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Role of Arabian Sea in the evolution of Indian Ocean Dipole
No full textAn Indian Ocean Dipole (IOD) event often evolves without any forcing from the Pacific. This study demonstrates that Arabian Sea spring warming and associated summer barrier layer (BL) play an important role in the evolution of such IODs. We propose an alternate mechanism for IOD initiation. Anomalous Walker circulation over the Indian Ocean during IOD years forced by Arabian Sea warming in spring and summer plays a crucial role in initiating the easterly wind anomalies in the eastern equatorial Indian Ocean. The western warming and the associated convection induce easterly wind anomalies much before the significant eastern cooling during IOD years, which strongly supports the role of western warming in the IOD evolution. IOD years are characterized by anomalous thickening of summer BL over the Arabian Sea. The anomalous BL formation during IOD years is attributed to the anomalous negative Ekman pumping velocity in the Arabian Sea. This negative Ekman pumping velocity forced downwelling deepens isothermal layer depth and thickens the BL. In addition to this, strong precipitation during IOD years strengthened the stratification and supported the BL formation. These favourable conditions for BL formation are absent during El Niño years. Anomalous BL is mainly responsible for the deepening of thermocline and subsurface warming in the Arabian Sea during IOD years
New method to compute the principal components from self-organizing maps: an application to monsoon intraseasonal oscillations
No full textThe study develops a self-organizing map (SOM)-based local principal component analysis (PCA) to obtain the linearly decorrelated principal components (PCs) of monsoon intraseasonal oscillations (MISOs). Although the SOM-derived feature maps are not orthogonal like empirical orthogonal function (EOFs), we show that in the case of MISOs simple mathematical substitution can make the SOM-derived PCs linearly decorrelated to each other. Thus, the SOM-based local PCA is seen also to be statistically equivalent to extended EOF analysis when applied to MISO analysis. The life cycle and phase evolution of MISO through SOM-based PCA is robust and conforms to the results based on extended EOFs besides having potential to give new information. The remarkable similarity of results with the symmetric SOM configurations shows the effectiveness of these methods for use as empirical reduction models for climate patterns. The asymmetric SOM lattice configurations derive similar phase evolution as compared to a symmetric lattice, but asymmetric temporal evolutions in the PC-defined phase space. The results once again endorse the mathematical basis of PCA through SOM for geophysical applications
Measurement of particulate pollution in Jabalpur city during Diwali festival
Get PDFThe ambient air quality monitoring network involves measurement of number of air pollutant. A variety of method exist to measure particular matter in air
IITM Earth System Model: Transformation of a Seasonal Prediction Model to a Long Term Climate Model
No full textWith the goal of building an Earth System Model (ESM) appropriate for detection, attribution and projection of changes in the South Asian monsoon, a state-of-the-art seasonal prediction model, namely the Climate Forecast System version 2 (CFSv2) has been adapted to a climate model suitable for extended climate simulations at the Indian Institute of Tropical Meteorology (IITM), Pune, India. While the CFSv2 model has been skillful in predicting the Indian summer monsoon (ISM) on seasonal time scales, a century-long simulation with it shows biases in the ocean mixed-layer, resulting in a 1.5ºC cold bias in the global mean surface air temperature, a cold bias in the sea surface temperature (SST) and a cooler-than-observed troposphere. These biases limit the utility of CFSv2 to study climate change issues. To address biases, and to develop an Indian Earth System Model (IITM-ESMv1), the ocean component in CFSv2 was replaced at IITM with an improved version, having better physics and an interactive ocean biogeochemistry. A 100-year simulation with the new coupled model (with biogeochemistry switched off) shows substantial improvements, particularly in global mean surface temperature, tropical SST and mixed layer depth. The model demonstrates fidelity in capturing the dominant modes of climate variability such as the ENSO and Pacific Decadal Oscillation. The ENSO-ISM teleconnections and the seasonal lead-lags are also well simulated. The model, a successful result of the Indo-US collaboration, will contribute to the IPCC-AR6 simulations, a first from India
Extended range prediction of active-break spells of Indian summer monsoon rainfall using an ensemble prediction system in NCEP Climate Forecast System
No full textThis study analyses skill of an extended range prediction system to forecast Indian Summer Monsoon Rainfall (ISMR) 3-4 pentads in advance. A series of 45-d forecast integrations starting from 1 May to 29 September at 5-d interval for 7 years from 2001 to 2007 are performed with an ensemble prediction system (EPS) in NCEP Climate Forecast System Version 1 (CFSV1) model. The sensitivity experiments with different amount of perturbation suggest that full tendency perturbation experiment on all basic variables including humidity at all vertical level shows higher dispersion among forecast than other experiments. Spread-error relationship shows that the present EPS system is under-dispersive. The lower bound of predictability is about 10-12 d and upper bound of predictability is found to be 20-25 d for zonal wind at 850 and 200 hPa. The signal-to-noise ratio (SNR) of precipitation (500 hPa geopotential height) reveals that the predictability limit is about 15(18) d over Indian monsoon region. The monsoon zone area averaged precipitation forecasts averaged over 5-d period (pentads) up to 4 pentad lead time are also evaluated and compared with observation. The anomaly correlation coefficients (ACC) reaches zero after pentad 3 (pentad 5) lead for precipitation (dynamical variables). A probabilistic approach is developed from the EPS for extended range forecast applications. The relative operating characteristic (ROC) curves for three categories of precipitation shows that the prediction skill for active and break is slightly higher compared to that of normal category and skillful probabilistic forecasts can be generated for precipitation even beyond pentad 4 lead
Oil pollution in Chilika lagoon: An anthropogenic threat to biodiversity
Get PDFChilika lagoon is situated on the east coast of India and is
spread over three districts of Odisha, namely Puri, Khordha and Ganjam. The water spread area varies between 1165 and 906sq.km during monsoon and summer respectively. It is a hot
spot for biodiversity, and the largest wintering ground for
migratory avian guests on the Indian sub-continent
Tropical Indian Ocean subsurface temperature variability and the forcing mechanisms
No full textThe first two leading modes of interannual variability of sea surface temperature in the Tropical Indian Ocean (TIO) are governed by El Niño Southern Oscillation and Indian Ocean Dipole (IOD) respectively. TIO subsurface however does not co-vary with the surface. The patterns of the first mode of TIO subsurface temperature variability and their vertical structure are found to closely resemble the patterns of IOD and El Niño co-occurrence years
Combined interplay of the Atlantic multidecadal oscillation and the interdecadal Pacific oscillation on rainfall and its extremes over Indian subcontinent
No full textThis study provides a pertinent ground for acquiring deeper insight about the low-frequency variability of precipitation and its extremes over India and its homogeneous monsoon regions under the combined interplay of both the Atlantic multidecadal oscillation (AMO) and the interdecadal Pacific oscillation (IPO). The percent of variance in the total/heavy rainfall on decadal-to-multidecadal timescales that can be attributed to these oceanic indices is 88.3/76.7 for west central and 84.4/72.6 for northeast regions, which implies that the recent changes in rainfall and it extremes over respective regions is mainly caused by internal natural variability. The opposite phases of AMO and IPO together modulates the total/moderate rainfall over west central and northeast regions in an asymmetric manner; whereas their warm phase stimulates the heavy rainfall over west central region, while their opposite phases together influences the precipitation extremes over northeast region. Based on the projected conditions of these oceanic indices the outlook for west central/northeast regions is fairly good/bad and these regions will experience above-/below-normal precipitation in the upcoming decade or two. The rainfall over northwest region is mainly influenced by the IPO and this region will also likely to receive above-normal precipitation in the upcoming decade or so due to the present cold phase of IPO. Wind circulation pattern divulges that during the warm phase of AMO the southwesterlies over Indian region are strengthened by the equatorial Atlantic winds coming through the equatorial Africa, while in the cold phase of IPO it gets strengthen by the easterlies from the equatorial Pacific
Global warming and the weakening of the Asian summer monsoon circulation: assessments from the CMIP5 models
No full textThe evolution of the Asian summer monsoon (ASM) in a global warming environment is a serious scientific and socio-economic concern since many recent studies have demonstrated the weakening nature of large-scale tropical circulation under anthropogenic forcing. But, how such processes affect the ASM circulation and rainfall is still a matter of debate. This study examines the climate model projections from a selected set of Coupled Model Inter-comparison Project 5 (CMIP5) models to provide a unified perspective on the future ASM response. The results indicate a robust reduction in the large-scale meridional gradient of temperature (MGT) at upper levels (200 hPa) over the ASM region, associated with enhanced ascendance and deep tropospheric heating over the equatorial Pacific in the future climate. The differential heating in the upper troposphere, with concomitant increase (decrease) in atmospheric stability (MGT), weakens the ASM circulation, promotes a northward shift of the monsoon circulation and a widening of the local Hadley cell in the eastern Indian sector. An examination of the water vapour budget indicates the competing effects of the thermodynamic (moisture convergence) and dynamics processes (monsoon circulation) on future ASM rainfall changes. The former component wins out over the later one and leads to the intensification of Indian monsoon rainfall in the CMIP5 projections. However, the diagnostics further show a considerable offset due to the dynamic component
Late Quaternary climate variability and vegetation response in Ziro Lake Basin, Eastern Himalaya: A multiproxy approach
No full textPollen, phytolith and stable carbon isotopic records provide new insights into the palaeoenvironmental and palaeoclimatic changes in Ziro Lake Basin, sub-Himalayan Arunachal Pradesh, India since pre-LGM time. Phytoliths record a minor change in grass/woodland cover and appear to be more sensitive than pollen grains to climate fluctuations. Both pollen and non-pollen palynomorph data suggest prevalence of a dense C3 species-dominated moist semi-evergreen forest in the area until the LGM which shows conformity with δ13C data. The phytolith assemblage indicates an alteration in forest cover with expansion of C4 grasses during the LGM. The study further indicates a climatic amelioration with intensification of south-west monsoon during 10.2-3.8ka and an expansion of forest cover. After 3.8ka there was a rising trend of dryness, shrinkage in forest cover, and a slight increase in C4 species while C3 plants dominated. Ecosystem variability also points towards a hydrological transformation in the area since pre-LGM time. Application of coexistence approach on pollen data reveals that prior to the LGM the mean annual temperature and mean annual precipitation were approximately 19.3±0.001°C and 1925±15mm respectively. Between 10.2 and 3.8ka MAT was about 19.4±0.5°C, while MAP was 1901±41.3mm. Between 3.8 and 1.2ka and onwards a slight increase in MAT (~0.3C°) was observed with further decrease in MAP to 1861±33.4mm. During pre and post LGM times, MAT was more or less similar in the Ziro Lake Basin which increased gradually after 3.8ka and was ~1.2C° higher than today. Prior to the LGM, MAP was higher than the present day by 94mm, between 10.2 and 3.8ka by 70mm and since 3.8ka onwards by ~30mm showing a tendency of gradual decline suggesting a consequent increase in dryness