@article{cheng_wang-li_classen_bloomfield_2022, title={Performance of a Thermodynamic Model for Predicting Inorganic Aerosols in the Southeastern U.S.}, volume={13}, ISSN={2073-4433}, url={http://dx.doi.org/10.3390/atmos13121977}, DOI={10.3390/atmos13121977}, abstractNote={Fine particulate matter (i.e., PM2.5) has gained intensive attention due to its adverse health and visibility degradation effects. As a significant fraction of atmospheric PM2.5, secondary inorganic PM2.5 may be formed through the gas-phase ammonia (NH3) and particle-phase ammonium (NH4+) partitioning. While partitioning of NH3-NH4+ may be simulated using a thermodynamic equilibrium model, disagreement between model predictions and measurements have been realized. In addition, the applicability of the model under different conditions has not been well studied. This research aims to investigate the applicability of a thermodynamic equilibrium model, ISORROPIA II, under different atmospheric conditions and geographic locations. Based upon the field measurements at the Southeastern Aerosol Research and Characterization (SEARCH) network, the performance of ISORROPIA II was assessed under different temperature (T), relative humidity (RH), and model setups in urban and rural locations. The impact of organic aerosol (OA) on the partitioning of NH3-NH4+ was also evaluated. Results of this research indicate that the inclusion of non-volatile cations (NVCs) in the model input is necessary to improve the model performance. Under high T (>10 °C) and low RH (<60%) conditions, ISORROPIA II tends to overpredict nitric acid (HNO3) concentration and underpredict nitrate (NO3−) concentration. The predominance of one phase of semi-volatile compound leads to low accuracy in the model prediction of the other phase. The model with stable and metastable setups may also perform differently under different T-RH conditions. Metastable model setup might perform better under high T (>10 °C) and low RH (<60%) conditions, while stable model setup might perform better under low T (<5 °C) conditions. Both model setups have consistent performance when RH is greater than 83%. Future studies using ISORROPIA II for the prediction of NH3-NH4+ partitioning should consider the inclusion of NVCs, the under/over prediction of NO3−/HNO3, the selection of stable/metastable model setups under different T-RH conditions, and spatiotemporal variations of inorganic PM2.5 chemical compositions.}, number={12}, journal={Atmosphere}, publisher={MDPI AG}, author={Cheng, Bin and Wang-Li, Lingjuan and Classen, John and Bloomfield, Peter}, year={2022}, month={Nov}, pages={1977} }
 @article{cheng_wang-li_meskhidze_classen_bloomfield_2021, title={Partitioning of NH3-NH4+ in the Southeastern U.S.}, volume={12}, ISSN={2073-4433}, url={http://dx.doi.org/10.3390/atmos12121681}, DOI={10.3390/atmos12121681}, abstractNote={The formation of inorganic fine particulate matter (i.e., iPM2.5) is controlled by the thermodynamic equilibrium partitioning of NH3-NH4+. To develop effective control strategies of PM2.5, we aim to understand the impacts of changes in different precursor gases on iPM2.5 concentrations and partitioning of NH3-NH4+. To understand partitioning of NH3-NH4+ in the southeastern U.S., responses of iPM2.5 to precursor gases in four seasons were investigated using field measurements of iPM2.5, precursor gases, and meteorological conditions. The ISORROPIA II model was used to examine the effects of changes in total ammonia (gas + aerosol), total sulfuric acid (aerosol), and total nitric acid (gas + aerosol) on iPM2.5 concentrations and partitioning of NH3-NH4+. The results indicate that reduction in total H2SO4 is more effective than reduction in total HNO3 and total NH3 to reduce iPM2.5 especially under NH3-rich condition. The reduction in total H2SO4 may change partitioning of NH3-NH4+ towards gas-phase and may also lead to an increase in NO3− under NH3-rich conditions, which does not necessarily lead to full neutralization of acidic gases (pH < 7). Thus, future reduction in iPM2.5 may necessitate the coordinated reduction in both H2SO4 and HNO3 in the southeastern U.S. It is also found that the response of iPM2.5 to the change in total H2SO4 is more sensitive in summer than winter due to the dominance of SO42− salts in iPM2.5 and the high temperature in summer. The NH3 emissions from Animal Feeding Operations (AFOs) at an agricultural rural site (YRK) had great impacts on partitioning of NH3-NH4+. The Multiple Linear Regression (MLR) model revealed a strong positive correlation between cation-NH4+ and anions-SO42− and NO3−. This research provides an insight into iPM2.5 formation mechanism for the advancement of PM2.5 control and regulation in the southeastern U.S.}, number={12}, journal={Atmosphere}, publisher={MDPI AG}, author={Cheng, Bin and Wang-Li, Lingjuan and Meskhidze, Nicholas and Classen, John and Bloomfield, Peter}, year={2021}, month={Dec}, pages={1681} }
 @article{cheng_wang-li_classen_meskhidze_bloomfield_2021, title={Spatial and temporal variations of atmospheric chemical condition in the Southeastern U.S.}, volume={248}, ISSN={0169-8095}, url={http://dx.doi.org/10.1016/j.atmosres.2020.105190}, DOI={10.1016/j.atmosres.2020.105190}, abstractNote={Animal feeding operations (AFOs) are the largest ammonia (NH3) emission sources in the United States (U.S.). However, the impact of NH3 emissions from AFOs on the formation of secondary inorganic PM2.5 (iPM2.5) has not been well understood and systematically assessed. Under the Southeastern Aerosol Research and Characterization (SEARCH) Network, the hourly concentrations of iPM2.5 chemical compositions and its precursor gases as well as meteorological data were measured at eight urban/nonurban sites labeled as JST/YRK, BHM/CTR, GFP/OAK, and PNS/OLF during 1998–2016. Using the SEARCH data, this research investigated the spatiotemporal variations of atmospheric chemical conditions in those rural and urban areas. The spatiotemporal variations of atmospheric chemical conditions at the eight sites are characterized by four parameters, including (1) gas ratio (GR), (2) gas-phase NH3 molar fraction (NH3/NHx), (3) total available NH3 (gaseous ammonia + aerosol ammonium) to sulfate (SO42−) molar ratio (TA/TS), and (4) PM2.5 ammonium + nitrate to total PM2.5 mass ratio (AN/PM2.5). Results indicate that the NH3 emissions from AFOs may explain the greater values of GR, NH3/NHx, and TA/TS in the wind directions coming from AFOs at YRK and OAK rural sites than the other wind directions. In the wind directions coming from AFOs at YRK and OAK, NH3 was in excess of fully neutralizing acidic gases, more NH3 stayed in gas phase than those in other wind directions, and both ammonium sulfate and ammonium nitrate existed in iPM2.5. The upward trend in NH3/NHx indicates that gas-particle partitioning ofNH3–NH4+shifted toward gas phase, while the downward trend in AN/PM2.5 may implicate that smaller fraction of PM2.5 was directly NH3 sensitive. Understanding of the spatiotemporal variations of atmospheric chemical condition provides insights to improve our understanding of iPM2.5 formation under rural and urban conditions, the reduction in sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions resulted in the reduction of iPM2.5 formation despite the increase in NH3 emissions in the Southeastern U.S.}, journal={Atmospheric Research}, publisher={Elsevier BV}, author={Cheng, Bin and Wang-Li, Lingjuan and Classen, John and Meskhidze, Nicholas and Bloomfield, Peter}, year={2021}, month={Jan}, pages={105190} }
 @article{zhang_ma_brandao_kaber_bloomfield_swangnetr_2016, title={Biometric validation of a virtual reality-based psychomotor test for motor skill training}, volume={28}, ISSN={["1949-3614"]}, DOI={10.1080/10400435.2016.1165758}, abstractNote={ABSTRACT Psychomotor tests have been applied in clinical therapy and laboratory research as tools for evaluating motor and cognitive skills. Some studies have developed computerized versions of such tests using virtual reality (VR) systems with haptic interface controls. These systems allow for increased flexibility in test delivery and accuracy in performance assessment. In this study, a VR-based computer simulation of the block design (BD) test (a standardized psychomotor task as part of an adult IQ test) was developed and compared with the physical version of the test. Performance was evaluated based on four types of muscle activation collected using electromyography (EMG), time spent in completing the task, and subjective ratings of workload. Results verified the VR-based task as physically comparable to the conventional BD test. The validated computerized psychomotor task may be applied for both experimental and clinical use in future studies.}, number={4}, journal={ASSISTIVE TECHNOLOGY}, author={Zhang, Wenjuan and Ma, Wenqi and Brandao, Maicom and Kaber, David B. and Bloomfield, Peter and Swangnetr, Manida}, year={2016}, pages={233–241} }
 @inproceedings{zhang_swangnetr_bloomfield_kaber_2016, title={Electromyography (EMG) as a tool for computerized psychomotor test validation}, volume={489}, booktitle={Advances in physical ergonomics and human factors}, author={Zhang, W. J. and Swangnetr, M. and Bloomfield, P. and Kaber, D.}, year={2016}, pages={967–978} }
 @article{xiao_ku_bloomfield_ghosh_2015, title={On the degrees of freedom in MCMC-based Wishart models for time series data}, volume={98}, ISSN={["1879-2103"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84920930486&partnerID=MN8TOARS}, DOI={10.1016/j.spl.2014.12.012}, abstractNote={The Wishart distribution has long been a useful tool for modeling covariance structures. According to Gyndikin’s theorem, the degrees of freedom (df) for a Wishart distribution can be any real number belonging to the Gyndikin set, either integer-valued or fractional. However, the fractional-df versioned Wishart distribution has received only limited attention, which may lead to inaccurate implementation in practice. This paper shows by a numerical example that, when implementing Markov chain Monte Carlo (MCMC) methods in Wishart models for time series data, the lack of attention to the fractional df where necessary can result in seriously biased posterior estimation due to the compounding errors caused by the time dependency assumption. We further conduct a sensitivity analysis to explain why the seemingly small difference between the integer-valued df and the fractional df leads to very different outcomes.}, journal={STATISTICS & PROBABILITY LETTERS}, author={Xiao, Yuewen and Ku, Yu-Cheng and Bloomfield, Peter and Ghosh, Sujit K.}, year={2015}, month={Mar}, pages={59–64} }
 @article{ku_bloomfield_ghosh_2014, title={A flexible observed factor model with separate dynamics for the factor volatilities and their correlation matrix}, volume={14}, ISSN={["1477-0342"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84893546299&partnerID=MN8TOARS}, DOI={10.1177/1471082x13490016}, abstractNote={ In this article, we consider a novel regression model with observed factors. To allow for the prediction of future observations, we model the observed factors using a flexible multivariate stochastic volatility (MSV) structure with separate dynamics for the volatilities and the correlation matrix. The correlation matrix of the factors is time varying, and its evolution is described by an inverse Wishart process. We develop an estimation procedure based on Bayesian Markov chain Monte Carlo methods, which has two major advantages compared to existing methods for similar models in the literature. First, the procedure is computationally more efficient. Second, it can be applied to calculate the predictive distributions for future observations. We compare the proposed model with other multivariate volatility models using Fama-French factors and portfolio weighted return data. The result shows that our model has better predictive performance. }, number={1}, journal={STATISTICAL MODELLING}, author={Ku, Yu-Cheng and Bloomfield, Peter and Ghosh, Sujit K.}, year={2014}, month={Feb}, pages={1–20} }
 @article{li_wang-li_shah_jayanty_bloomfield_2014, title={Ammonia concentrations and modeling of inorganic particulate matter in the vicinity of an egg production facility in Southeastern USA}, volume={21}, ISSN={["1614-7499"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84895876258&partnerID=MN8TOARS}, DOI={10.1007/s11356-013-2417-z}, abstractNote={Ammonia (NH3) is an important base gas and can react with acidic species to form atmospheric aerosols. Due to the rapid growth of poultry and swine production in the North Carolina Coastal Plain, atmospheric NH3 concentrations across the region have subsequently increased. Ammonia concentrations and inorganic particulate matter (PM) at four ambient stations in the vicinity of an egg production facility were measured for 1 year using PM2.5 speciation samplers with honeycomb denuders and ion chromatography (IC). Meanwhile, concentrations of NH3 and inorganic PM in one of the egg production houses were also simultaneously measured using a gas analyzer for NH3 and the filter pack plus IC method for inorganic PM. An equilibrium model-ISORROPIA II was applied to predict the behavior of inorganic aerosols in response to precursor gas concentrations and environmental parameters. Average ambient NH3 concentrations varied from 10.0 to 27.0 μg/m(3), and they were negatively correlated with the distances from the ambient location to the nearest egg production house exhausts. Ambient NH3 concentrations were higher in warm seasons than in cold seasons. Measured NH3 concentrations agreed well with ISORROPIA II model predictions at all sampling stations. For the ambient stations, there was a good agreement in particle phase NH4 (+) between the model simulation and observations. For the in-house station, the model simulation was applied to correct the overestimation of particle phase NH4 (+) due to gas phase NH3 breaking through the denuders. Changes in SO4 (2-), NO3 (-), and Cl(-) yield proportional changes in inorganic PM mass. Due to the abundance of NH3 gas in the vicinity area of the monitored farm, changes in NH3 concentrations had a small effect on inorganic PM mass. Aerosol equilibrium modeling may be used to assess the influence of precursor gas concentrations on inorganic PM formation when the measurements for some species are unavailable.}, number={6}, journal={ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH}, author={Li, Qian-Feng and Wang-Li, Lingjuan and Shah, Sanjay B. and Jayanty, R. K. M. and Bloomfield, Peter}, year={2014}, month={Mar}, pages={4675–4685} }
 @article{huntsinger_rouphail_bloomfield_2013, title={Trip Generation Models Using Cumulative Logistic Regression}, volume={139}, ISSN={["0733-9488"]}, DOI={10.1061/(asce)up.1943-5444.0000151}, abstractNote={This paper evaluates the usefulness of the cumulative logistic regression model for estimating trip generation. The cumulative logistic regression model is a type of discrete choice model that estimates relationships between an ordered dependent variable, for example, person trip generation, and a set of independent variables, for example, household size, income, and workers. In addition to testing the model form, life cycle, area type, and accessibility variables are evaluated along with a set of widely used explanatory variables. A secondary focus of this paper is on the issue of temporal stability. Temporal stability is concerned with how models developed during one period of time transfer to a future period. The evaluation includes models based on widely used explanatory variables in addition to models supplemented with life cycle, area type, and accessibility variables to evaluate whether these variables result in improved stability. Analysis includes models estimated using 1995 survey data, applied using 2006 socioeconomic data, and evaluated against 2006 observed data. The results of this analysis show that cumulative logistic regression models are good candidate models for estimating trip generation and for improving the temporal stability of the model results. With respect to life cycle, area type, and accessibility, this research shows that there is benefit in including these variables to help explain trip making and to improve temporal stability.}, number={3}, journal={JOURNAL OF URBAN PLANNING AND DEVELOPMENT}, author={Huntsinger, Leta F. and Rouphail, Nagui M. and Bloomfield, Peter}, year={2013}, month={Sep}, pages={176–184} }
 @article{li_wang-li_shah_jayanty_bloomfield_2011, title={Fine particulate matter in a high-rise layer house and its vicinity}, volume={54}, number={6}, journal={Transactions of the ASABE}, author={Li, Q. and Wang-Li, L. and Shah, S. B. and Jayanty, R. K. M. and Bloomfield, P.}, year={2011}, pages={2299–2310} }
 @article{suh_chun_berger_bloomfield_2010, title={Distribution of Fiber Intersections in Two-Dimensional Random Fiber Webs - A Basic Geometrical Probability Model}, volume={80}, ISSN={["1746-7748"]}, DOI={10.1177/0040517509105071}, abstractNote={ Fundamental theories governing the number of fiber intersections in random nonwoven fiber webs were developed based on the planar geometry of fiber midpoints distributed in a two-dimensional Poisson field. First, the statistical expectation and variance for the number of fiber intersections in unit web area were obtained as functions of a fixed number of fibers with equal lengths. The theories were extended to the case of a two-dimensional Poisson field by assuming that the number and locations of the fibers are random. The theories are validated by a newly developed computer simulation method employing the concept of “seeding region” and “counting region.” Unlike all previously published papers, it was shown for the first time that the expectations and variances obtained theoretically matched that from computer simulations almost perfectly, validating both the theories and simulation algorithms developed. }, number={4}, journal={TEXTILE RESEARCH JOURNAL}, author={Suh, Moon W. and Chun, Heuiju and Berger, Roger L. and Bloomfield, Peter}, year={2010}, month={Mar}, pages={301–311} }
 @article{chen_bloomfield_fu_2003, title={An evaluation of alternative forecasting methods to recreation visitation}, volume={35}, ISSN={["0022-2216"]}, DOI={10.1080/00222216.2003.11950005}, abstractNote={This study examines the advantages and disadvantages of basic, intermediate, and advanced methods for visitor use forecasting where seasonality and limited data are characteristics of the estimation problem. The monthly use rates at the Milwaukee County Zoo, Wisconsin are used to illustrate the seasonal time series techniques. Forecasting methods include the Naive 1, Naive 2, single moving average (SMA) with the classical decomposition procedure, single exponential smoothing (SES), double exponential smoothing (DES), Winter's, and the seasonal autoregressive integrated moving average (SARIMA). The variation in visitor rates over the years makes the visitation trend for the Milwaukee County Zoo appealing in this empirical application. The series ranges from January 1981 through December 1999, a total of 228 months. The last 12, 24, or 60 months of those data are excluded from the original analysis, and used to evaluate the various methods. SARIMA and SMA with the classical decomposition procedure are found to be roughly equivalent in performance, as judged by modified mean absolute percentage error (MAPE) and modified root mean square percentage error (RMSPE) values of a longer estimation period with shorter period ahead forecasts. This study also finds that the SMA with classical decomposition method is more accurate than other techniques when a shorter estimation period with longer period ahead forecasts are included. While this study may not speak to all users of leisure related data, it serves as a comparative reference for those who seek guidance in deciding among a set of forecasting tools.}, number={4}, journal={JOURNAL OF LEISURE RESEARCH}, author={Chen, RJC and Bloomfield, P and Fu, JS}, year={2003}, pages={441–454} }
 @article{morgan_casey_easton_creech_ni_yoon_anderson_qualls_crosby_macpherson_et al._2003, title={Frequent sampling reveals dynamic responses by the transcriptome to routine media replacement in HepG2 cells}, volume={31}, ISSN={["1533-1601"]}, DOI={10.1080/01926230390213784}, abstractNote={ Cultured cell lines are employed extensively for biological research. Large-scale differential gene expression (LSDGE) is being used to study mechanisms of toxicity in such cultures. `Normal' gene expression dynamics could have a major impact on the design and interpretation of these studies. In order to provide understanding of such dynamics, we investigated LSDGE responses to media replacement in human hepatoblastoma cells (HepG2) using 5-minute sampling frequencies for 6 hours post routine media replacement. Each mRNA transcript was found to exhibit a characteristic `operating range' based on signal intensity. Following media replacement, which replenishes nutrients (eg, glucose and glutamate) and removes excretory products (eg, lactate), a complex set of gene expression changes was observed. Some transcripts appeared to switch on from a quiescent state to a very active one (eg, CYP1A1), others exhibited `clocklike' oscillations (eg, asparagine synthetase), or a synchronous burst (chirp) of expression up regulation (eg, timeless). Mathematical analysis (Fourier Transform, Singular Value Decomposition, Wavelets, Phase Analysis) of oscillating expression patterns identified cycle lengths ranging from 11.8 to 210 minutes. There were prominent 36.5- and 17.4-minute cycles, for subsets of genes, and transcript-specific differences in phase angle with respect to these cycles. The functional consequences of these novel observations remain to be determined. It is clear that dense time-course studies provide a valuable approach to the investigation of physiological responses to nutrients, toxicants, and other environmental variables. This research also highlights the need for an understanding of biological dynamics when using cell culture systems. }, number={4}, journal={TOXICOLOGIC PATHOLOGY}, author={Morgan, KT and Casey, W and Easton, M and Creech, D and Ni, H and Yoon, L and Anderson, S and Qualls, CW and Crosby, LM and MacPherson, A and et al.}, year={2003}, pages={448–461} }
 @book{bloomfield_2000, title={Fourier analysis of time series: An introduction.}, ISBN={0471889482}, DOI={10.1002/0471722235}, abstractNote={Note: Bibliogr. : p. 247-250. Index Reference Record created on 2004-09-07, modified on 2016-08-08}, publisher={New York: Wiley}, author={Bloomfield, P.}, year={2000} }
 @inbook{davis_eder_bloomfield_1998, title={Modeling ozone in the Chicago urban areas}, DOI={10.1007/978-1-4612-2226-2_2}, abstractNote={Ozone (O3) is a ubiquitous trace gas in the atmosphere. Its highest concentration is in the stratosphere, where it shields the earth’s surface from harmful ultraviolet radiation. At the surface, however, ozone is itself harmful, with destructive impacts on materials, crops, and health. Its levels have been high enough in certain areas to be of concern for several decades.}, booktitle={Case studies in environmental statistics}, publisher={New York: Springer}, author={Davis, J. M. and Eder, B. K. and Bloomfield, P.}, editor={D. Nychka, W. W. Piegorsch and Cox, L. H.Editors}, year={1998}, pages={5–26} }
 @inbook{davis_eder_bloomfield_1998, title={Regional and temporal models for ozone along the Gulf Coast}, DOI={10.1007/978-1-4612-2226-2_3}, abstractNote={The studies described in the previous chapter focused on estimating trends in a daily ozone summary having adjusted for the relationship of surface ozone concentrations to meteorology. Moreover, the analysis was largely restricted to the Chicago urban area. This chapter contrasts this narrow scope by studies that:}, booktitle={Case studies in environmental statistics}, publisher={New York: Springer}, author={Davis, J. M. and Eder, B. K. and Bloomfield, P.}, editor={D. Nychka, W. W. Piegorsch and Cox, L. H.Editors}, year={1998}, pages={27–50} }
 @article{mayewski_meeker_whitlow_twickler_morrison_bloomfield_bond_alley_gow_grootes_et al._1994, title={CHANGES IN ATMOSPHERIC CIRCULATION AND OCEAN ICE COVER OVER THE NORTH-ATLANTIC DURING THE LAST 41,000 YEARS}, volume={263}, ISSN={["0036-8075"]}, DOI={10.1126/science.263.5154.1747}, abstractNote={High-resolution, continuous multivariate chemical records from a central Greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41,000 years. These chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to Greenland [defined here as the polar circulation index (PCI)] and in the extent of ocean ice cover. Massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in PCI. During stadials without discharge events, ocean ice cover appears to reach some common maximum level. The massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling.}, number={5154}, journal={SCIENCE}, author={MAYEWSKI, PA and MEEKER, LD and WHITLOW, S and TWICKLER, MS and MORRISON, MC and BLOOMFIELD, P and BOND, GC and ALLEY, RB and GOW, AJ and GROOTES, PM and et al.}, year={1994}, month={Mar}, pages={1747–1751} }
 @article{bloomfield_nychka_1992, title={CLIMATE SPECTRA AND DETECTING CLIMATE CHANGE}, volume={21}, ISSN={["0165-0009"]}, DOI={10.1007/BF00139727}, number={3}, journal={CLIMATIC CHANGE}, author={BLOOMFIELD, P and NYCHKA, D}, year={1992}, month={Jul}, pages={275–287} }
 @article{stolarski_bloomfield_mcpeters_herman_1991, title={TOTAL OZONE TRENDS DEDUCED FROM NIMBUS 7 TOMS DATA}, volume={18}, ISSN={["0094-8276"]}, DOI={10.1029/91GL01302}, abstractNote={The Total Ozone Mapping Spectrometer (TOMS) on the Nimbus 7 satellite has been measuring the total column amount of ozone over the globe for more than 11 years. Recent improvements in the data analysis have led to a technique for determining and removing drift in the calibration such that the data at the end of the record are precise to ±1.3% (2σ) relative to the data at the beginning of the record. A statistical model, including terms for seasonal variation, linear trend, quasi‐biennial oscillation, solar cycle and second‐order autoregressive noise has been fit to the TOMS time series of total ozone data. The linear trend obtained when this statistical model is fit to the TOMS data averaged between 65N and 65S latitudes is −0.26±0.14%/year or −3% over the 11.6 year time period from November, 1978 through May, 1990. The trend is near zero (0.0002±0.2 %/year) at the equator and increases towards both poles. At 50N the annually averaged trend is −0.5±.21%/year. The 50N trend over the 11.6 year time period shows a strong seasonal variation from more than −0.8%/year in winter and early spring (February and March) to about −0.2%/year in summer (July and August).}, number={6}, journal={GEOPHYSICAL RESEARCH LETTERS}, author={STOLARSKI, RS and BLOOMFIELD, P and MCPETERS, RD and HERMAN, JR}, year={1991}, month={Jun}, pages={1015–1018} }