies over Arabian Sea. All these factors lead to the development of a gigantic monsoon trough over central India thus causing the rainfall extremes over MCZ through the genesis of synoptic vortices.

Lin to paper:

Geostatistical interpolation methods are used in diverse disciplines, such as environmental science, ecology, and hydrology. With the increasing availability of areal spatial data, area-to-area and area-to-point interpolations have great application potential. In this study, based on the variogram deconvolution algorithm proposed by Goovaerts (2008), an open-source area-to-area kriging package atakrig is developed in the R environment. In atakrig, point-scale variogram and cross-variogram can be automatically deconvoluted from spatial areal samples. It provides a general framework for area-to-area and area-to-point ordinary kriging and cokriging. Two applications show that the package works well in river runoff prediction and missing data interpolation for remote sensing aerosol optical depth. The package can be deployed on different operating systems and computer hardware platforms.


• Point-scale direct- and cross-variograms can be deconvoluted from irregular areas.
• Spatial scaling conversion between different supports implemented based on Kriging.
• A flexible area kriging package for general application developed.

Link to paper:
Hydrological sciences / Estimating 500-m Resolution Soil Moisture
« Last post by Shubham Goswami on March 24, 2020, 09:38:28 PM »
Title: Estimating 500-m Resolution Soil Moisture Using Sentinel-1 and Optical Data Synergy

The aim of this study is to estimate surface soil moisture at a spatial resolution of 500 m and a temporal resolution of at least 6 days, by combining remote sensing data from Sentinel-1 and optical data from Sentinel-2 and MODIS (Moderate-Resolution Imaging Spectroradiometer). The proposed methodology is based on the change detection technique, applied to a series of measurements over a three-year period (2015 to 2018). The algorithm described here as “Soil Moisture Estimations from the Synergy of Sentinel-1 and optical sensors (SMES)” proposes different options, allowing information from vegetation densities and seasonal conditions to be taken into account. The output from this algorithm is a moisture index ranging between 0 and 1, with 0 corresponding to the driest soils and 1 to the wettest soils. This methodology has been tested at different test sites (South of France, Central Tunisia, Western Benin and Southwestern Niger), characterized by a wide range of different climatic conditions. The resulting surface soil moisture estimations are compared with in situ measurements and already existing satellite-derived soil moisture ASCAT (Advanced SCATterometer) products. They are found to be well correlated, for the African regions in particular (RMSE below 6 vol.%). This outcome indicates that the proposed algorithm can be used with confidence to estimate the surface soil moisture of a wide range of climatically different sites.


India’s soil-water systems provide a vital source of freshwater and sustain the drinking water supply for the world’s second-largest population. However, groundwater within the large geographical area of India continues to be affected by geogenic pollution and industrial spills. Thus, an effort has been made to review the studies performed to investigate distributions and behaviors of major pollutants of Indian soil-water systems. Furthermore, a state-of-the-art literature survey has been performed to understand the progress in wetland hydrology and in the estimation of greenhouse gas (GHG) emissions from India’s soil-water systems. The geochemically induced health issues have been presented here. Five major observations have been noted as follows: (1) the majority of aquifers in India are highly affected by multiple pollutants, i.e., arsenic (As), fluoride (F), nitrate (N), selenium (Se), uranium (U), and hydrocarbons; (2) although there is sufficient literature on laboratory and field investigations of individual pollutants’ behavior in India soil-water systems, these investigations haven’t been performed for multipollutants; (3) scant information is available on reactive solute behaviors in Indian wetland systems; (4) significant work has been done in the past to estimate GHG emissions from Indian wetlands, dams/reservoirs, forests, and crop lands, but very limited information is available on its connectivity with local and regional hydrological processes and water quality; (5) large populations are affected by serious health issues such as dental/skeletal fluorosis, malignancy, and hyperkeratosis in areas highly contaminated with multipollutants. This is the first study to present the current status of multi-pollutants’ distributions and behaviors in Indian soil-water systems and associated health hazards. The manuscript will help policy makers, geochemists, and environmental scientists to frame management and remediation plans for polluted sites in India.
Post your question/information / GRACE Preprocessing Steps?
« Last post by Ahmad_Shah on March 10, 2020, 01:41:37 PM »
Dear All.

Can you please help me to find out the steps needed for preprocessing of GRACE satelite data?

Announcements / TODAY: CAOS: PhD Thesis Colloquium: 03 March 2020 (Tuesday): 3:30 pm
« Last post by Sonali on March 03, 2020, 10:45:13 AM »

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
Hydrological sciences / Climate Extremes and Compound Hazards in a Warming World
« Last post by Pankaj Dey on February 25, 2020, 11:26:49 PM »
Climate extremes threaten human health, economic stability, and the well-being of natural and built environments (e.g., 2003 European heat wave). As the world continues to warm, climate hazards are expected to increase in frequency and intensity. The impacts of extreme events will also be more severe due to the increased exposure (growing population and development) and vulnerability (aging infrastructure) of human settlements. Climate models attribute part of the projected increases in the intensity and frequency of natural disasters to anthropogenic emissions and changes in land use and land cover. Here, we review the impacts, historical and projected changes, and theoretical research gaps of key extreme events (heat waves, droughts, wildfires, precipitation, and flooding). We also highlight the need to improve our understanding of the dependence between individual and interrelated climate extremes because anthropogenic-induced warming increases the risk of not only individual climate extremes but also compound (co-occurring) and cascading hazards.

Climate hazards are expected to increase in frequency and intensity in a warming world.
Anthropogenic-induced warming increases the risk of compound and cascading hazards.
We need to improve our understanding of causes and drivers of compound and cascading hazards.
Hydrological sciences / Afternoon rain more likely over drier soils
« Last post by Pankaj Dey on February 23, 2020, 06:49:04 PM »
Land surface properties, such as vegetation cover and soil moisture, influence the partitioning of radiative energy between latent and sensible heat fluxes in daytime hours. During dry periods, soil-water deficit can limit evapotranspiration, leading to warmer and drier conditions in the lower atmosphere1,2. Soil moisture can influence the development of convective storms through such modifications of low-level atmospheric temperature and humidity1,3, which in turn feeds back on soil moisture. Yet there is considerable uncertainty in how soil moisture affects convective storms across the world, owing to a lack of observational evidence and uncertainty in large-scale models4. Here we present a global-scale observational analysis of the coupling between soil moisture and precipitation. We show that across all six continents studied, afternoon rain falls preferentially over soils that are relatively dry compared to the surrounding area. The signal emerges most clearly in the observations over semi-arid regions, where surface fluxes are sensitive to soil moisture, and convective events are frequent. Mechanistically, our results are consistent with enhanced afternoon moist convection driven by increased sensible heat flux over drier soils, and/or mesoscale variability in soil moisture. We find no evidence in our analysis of a positive feedback—that is, a preference for rain over wetter soils—at the spatial scale (50–100 kilometres) studied. In contrast, we find that a positive feedback of soil moisture on simulated precipitation does dominate in six state-of-the-art global weather and climate models—a difference that may contribute to excessive simulated droughts in large-scale models.
Pages: [1] 2 3 ... 10