A statistical technique for determination of withdrawal of northeast monsoon over coastal Tamilnadu

The withdrawal dates of northeast monsoon over coastal Tamil Nadu for the 90-year period (1901-90) have been objectively derived. The methodology of determination was generally based on an index based on the spatial distribution of daily rainfall over stations of coastal Tamil Nadu, over a 5-day pentad for the six month period, September- February. The normal withdrawal date thus obtained was 27 December with a standard deviation of 13.6 days and range 23 November-28 January. The duration of northeast monsoon was distributed with mean 67.5 days, standard deviation 14.9 days and range 26-102 days. During 36.7 % of years the withdrawal spilled over to January of next year. The daily normal rainfall and its difference filter have been discussed with reference to the normal date of withdrawal. The average decrease of rainfall at the time of withdrawal has been derived by application of superposed epoch analysis. It has further been shown that during years when the withdrawal took place in January the intensity of northeast monsoon prior to withdrawal was as intense as in years when withdrawal occurred in December. A few cases of northeast monsoon withdrawal have been illustrated with diagrams. As no definite dynamic or thermodynamic features could be uniquely identified which are associated with the withdrawal, this technique is basically statistical, considering the behaviour of the daily normal rainfall as the sole criterion. Unique thermodynamic and dynamic features are not identifiable which are associated with the withdrawal of northeast monsoon over coastal Tamilnadu.

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Rainfall Profile of Cauvery Delta Zone of Tamil Nadu

Current World Environment ◽

10.12944/cwe.11.2.21 ◽

2016 ◽

Vol 11 (2) ◽

pp. 524-530

Author(s):

N. K Sathyamoorthy ◽

R Jagannathan ◽

A. P Ramaraj

Keyword(s):

Tamil Nadu ◽

Southwest Monsoon ◽

Cold Weather ◽

Northeast Monsoon ◽

Water Crisis ◽

Canal Irrigation ◽

Increasing Trend ◽

Hot Weather ◽

Cauvery Delta ◽

Normal Rainfall

Thanjavur and Nagapattinam districts of Cauvery Delta Zone (CDZ) depend on canal irrigation for agriculture and are subjected to the vagaries of monsoon. This creates water crisis and affects agriculture of the region considered as rice bowl of Tamil Nadu. This necessitated the study of rainfall to plan and mitigate water scarcity. Rainfall data from Adhirampattinam, Aduthurai stations of Thanjavur district (Inland) and Nagapattinam station (Coastal area of Nagapattinam district) were utilized for the study. Normal rainfall of CDZ is 956 mm; Nagapattinam receives highest (1350 mm) and aduthurai (994 mm) recorded lowest. November is the wettest month for all locations while driest month differs among locations. Northeast monsoon (NEM) was considered as stable monsoon for CDZ as could be seen from the seasonal mean of 641 mm, 620 mm and 919 mm recorded by Adhirampattinam, Aduthurai and Nagapattinam, respectively. Trend analysis of seasons revealed that Adhirampattinam and Nagapattinam follow a decreasing trend for rainfall and rainydays during NEM and Southwest monsoon (SWM), with an increasing trend for Hot weather period (HWP) and Cold weather period (CWP). An interesting deviation is that Aduthurai recording an increasing trend for NEM while it followed same trend for HWP and SWM.

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Objective determination of northeast monsoon onset dates over coastal Tamil Nadu for the period 1901-90

MAUSAM ◽

10.54302/mausam.v43i3.3455 ◽

2021 ◽

Vol 43 (3) ◽

pp. 273-282

Author(s):

Y. E. A. RAJ

Keyword(s):

Tamil Nadu ◽

Daily Rainfall ◽

Onset Date ◽

Northeast Monsoon ◽

Objective Method ◽

Abrupt Increase ◽

Statistical Parameters ◽

The Mean ◽

Objective Determination

The onset dates of northeast monsoon over coastal Tamil Nadu have been determined by adopting an objective method for the years 1901-90. The various statistical parameters associated with onset dates have been computed and interpreted. Relation between onset dates of easterlies and northeast monsoon over Tamil Nadu has been examined. The normal date obtained has been shown to be by and large consistent with the characteristics of normal daily rainfall of coastal Tamil Nadu. The superposed epoch method has been, used to compute the mean rainfall with reference to onset date and the abrupt increase in rainfall at onset has been clearly brought out The spatial distribution and intensity of rainfall at the time of onset have also been discussed. Daily rainfall has been graphically presented for some years with spectacular onset as well as for some years with subdued onset.

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Characteristics of movement of low level clouds associated with onset / wet spells of northeast monsoon of Indian sub-continent as derived from high resolution INSAT OLR data

MAUSAM ◽

10.54302/mausam.v67i2.1302 ◽

2021 ◽

Vol 67 (2) ◽

pp. 357-376

Author(s):

B. AMUDHA ◽

Y. E. A. RAJ ◽

R. ASOKAN

Keyword(s):

High Resolution ◽

Tamil Nadu ◽

North Indian Ocean ◽

Wave Radiation ◽

Sri Lankan ◽

Northeast Monsoon ◽

Peninsular India ◽

Superposed Epoch Analysis ◽

The North ◽

Epoch Analysis

Characteristics of the northeast monsoon (NEM) have been studied utilising the outgoing long wave radiation (OLR) data derived over the north Indian Ocean and south peninsular India (SPI) from the series of Indian geostationary satellites. The contrasting feature of movement of the equatorial cloud zone from southeast to northwest direction during the onset phase of NEM has been reiterated using 1° × 1° gridded high resolution OLR data for the period 2000-2012. Presence of OLR values less than 180 Wm-2 over a large part of coastal Tamil Nadu on the date of onset and the simultaneous commencement of rainfall with clouding approaching SPI from southeast is clear from the study of superposed epoch analysis of the data. Triad means of OLR also substantiate this inference. During active spells of NEM which succeed prolonged dry spells, replication of the south to north movement of clouding by the OLR contours and the plausible reasons for such a movement have been brought out. The active monsoon situation existing over Sri Lankan region during the withdrawal phase of NEM over SPI is demonstrated with the depiction of the movement of OLR contours less than 230 Wm-2 over the region.

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Breaks in monsoon and related precursors

MAUSAM ◽

10.54302/mausam.v53i3.1647 ◽

2022 ◽

Vol 53 (3) ◽

pp. 309-318

Author(s):

U. S. DE ◽

R. K. MUKHOPADHYAY

Keyword(s):

Daily Rainfall ◽

Equatorial Region ◽

Wave Radiation ◽

Large Area ◽

Time Section ◽

Middle Troposphere ◽

Latitudinal Belt ◽

Anomaly Pattern ◽

Rainfall Departure ◽

Normal Rainfall

A comprehensive analysis of eleven break monsoon situations that occurred during the period 1987 to 1997 have been attempted in the study. The various features like daily rainfall departures, wind anomalies and the satellite derived Outgoing Long wave Radiation (OLR) associated with the commencement/cessation of the break monsoon condition are studied with a view to identifying the precursors associate the break situation. The results reveal that there is progressive decrease of below normal rainfall departures 5 days prior to the actual break day in the latitude belts south of 20° N. During the period of the revival of the monsoon, the time section of the daily rainfall departures shows that the daily rainfall departure first starts becoming above normal in the southern most latitudinal belt 5° N to 10°N from the second day onwards after the cessation of the break. Similarly, the easterly anomalies in the zonal wind are first noticed in the southern latitude even 5 days prior to the starting of the break in the lower and middle troposphere. The maximum easterly anomalies in the lower and the middle troposphere move northwards upto 20° N. The composite latitudinal time section of OLR anomaly show a large area of negative OLR anomaly extending from 20°S to 10°N. The area is defined as the Southern. Hemispheric Convective Zone ( SHCZ). The negative OLR anomaly (10 Wm-2 is noticed around 5° S to 0° N. It increases to 20 Wm-2 on the second day of the break on the same latitudinal belt. The daily OLR anomaly pattern shows that the area of the negative OLR anomaly around the equatorial region increases with the approach of a break epoch. The forecasting aspects of the commencement / cessation of the break have been also discussed.

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Investigation of direct solar proton impact on Arctic stratospheric ozone

10.5194/egusphere-egu21-14507 ◽

2021 ◽

Author(s):

Jia Jia ◽

Antti Kero ◽

Niilo Kalakoski ◽

Monika E. Szeląg ◽

Pekka T. Verronen

Keyword(s):

Climate Model ◽

Model Simulation ◽

Stratospheric Ozone ◽

Individual Case ◽

Solar Proton ◽

Observation Data ◽

Ozone Level ◽

Superposed Epoch Analysis ◽

Average Decrease ◽

The Individual

<p>Recent studies reported up to a 10&#8201;% average decrease of lower stratospheric ozone at &#8764;&#8201;20&#8201;km altitude following solar proton events (SPEs), based on superposed epoch analysis (SEA) of ozonesonde anomalies. Our study uses 49 SPEs that occurred after the launch of Aura MLS (2004&#8211;now) and 177 SPEs that occurred in the WACCM-D (Whole Atmosphere Community Climate Model with D-region ion chemistry) simulation period (1989&#8211;2012) to evaluate Arctic polar atmospheric ozone changes following SPEs. At the mesospheric altitudes a statistically significant ozone depletion is present. At the lower stratosphere (<25 km), SEA of the satellite dataset provides no solid evidence of any average direct SPE impact on ozone. In the individual case studies, we find only one potential case (January 2005) in which the lower-stratospheric ozone level was significantly decreased after the SPE onset (in both model simulation and MLS observation data). However, similar decreases could not be identified in other SPEs of similar or larger magnitude. We find a very good overall consistency between WACCM-D simulations and MLS observations of SPE-driven ozone anomalies both on average and for the individual cases, including case in January 2005.</p>

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A Step towards Integrating CMORPH Precipitation Estimation with Rain Gauge Measurements

Advances in Meteorology ◽

10.1155/2018/2095304 ◽

2018 ◽

Vol 2018 ◽

pp. 1-24

Author(s):

Augusto José Pereira Filho ◽

Felipe Vemado ◽

Guilherme Vemado ◽

Fábio Augusto Gomes Vieira Reis ◽

Lucilia do Carmo Giordano ◽

...

Keyword(s):

Standard Deviation ◽

Amazon Basin ◽

Daily Rainfall ◽

Rain Gauge ◽

Brazilian Coast ◽

Rainfall Estimation ◽

Peruvian Andes ◽

Positive Tendency ◽

Analysis Scheme ◽

Areal Rainfall

Accurate daily rainfall estimation is required in several applications such as in hydrology, hydrometeorology, water resources management, geomorphology, civil protection, and agriculture, among others. CMORPH daily rainfall estimations were integrated with rain gauge measurements in Brazil between 2000 and 2015, in order to reduce daily rainfall estimation errors by means of the statistical objective analysis scheme (SOAS). Early comparisons indicated high discrepancies between daily rain gauge rainfall measurements and respective CMORPH areal rainfall accumulation estimates that tended to be reduced with accumulation time span (e.g., yearly accumulation). Current results show CMORPH systematically underestimates daily rainfall accumulation along the coastal areas. The normalized error variance (NEXERVA) is higher in sparsely gauged areas at Brazilian North and Central-West regions. Monthly areal rainfall averages and standard deviation were obtained for eleven Brazilian watersheds. While an overall negative tendency (3 mm·h−1) was estimated, the Amazon watershed presented a long-term positive tendency. Monthly areal mean precipitation and respective spatial standard deviation closely follow a power-law relationship for data-rich watersheds, i.e., with denser rain gauge networks. Daily SOAS rainfall accumulation was also used to calculate the spatial distribution of frequencies of 3-day rainfall episodes greater than 100 mm. Frequencies greater than 3% were identified downwind of the Peruvian Andes, the Bolivian Amazon Basin, and the La Plata Basin, as well as along the Brazilian coast, where landslides are recurrently triggered by precipitation.

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An Introduction to Fuzzy Testing of Multialternative Hypotheses for Group of Samples with the Single Parameter: Through the Fuzzy Confidence Interval of Region of Acceptance

Journal of Applied Mathematics ◽

10.1155/2015/365304 ◽

2015 ◽

Vol 2015 ◽

pp. 1-8

Author(s):

Manikandan Harikrishnan ◽

Jeyabharathi Sundarrajan ◽

Muthuraj Rengasamy

Keyword(s):

Standard Deviation ◽

Statistical Significance ◽

Group Testing ◽

Fuzzy Group ◽

Classical Statistics ◽

Two Samples ◽

Significant Difference ◽

Alternative Hypotheses ◽

Sole Criterion ◽

First Time

Classical statistics and many data mining methods rely on “statistical significance” as a sole criterion for evaluating alternative hypotheses. It is very useful to find out the significant difference existing between the samples as well as the population or between two samples. But in this paper, the researchers try to apply the concepts of fuzzy group testing of hypothesis problem between multi group of samples of same size or different, through comparing the parameters like mean, standard deviation, and so forth. Hence we can compare multigroups such that they have the significant difference in their mean or standard deviation or other parameters through the fuzzy group testing of multihypotheses. The authors introduced and investigated the concepts very first time through fuzzy analysis that can decide which group(s) or samples can be taken for further investigation and eitherH0is rejected or accepted and hence the next discussion provides the properties of group of samples which may result in the optimized solution for the problem.

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Spatial variation of clouding / rainfall over southeast Indian peninsula and adjoining Bay of Bengal associated with active and dry spells of northeast monsoon as derived from INSAT OLR data

MAUSAM ◽

10.54302/mausam.v67i3.1369 ◽

2021 ◽

Vol 67 (3) ◽

pp. 559-570

Author(s):

B. AMUDHA ◽

Y. E. A. RAJ ◽

R. ASOKAN

Keyword(s):

Spatial Variation ◽

Tamil Nadu ◽

Active Phase ◽

Wave Radiation ◽

Northeast Monsoon ◽

Peninsular India ◽

North East ◽

The North ◽

Northern Latitudes ◽

Dry Spells

South Peninsular India (SPI) benefits largely from the rainfall (RF) realised during the North East Monsoon (NEM) season that prevails from October to December spilling over to January in some of the years. Salient aspects of clouding / RF over SPI associated with 13 NEM seasons from 2000-01 to 2012-13 have been analysed using estimates of Outgoing Long wave Radiation (OLR) at 1° × 1° resolution derived from the radiance observations in the infra-red channel onboard the geostationary operational Indian satellite (INSAT) radiometers. OLR is considered as a proxy indicator for convective activity with the value of 230 Wm-2 as the threshold for RF occurrence. Year-to-year mean OLR patterns of the NEM season along with the latitudinal and longitudinal variabilities were analysed for dry, light and active phases of NEM. Based on rigorous analysis of INSAT OLR data for the above 13 years, it has been shown that during the active phase of NEM, Coastal Tamil Nadu (CTN) receives more RF while over BoB the RF is lower and decreases sharply over interior Tamil Nadu. This is a reiteration of a similar result from an earlier study based on 3 years (1996-98) OLR data from polar orbiting NOAA satellites. The spatial variation in OLR over the latitudes of 10.5, 12.5 and 14.5° N along the longitudes of 75.5-85.5° E has revealed the feature that north of 10.5° N, values of OLR are higher with decrease in RF from south to north. During dry phase of NEM in December and January, higher OLR is observed over northern latitudes of BoB than southern latitudes. It has been comprehended that in the southern latitudes of BoB, where higher sea surface temperatures (SST) are prevalent, more moisture is generated and pumped in to upper levels of the atmosphere leading to lower values of OLR compared to northern latitudes.

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OUTLOOK ON NORTHEAST MONSOON RAINFALL OF TAMIL NADU

MAUSAM ◽

10.54302/mausam.v44i1.3739 ◽

2021 ◽

Vol 44 (1) ◽

pp. 19-22

Author(s):

Y.E.A. RAJ ◽

P. N. SEN ◽

S. M. JAMADAR

Keyword(s):

Multiple Regression ◽

Tamil Nadu ◽

Monsoon Rainfall ◽

Northeast Monsoon ◽

Northeast Monsoon Rainfall ◽

The Mean ◽

In The Beginning

The mean monthly wind vectors at 850, 500 and 150 hPa levels over Thiruvananthapuram (TRV) and Madras (MDS) for August. and September have been subjected to stepwise screening. The objective is to develop a scheme capable of providing an outlook of .northeast monsoon rainfall of Tamil Nu in the beginning of October. A multiple regression scheme of S1K predictors has been identified. The scheme developed from 23•year data performed well when te.ted in an independent five-year period.

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Extreme rainfall and drought events in Tamil Nadu, India

Climate Research ◽

10.3354/cr01600 ◽

2020 ◽

Vol 80 (3) ◽

pp. 175-188

Author(s):

R Rajkumar ◽

CS Shaijumon ◽

B Gopakumar ◽

D Gopalakrishnan

Keyword(s):

Tamil Nadu ◽

Daily Rainfall ◽

India Meteorological Department ◽

Extreme Rainfall ◽

Drought Severity ◽

Extreme Rainfall Events ◽

Rainfall Events ◽

Significance Level ◽

Spatio Temporal ◽

Temporal Dimensions

In the present study, we examined the exposure of the Tamil Nadu region, India, to droughts and extreme rainfall events using the Standardised Precipitation Evapotranspiration Index (SPEI) and a classification scheme based on daily rainfall. We used high-resolution temperature and rainfall observations from the India Meteorological Department for the period 1951-2016. The robustness of the results was tested using the Mann-Kendall trend (M-K) test and the Kolmogorov-Smirnov (K-S) test. During the study period, there were statistically significant increasing trends in drought area (90% significance level), maximum drought intensity (99% significance level) and maximum drought severity (99% significance level) over the Tamil Nadu region. There has also been an increase in the frequency and intensity of heavy rainfall events in recent years. The spatio-temporal dimensions of this study suggest an increasing exposure of this semi-arid, rain shadow region to severe droughts and extreme rainfall events in recent decades. The results provide sufficient grounds to substantiate the necessity of immediate interventions at the policy level.

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