Theoretical Foundation of Cyclostationary EOF Analysis for Geophysical and Climatic Variables: Concepts and Examples

Natural variability is an essential component of observations of all geophysical and climate variables. In principal component analysis (PCA), also called empirical orthogonal function (EOF) analysis, a set of orthogonal eigenfunctions is found from a spatial covariance function. These empirical basis functions often lend useful insights into physical processes in the data and serve as a useful tool for developing statistical methods. The underlying assumption in PCA is the stationarity of the data analyzed; that is, the covariance function does not depend on the origin of time. The stationarity assumption is often not justifiable for geophysical and climate variables even after removing such cyclic components as the diurnal cycle or the annual cycle. As a result, physical and statistical inferences based on EOFs can be misleading. Some geophysical and climatic variables exhibit periodically time-dependent covariance statistics. Such a dataset is said to be periodically correlated or cyclostationary. A proper recognition of the time-dependent response characteristics is vital in accurately extracting physically meaningful modes and their space-time evolutions from data. This also has important implications in finding physically consistent evolutions and teleconnection patterns and in spectral analysis of variability-important goals in many climate and geophysical studies. In this study, the conceptual foundation of cyclostationary EOF (CSEOF) analysis is examined as an alternative to regular EOF analysis or other eigenanalysis techniques based on the stationarity assumption. Comparative examples and illustrations are given to elucidate the conceptual difference between the CSEOF technique and other techniques and the entailing ramification in physical and statistical inferences based on computational eigenfunctions. © The authors 2015

Mechanism of Seasonal Arctic Sea Ice Evolution and Arctic Amplification

Sea ice loss is proposed as a primary reason for the Arctic amplification, although the physical mechanism of the Arctic amplification and its connection with sea ice melting is still in debate. In the present study, monthly ERA-Interim reanalysis data are analyzed via cyclostationary empirical orthogonal function analysis to understand the seasonal mechanism of sea ice loss in the Arctic Ocean and the Arctic amplification. While sea ice loss is widespread over much of the perimeter of the Arctic Ocean in summer, sea ice remains thin in winter only in the Barents-Kara seas. Excessive turbulent heat flux through the sea surface exposed to air due to sea ice reduction warms the atmospheric column. Warmer air increases the downward longwave radiation and subsequently surface air temperature, which facilitates sea surface remains to be free of ice. This positive feedback mechanism is not clearly observed in the Laptev, East Siberian, Chukchi, and Beaufort seas, since sea ice refreezes in late fall (November) before excessive turbulent heat flux is available for warming the atmospheric column in winter. A detailed seasonal heat budget is presented in order to understand specific differences between the Barents-Kara seas and Laptev, East Siberian, Chukchi, and Beaufort seas

A new approach to the space–time analysis of big data: application to subway traffic data in Seoul

A prevalent type of big data is in the form of space–time measurements. Cyclostationary empirical orthogonal function (CSEOF) analysis is introduced as an efficient and valuable technique to interpret space–time structure of variability in a big dataset. CSEOF analysis is demonstrated to be a powerful tool in understanding the space–time structure of variability, when data exhibits periodic statistics in time. As an example, CSEOF analysis is applied to the hourly passenger traffic on Subway Line #2 of Seoul, South Korea during the period of 2010–2017. The first mode represents the weekly cycle of subway passengers and captures the majority (~ 97%) of the total variability. The corresponding loading vector exhibits a typical weekly pattern of subway passengers as a function of time and the locations of subway stations. The associated principal component time series shows that there are two occasions of significant reduction in the amplitude of the weekly activity in each year; these reductions are associated with two major holidays—lunar New Year and Fall Festival (called Chuseok in Korea). The second and third modes represent daily contrasts in a week and are associated with taking extra days off before or after holidays. The fourth mode exhibits an interesting upward trend, which represents a general decrease in the number of subway passengers during weekdays except for Wednesday and an increase over the weekends.This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government(MSIP) (No. 2016R1A2B4008237)

A Case of Inadvertent Anterior Chamber and Corneal Stromal Injection with Antibiotics during Cataract Operation

Purpose: To report a case of inadvertent anterior chamber and cornea stromal injection with high dose antibiotics and steroids during cataract operation. Methods: During cataract operation on a 78 year-old female patient, high dose gentamicin (20 mg/0.5 ml) and dexamethasone (2 mg/0.5 ml) were inadvertently injected into the anterior chamber and cornea stroma when making cornea edema for sealing of the incision sites. Anterior chamber irrigation with balanced salt solution (BSS) was immediately administered. On postoperative day one, extensive cornea edema was noted, and best-corrected visual acuity was 0.2. Descemet's membrane folds were observed around the corneal incision sites. Topical 5% NaCl and 1% prednisolone were started. Results: Four weeks postoperatively, corneal edema began to reduce significantly. At four months postoperatively, corneal edema fully resolved, and best-corrected visual acuity was 0.8. However, some Descemet's membrane folds still remained, and a decrease in the number of endothelial cells was noted by specular microscope. Conclusions: In this case involving anterior chamber and cornea stromal injection with high dose antibiotics and steroids, immediate anterior chamber irrigation with balanced salt solution seemed an appropriate management, and the patient's long-term visual acuity appears good. To prevent such mistakes, precise labeling of all solutions and use of different syringe needles should be considered.ope

Availability of the Pediatric Emergency Care Applied Research Network (PECARN) rule for computed tomography scanning decision in children younger than 2 years with minor head injury

Purpose Traumatic brain injury is the most common cause of pediatric injury. Although computed tomography (CT) scan is an effective modality for screening fatal craniocerebral trauma, there is growing concern about radiation exposure associated with the consequent cancer particularly in children. We assessed validity of previous large prospective study named Pediatric Emergency Care Applied Research Network (PECARN) retrospectively to determine the necessity of CT scans for children younger than 2 years with minor head injury. Methods We reviewed medical records of children younger than 2 years discharged from our emergency department with S00–09 diagnosis code of ICD-10 from August 2008 to December 2014. Patients who had only soft tissue injury without blunt trauma, did not CT scan take brain CT, whose head trauma was not mild, and who was uncertain to meet the rule were excluded. All included patients were divided into the PECARN rule positive group and negative group. Each group was compared by sensitivity, specificity, positive predictive value and negative predictive value to predict four outcomes of clinically important traumatic brain injury (ciTBI), abnormal CT findings, intracranial hemorrhage, and isolated simple skull fracture. Results A total of 1,491 patients were included, 656 PECARN rule positive and 835 negative patients. There is statistical difference between PECARN rule positive and negative the 2 group for ciTBI (P < 0.001), abnormal CT findings (P < 0.001), intracranial hemorrhage (P < 0.001), and isolated simple skull fracture (P < 0.001) with high sensitivity (100.0%, 89.5%, 91.7%,85.7%) and negative predictive value (100.0%, 99.3%, 99.6%, 99.6%). Conclusion We confirmed that PECARN rule is a useful tool to determine the necessity of CT scan and reduce unnecessary CT scan for children younger than 2 years with minor head injury

The dominant global modes of recent internal sea level variability

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(4), (2019):2750-2768, doi: 10.1029/2018JC014635.The advances in the modern sea level observing system have allowed for a new level of knowledge of regional and global sea level in recent years. The combination of data from satellite altimeters, Gravity Recovery and Climate Experiment (GRACE) satellites, and Argo profiling floats has provided a clearer picture of the different contributors to sea level change, leading to an improved understanding of how sea level has changed in the present and, by extension, may change in the future. As the overlap between these records has recently extended past a decade in length, it is worth examining the extent to which internal variability on timescales from intraseasonal to decadal can be separated from long‐term trends that may be expected to continue into the future. To do so, a combined modal decomposition based on cyclostationary empirical orthogonal functions is performed simultaneously on the three data sets, and the dominant shared modes of variability are analyzed. Modes associated with the trend, seasonal signal, El Niño–Southern Oscillation, and Pacific decadal oscillation are extracted and discussed, and the relationship between regional patterns of sea level change and their associated global signature is highlighted.The satellite altimetry grids are available from NASA JPL/PO.DAAC at the following location: https://podaac.jpl.nasa.gov/dataset. GRACE land water storage data are available at http://grace.jpl.nasa.gov, supported by the NASA MEaSUREs Program. The gridded fields based on Argo data used to compute the steric sea level data are available at http://www.argo.ucsd.edu/Gridded_fields.html. The gridded fields based on Argo data used to compute the steric sea level data are available at http://www.argo.ucsd.edu/Gridded_fields.html. The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. B. D. H., F. W. L., J. T. R., and P. R. T. acknowledge support from NASA grant 80NSSC17K0564 (NASA Sea Level Change Team). C. G. P. acknowledges support from NSF awards OCE‐1558966 and OCE‐1834739. K. Y. K. was partially supported for this research by the National Science Foundation of Korea under the grant NRF‐ 2017R1A2B4003930.2019-09-2

The Dominant Global Modes of Recent Internal Sea Level Variability

The advances in the modern sea level observing system have allowed for a new level of knowledge of regional and global sea level in recent years. The combination of data from satellite altimeters, Gravity Recovery and Climate Experiment (GRACE) satellites, and Argo profiling floats has provided a clearer picture of the different contributors to sea level change, leading to an improved understanding of how sea level has changed in the present and, by extension, may change in the future. As the overlap between these records has recently extended past a decade in length, it is worth examining the extent to which internal variability on timescales from intraseasonal to decadal can be separated from long‐term trends that may be expected to continue into the future. To do so, a combined modal decomposition based on cyclostationary empirical orthogonal functions is performed simultaneously on the three data sets, and the dominant shared modes of variability are analyzed. Modes associated with the trend, seasonal signal, El Niño–Southern Oscillation, and Pacific decadal oscillation are extracted and discussed, and the relationship between regional patterns of sea level change and their associated global signature is highlighted

Decadal variability of the upper ocean heat content in the East/Japan Sea and its possible relationship to northwestern Pacific variability

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C02017, doi:10.1029/2011JC007369.The upper ocean heat content variability in the East/Japan Sea was investigated using a 40 year temperature and salinity data set from 1968 to 2007. Decadal variability was identified as the dominant mode of variability in the upper ocean (0–300 m) aside from the seasonal cycle. The decadal variability is strong to the west of northern Honshu, west of the Tsugaru Strait, and west of southern Hokkaido. Temperature anomalies at 50–125 m exhibit a large contribution to the decadal variability, particularly in the eastern part of the East/Japan Sea. The vertical structure of regressed temperature anomalies and the spatial patterns of regressed 10°C isotherms in the East/Japan Sea suggest that the decadal variability is related to upper ocean circulation in the East/Japan Sea. The decadal variability also exhibits an increasing trend, which indicates that the regions showing large decadal variations experienced warming on decadal time scales. Further analysis shows that the decadal variability in the East/Japan Sea is not locally isolated but is related to variability in the northwestern Pacific.This work was supported by grants from the Ministry of Land, Transport, and Maritime Affairs, Korea (Ocean Climate Variability Program and EAST-I Project).2012-08-0