scholarly journals Preferred intra-seasonal circulation patterns of the Indian summer monsoon and active-break cycles

2021 ◽  
Author(s):  
David M. Straus
Keyword(s):  
Cluster Analysis ◽  
Bay Of Bengal ◽  
Synthetic Data ◽  
Central India ◽  
Precipitable Water ◽  
Boreal Summer ◽  
Data Sets ◽  
Seasonal Circulation ◽  
Strong Convection ◽  
Northern Bay Of Bengal

AbstractIntra-Seasonal circulation regimes are identified from a cluster analysis of 5-day mean anomaly fields of 850 hPa horizontal winds from the ERA-Interim reanalysis for the boreal summer season (June–Sept. for 1979–2018) over the region (50°–100° E; 5° S–35° N). The k-means method was applied to the leading 6 principal components yielding k clusters. The degree of clustering is significant compared to synthetic data sets for any value of $$k > 3$$ k > 3 . The circulation is most likely to stay in the same cluster from one pentad to the next; significant transitions (with 95% confidence level) form a cycle. The similarity between the cycle depicted from 4 or 5 clusters and the active-break cycle, as well as the 45-day oscillation, is established by composites of 850 hPa winds, 200 hPa divergence, 500 hPa vorticity and vertical pressure velocity, precipitable water, diabatic heating and rainfall over India: Strong convection over the subtropical Indian Ocean moves to the central Bay of Bengal and central India, subsequently to the northern Bay of Bengal and west Bengal, and then further north into the Himalayas. We also find preferred transitions in which the convection moves equatorward from central India. The number of complete cycles found in 40 summers is 7 in the 4-cluster analysis. The number of times the system undergoes four (three) consecutive legs of the cycle is 16 (31). For 5 clusters only 3 complete cycles are found. sequences of five, four and three consecutive legs occur 10, 11 and 28 times, respectively.

scholarly journals Preferred Intra-seasonal Circulation Patterns of the Indian Summer Monsoon and Active-Break Cycles

2021 ◽  
Author(s):  
David Martin Straus
Keyword(s):  
Cluster Analysis ◽  
Indian Ocean ◽  
Bay Of Bengal ◽  
Bootstrap Method ◽  
Principal Component ◽  
Central India ◽  
Boreal Summer ◽  
Transition Matrices ◽  
Seasonal Circulation ◽  
Strong Convection

Abstract Intra-Seasonal circulation regimes are identified from a cluster analysis of 5-day mean (pentad) anomaly fields of 850 hPa horizontal winds (u,v)from the ERA-Interim reanalysis for the boreal summer season (120 days starting 01June for the years 1979 - 2018) over the broad Indian region (50 o -100 o E; 5 o S - 35 o N). The anomalies are formed with respect to a parabolic (in time) seasonal cycle computed separately for each year, thus filtering out periods of greater than 240 days. The k-means method was applied in the phase space of the leading 6 (12) principal component modes, which explain 65% (78%) of the space-time variance, yielding k clusters. The degree of clustering is significant when compared to synthetic data sets for any value of k > 3. The transition matrices for k=4 and k=5 establish that the system is most likely to stay in the same cluster from one pentad to the next, but that the significant transitions (with 95% confidence level using a modified bootstrap method) form a cycle. The similarity between the cycle as depicted from 4 or 5 clusters is established by composites of 850 hPa (u,v,), 200 hPa divergence, 500 hPa vorticity and vertical pressure velocity, and daily rainfall over India: Strong convection (with large positive divergence and vorticity) over the subtropical Indian Ocean, moves to the central Bay of Bengal and over central India, then subsequently to the northern Bay of Bengal and west Bengal, and then further north into the Himalayas. The Indian rainfall composites show a similar cycle. The phases in which strong convection is seen over central and northern India are seen for about 60% of the time for both k=4 and k=5 analyses. However the 4 cluster analysis also shows a preferred transition in which the convection moves equatorward from central India. The number of complete cycles (including a return to the starting cluster) found in the 40 years of data is 7 in the 4-cluster analysis, while the number of times the system undergoes four (three) consecutive legs of the cycle is 16 (31). Fewer instances of complete cycles are found for 5 clusters (only 3), but sequences of five, four and three consecutive legs occur 10, 11 and 28 times respectively. Composites of the tropics-wide vertically integrated diabatic heating (estimated from ERA5 reanalyses) reproduce the characteristics of the boreal summer intra-seasonal oscillation, with northwest-to-southeast oriented bands of heating moving northward from the tropical Indian Ocean into the subtropics. This depiction of the active-break cycle is particularly useful for diagnosing the cycle in short-range forecasts: as long as pentad anomalies can be formed, they can be assigned to one of the observed clusters described in this paper without the need for further time-filtering.

scholarly journals Observed variability in the current field during summer monsoon experiments -Part I : Northern Bay of Bengal

MAUSAM ◽  
2021 ◽  
Vol 42 (1) ◽  
pp. 17-24
Author(s):  
R. R, RAO ◽  
K. V. SANIL K UMAR ◽  
BASIL MA THBW
Keyword(s):  
Time Series ◽  
Flow Regime ◽  
Bay Of Bengal ◽  
Field Experiments ◽  
Time Series Data ◽  
Series Data ◽  
Data Sets ◽  
Current Field ◽  
Mooring Lines ◽  
Northern Bay Of Bengal

The observed short term. variability in .the current field of the upper layers of the northern Bay of Bengal IS examined utilizing the available time series data sets of current meter records obtained from mooring lines deployed from USSR stationary ship polygons during MONSOON-77 and MONEX-79 field experiments. Supplementary time series data sets on the vertical profiles of temperature and salinity in addition to surface winds were also made use of to describe the observed variability and structure of the horizontal velocity in the upper 200 m water column. Although the thermal regime appeared to be homogeneous within both the observational arrays considerable differences were noticed in the salinity and current regimes. The strong vertical stratification which is variable in the northern Bay of Bengal appeared to have Influenced the observed upper oceanic flow regime. Evidence for Ekman type of balance was rather weak suggesting the importance of baroclinic and river driven circulation modes. A clockwise eddy type of circulation was evident only during MONEX-79 but not during MONSOON- 77. The vector time series of current meter records were subjected to rotary spectral analysis to identity the periodicities of energetic oscillations and to infer the nature of circulation. Three to five-day oscillations in the flow regime were noticed during MONEX- 79.

scholarly journals Estimation of sedimentary proxy records together with associated uncertainty

2014 ◽  
Vol 21 (6) ◽  
pp. 1093-1111 ◽  
Author(s):  
B. Goswami ◽  
J. Heitzig ◽  
K. Rehfeld ◽  
N. Marwan ◽  
A. Anoop ◽  
...  
Keyword(s):  
Probability Distributions ◽  
Synthetic Data ◽  
Central India ◽  
Radiometric Dating ◽  
Surface Erosion ◽  
Data Sets ◽  
Radiometric Calibration ◽  
Proxy Record ◽  
Proxy Records ◽  
Lonar Lake

Abstract. Sedimentary proxy records constitute a significant portion of the recorded evidence that allows us to investigate paleoclimatic conditions and variability. However, uncertainties in the dating of proxy archives limit our ability to fix the timing of past events and interpret proxy record intercomparisons. While there are various age-modeling approaches to improve the estimation of the age–depth relations of archives, relatively little focus has been placed on the propagation of the age (and radiocarbon calibration) uncertainties into the final proxy record. We present a generic Bayesian framework to estimate proxy records along with their associated uncertainty, starting with the radiometric age–depth and proxy–depth measurements, and a radiometric calibration curve if required. We provide analytical expressions for the posterior proxy probability distributions at any given calendar age, from which the expected proxy values and their uncertainty can be estimated. We illustrate our method using two synthetic data sets and then use it to construct the proxy records for groundwater inflow and surface erosion from Lonar lake in central India. Our analysis reveals interrelations between the uncertainty of the proxy record over time and the variance of proxies along the depth of the archive. For the Lonar lake proxies, we show that, rather than the age uncertainties, it is the proxy variance combined with calibration uncertainty that accounts for most of the final uncertainty. We represent the proxy records as probability distributions on a precise, error-free timescale that makes further time series analyses and intercomparisons of proxies relatively simple and clear. Our approach provides a coherent understanding of age uncertainties within sedimentary proxy records that involve radiometric dating. It can be potentially used within existing age modeling structures to bring forth a reliable and consistent framework for proxy record estimation.

Cluster analysis for large data sets: applications to individual aerosol particles from the mid-pacific

1992 ◽  
Vol 50 (2) ◽  
pp. 1488-1489
Author(s):  
Thomas W. Shattuck ◽  
James R. Anderson ◽  
Neil W. Tindale ◽  
Peter R. Buseck
Keyword(s):  
Cluster Analysis ◽  
Chemical Reactivity ◽  
Large Data ◽  
Large Data Sets ◽  
Particle Analysis ◽  
Data Sets ◽  
Halogen Chemistry ◽  
Complete Study ◽  
Components Analysis ◽  
Automated Scanning

Individual particle analysis involves the study of tens of thousands of particles using automated scanning electron microscopy and elemental analysis by energy-dispersive, x-ray emission spectroscopy (EDS). EDS produces large data sets that must be analyzed using multi-variate statistical techniques. A complete study uses cluster analysis, discriminant analysis, and factor or principal components analysis (PCA). The three techniques are used in the study of particles sampled during the FeLine cruise to the mid-Pacific ocean in the summer of 1990. The mid-Pacific aerosol provides information on long range particle transport, iron deposition, sea salt ageing, and halogen chemistry.Aerosol particle data sets suffer from a number of difficulties for pattern recognition using cluster analysis. There is a great disparity in the number of observations per cluster and the range of the variables in each cluster. The variables are not normally distributed, they are subject to considerable experimental error, and many values are zero, because of finite detection limits. Many of the clusters show considerable overlap, because of natural variability, agglomeration, and chemical reactivity.

scholarly journals Bay of Bengal‐East Asia‐Pacific Teleconnection in Boreal Summer

2019 ◽  
Vol 124 (8) ◽  
pp. 4395-4412 ◽  
Author(s):  
Ruowen Yang ◽  
Shu Gui ◽  
Jie Cao
Keyword(s):  
East Asia ◽  
Bay Of Bengal ◽  
Asia Pacific ◽  
Boreal Summer

scholarly journals Low CO2 evasion rate from the mangrove-surrounding waters of the Sundarbans

2021 ◽  
Author(s):  
Anirban Akhand ◽  
Abhra Chanda ◽  
Kenta Watanabe ◽  
Sourav Das ◽  
Tatsuki Tokoro ◽  
...  
Keyword(s):  
Bay Of Bengal ◽  
Dissolved Inorganic Carbon ◽  
Monsoon Season ◽  
Buffering Capacity ◽  
Marine Water ◽  
High Temporal Resolution ◽  
Post Monsoon Season ◽  
Biogeochemical Parameters ◽  
Northern Bay Of Bengal ◽  
The Sundarbans

AbstractGlobally, water bodies adjacent to mangroves are considered significant sources of atmospheric CO2. We directly measured the partial pressure of CO2 in water [pCO2(water)] and related biogeochemical parameters with high temporal resolution, covering both diel and tidal cycles, in the mangrove-surrounding waters around the northern Bay of Bengal during the post-monsoon season. Mean pCO2(water) was marginally oversaturated in two creeks (470 ± 162 µatm, mean ± SD) and undersaturated in the adjoining estuarine stations (387 ± 58 µatm) compared to atmospheric pCO2, and was considerably lower than the global average. We further estimated the pCO2(water) and buffering capacity of all possible sources of the mangrove-surrounding waters and concluded that their character as a CO2 sink or weak source is due to the predominance of marine water from the Bay of Bengal with low pCO2 and high buffering capacity. Marine water with high buffering capacity suppresses the effect of pCO2 increase within the mangrove system and lowers the CO2 evasion even in creek stations. The δ13C of dissolved inorganic carbon (DIC) in the mangrove-surrounding waters indicated that the DIC sources were a mixture of mangrove plants, pore-water, and groundwater, in addition to marine water. Finally, we showed that the CO2 evasion rate from the estuaries of the Sundarbans is much lower than the recently estimated world average. Our results demonstrate that mangrove areas having such low emissions should be considered when up-scaling the global mangrove carbon budget from regional observations.

scholarly journals Methods for estimating uncertainty in factor analytic solutions

2014 ◽  
Vol 7 (3) ◽  
pp. 781-797 ◽  
Author(s):  
P. Paatero ◽  
S. Eberly ◽  
S. G. Brown ◽  
G. A. Norris
Keyword(s):  
Environmental Protection Agency ◽  
Synthetic Data ◽  
Analytic Solutions ◽  
Data Sets ◽  
Random Errors ◽  
Data Set ◽  
Factor Analytic ◽  
Uncertainty Estimates ◽  
Multilinear Engine ◽  
Analytic Models

Abstract. The EPA PMF (Environmental Protection Agency positive matrix factorization) version 5.0 and the underlying multilinear engine-executable ME-2 contain three methods for estimating uncertainty in factor analytic models: classical bootstrap (BS), displacement of factor elements (DISP), and bootstrap enhanced by displacement of factor elements (BS-DISP). The goal of these methods is to capture the uncertainty of PMF analyses due to random errors and rotational ambiguity. It is shown that the three methods complement each other: depending on characteristics of the data set, one method may provide better results than the other two. Results are presented using synthetic data sets, including interpretation of diagnostics, and recommendations are given for parameters to report when documenting uncertainty estimates from EPA PMF or ME-2 applications.

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