Alfred Powell

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Papers by Alfred Powell

Use of SSU/MSU Satellite Observations to Validate Upper Atmospheric Temperature Trends in CMIP5 Simulations

Remote Sensing, 2015

The tropospheric and stratospheric temperature trends and uncertainties in the fifth Coupled Mode... more The tropospheric and stratospheric temperature trends and uncertainties in the fifth Coupled Model Intercomparison Project (CMIP5) model simulations in the period of 1979-2005 have been compared with satellite observations. The satellite data include those from the Stratospheric Sounding Units (SSU), Microwave Sounding Units (MSU), and the Advanced Microwave Sounding Unit-A (AMSU). The results show that the CMIP5 model simulations reproduced the common stratospheric cooling (´0.46-´0.95 K/decade) and tropospheric warming (0.05-0.19 K/decade) features although a significant discrepancy was found among the individual models being selected. The changes of global mean temperature in CMIP5 simulations are highly consistent with the SSU measurements in the stratosphere, and the temporal correlation coefficients between observation and model simulations vary from 0.6-0.99 at the 99% confidence level. At the same time, the spread of temperature mean in CMIP5 simulations increased from stratosphere to troposphere. Multiple linear regression analysis indicates that the temperature variability in the stratosphere is dominated by radioactive gases, volcanic events and solar forcing. Generally, the high-top models show better agreement with observations than the low-top model, especially in the lower stratosphere. The CMIP5 simulations underestimated the stratospheric cooling in the tropics and overestimated the cooling over the Antarctic compared to the satellite observations. The largest spread of temperature trends in CMIP5 simulations is seen in both the Arctic and Antarctic areas, especially in the stratospheric Antarctic.

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S4: An O2R/R2O Infrastructure for Optimizing Satellite Data Utilization in NOAA Numerical Modeling Systems: A Step Toward Bridging the Gap between Research and Operations

Bulletin of the American Meteorological Society, 2016

In 2011, the National Oceanic and Atmospheric Administration (NOAA) began a cooperative initiativ... more In 2011, the National Oceanic and Atmospheric Administration (NOAA) began a cooperative initiative with the academic community to help address a vexing issue that has long been known as a disconnection between the operational and research realms for weather forecasting and data assimilation. The issue is the gap, more exotically referred to as the “valley of death,” between efforts within the broader research community and NOAA’s activities, which are heavily driven by operational constraints. With the stated goals of leveraging research community efforts to benefit NOAA’s mission and offering a path to operations for the latest research activities that support the NOAA mission, satellite data assimilation in particular, this initiative aims to enhance the linkage between NOAA’s operational systems and the research efforts. A critical component is the establishment of an efficient operations-to-research (O2R) environment on the Supercomputer for Satellite Simulations and Data Assimi...

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A Comparison of Snowpack Properties Derived from SSM/I Emissivity Data with Snowpack Properties Derived from SSM/I Brightness Temperature Data

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

Snowpack properties highly influence the microwave scattering. Brightness temperature from SSM/I ... more Snowpack properties highly influence the microwave scattering. Brightness temperature from SSM/I has the effect of atmosphere especially in high frequency channels. Microwave emissivities, which have been derived by removing the contribution of the atmosphere, clouds, and rain, can also be used to estimate snowpack properties. In order to improve microwave based Snow Water Equivalent (SWE) retrievals, snow pack properties variations

Extreme events of stratospheric stationary waves and indications for stratosphere–troposphere coupling: simultaneous analysis in boreal winter

Theoretical and Applied Climatology, 2014

Using monthly stratospheric geopotential height at 20 hPa derived from the National Centers for E... more Using monthly stratospheric geopotential height at 20 hPa derived from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis datasets, a planetary wave amplitude index (PWAI) is defined by wave numbers (WN) 1-3 over 55-75°N to indicate the strength of the stratospheric stationary waves. The vertical variability of the stratospheric stationary waves and their possible connection with the stratosphere-troposphere coupling have been investigated in the North Hemisphere winter [December-February (DJF)] for the period of 1950-2010. In terms of the stratospheric PWAI, a pair of bipolar extreme (strong and weak) stratospheric wave events is identified based on the top-ten principle. The comparisons of composite analysis for the bipolar events show that the stratospheric PWAI is an effective indicator for the dynamic coupling between the stratosphere and troposphere in the boreal winter. The results show that the opposite response in the stationary wave activity, atmospheric circulations, precipitation, and surface temperature is not only found in the stratosphere but also in the troposphere and surface. In the stratospheric top-ten extremely strong (strong10) events, the wave amplitude, poleward momentum, and heat fluxes in zonal WN1 tend to increase in the whole atmospheric layer from the stratosphere down to the surface. The polar vortex is enhanced in the stratosphere and reduced in the troposphere. Both the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO) tend to a positive phase with the sea-level pressure (SLP) decreasing in the high latitudes and increasing in the mid-low latitudes. The precipitation tends to increase in the southern Asia and decrease in the southern Europe. The surface temperature becomes warmer in the middle of the Asian-European continent and cooler in southwest Asia and south Europe. In contrast, there is a clear opposing behavior except for a few small areas during the stratospheric top-ten extremely weak (weak10) events.

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GSI/WRF Regional Data Assimilation System and Its Application in the Weather Forecasts over Southwest Asia

Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications (Vol. II), 2013

In this study, the impact of directly assimilating Advanced TIROS Operational Vertical Sounder (A... more In this study, the impact of directly assimilating Advanced TIROS Operational Vertical Sounder (ATOVS) radiances using the Community Radiative Transfer Model (CRTM) was evaluated to determine the impact on forecasts over Southwest Asia. The CRTM was developed by the Center for Satellite Applications and Research (STAR) and its application was promoted by the Joint Center for Satellite Data Assimilation (JCSDA). The ATOVS radiance data from the National Environmental Satellite Data and Information Service (NESDIS), the Gridpoint Statistical Interpolation (GSI) three-dimensional variational analysis (3DVAR) system from the National Centers for Environmental Prediction (NCEP), and the Advanced Research WRF (WRF-ARW) model from the National Center for Atmospheric Research (NCAR) were employed in this study.First, this paper will describe the forecasting errors encountered from running the WRF-ARW model in the complex terrain of Southwest Asia from 1–31 May 2006. The subsequent statistical evaluation is designed to assess the model’s surface and upper-air forecast accuracy. The results show that the model biases caused by inadequate parameterizations of physical processes are relatively small, except for the 2-m temperature, as compared to the nonsystematic errors resulting in part from the uncertainty in initial conditions. The total model forecast errors at the surface show a substantial spatial heterogeneity and the errors are relatively larger in higher elevation mountain areas. The performance of 2-m temperature forecasts is different from the other surface variables’ forecasts; the model forecast errors in 2-m temperature forecasts are closely related to the terrain configuration. The simulated diurnal variation of near-surface temperature is much smaller than the observed diurnal variation.Second, to understand the impact of initial conditions on the accuracy of the model forecasts, the satellite radiances are assimilated into the numerical model through GSI data assimilation system. The results indicate that on average over a 30-day experiment for the 24- and 48-h (second 24-h) forecasts, the satellite data provides beneficial information for improving the initial conditions and the model errors are reduced to some degree over some of the study locations. The diurnal cycle of some forecast variables can be improved by using adequate initial conditions with satellite radiance data assimilation.

Analysis of the Effects of Snowpack Properties on Satellite Microwave Brightness Temperature and Emissivity Data

Journal of Geophysics & Remote Sensing, 2012

Spatial variations of snowpack properties are an essential component in flood predictions and wat... more Spatial variations of snowpack properties are an essential component in flood predictions and water resource management. Satellite microwave remote sensing has shown great potential in retrieving snowpack properties such as: snow depth, snow grain size, and snow density. In this research, we investigate the potential of microwave emissivity which is highly influenced by snowpack properties. Brightness temperature and emissivity data generated from HUT (Helsinki University of Technology) microwave emission of snow model were evaluated with satellite microwave measurements. The comparison of the real measurements (in-situ and satellite) with the modeled results shows that the scattering signature (19GHz-37GHz and 19GHz-85GHz) shows better results in emissivities rather than brightness temperature data. Furthermore, the over the deep snow (>30cm), the emissivities scattering signature of (19GHz-37GHz) has best performance while over shallow snow (<30cm) the emissivities scattering signature of (19GHz-85GHz) performs superior. The results indicate the validity of grain growth assumption to some extent but it fails to address it quantitatively as a function of time.

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Two mechanisms responsible for marine ecosystem regime shifts from fish landings data off the West Coast of California (WCC)

Natural Science, 2013

This investigation focuses on two mechanisms over the North Pacific connecting decadal regime shi... more This investigation focuses on two mechanisms over the North Pacific connecting decadal regime shifts to regional ecosystem impacts. The physical conditions show the impacts of the atmospheric surface wind stress and the sea surface temperature (SST) physical conditions on the fish landings along the west coast of California (WCC) from 1928-2008. The two mechanisms are identified by the two types of wind stress (e.g. westerly-easterly; or cyclonic-anticyclonic) anomaly over the central North Pacific which results in SST anomalies in the WCC. In both mechanism cases, the local warm (cold) SST anomaly leads to the number of fish species rising (falling) in the WCC region. In addition, the wind stress and SST anomaly pattern over the North Pacific is closely related to the intensity of the regime shifts as identified in the fish landings off the WCC.

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Regime Shifts in the Atmosphere and Their Relationship to Abrupt Ocean Changes

Use of Satellite and in-Situ Data To Improve Sustainability, 2009

... Keywords Abrupt ocean change • Fish stock • El Nino/La Nina • Global waves Introduction ... A... more

Uncertainty estimation of the global temperature trends for multiple radiosondes, reanalyses, and CMIP3/IPCC climate model simulations

Theoretical and Applied Climatology, 2011

Based on three groups of datasets that include radiosondes, reanalyses, and climate model simulat... more Based on three groups of datasets that include radiosondes, reanalyses, and climate model simulations (e.g., Coupled Model Intercomparison Project, CMIP3) from 1979 to 2008, the interannual variability, global temperature trends, and their uncertainty using ensemble spread among intra-group and inter-group datasets have been discussed. The results show that the interannual temperature variability increased from the troposphere to stratosphere, and the maximum occurs around 50 hPa. The CMIP3 climate models have the largest discrepancy in the stratosphere. The intra-group correlations at 500 hPa generally show high similarity within each data group while the inter-group correlations between reanalyses and the CMIP3 climate model simulations indicate lesser similarity. In contrast, the inter-group correlation at 50 hPa is improved except with the Japanese 25-year Reanalysis Project (JRA-25) dataset, and the Twentieth Century Reanalysis (20CR) reanalysis shows a weak cross correlation. The global temperature trends are highly dependent on the individual data sources. Compared to the radiosondes, the reanalyses show a large ensemble spread of trends in the stratosphere, and the CMIP3 climate model simulations have a large ensemble spread in the height of the crossover point where tropospheric warming changes into stratospheric cooling. The largest ensemble spread among the reanalyses in the stratosphere is mainly from the large discrepancy in the JRA-25 reanalysis after 1998 and a relatively weak anomaly in the 20CR before 1986. The largest ensemble spread among the CMIP3 climate models in the troposphere is related to the influence of both volcanic eruptions and El Niño/La Niña-Southern Oscillation events. The strong anomalies corresponding to the volcanic eruptions of El Chichon in 1982 and Mt Pinatubo in 1991 are clearly identified in the stratosphere. These volcanic eruptions reduced the warming in the troposphere and strengthened the cooling in the stratosphere during the most recent 30 years.

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A new assessment of the mid-1970s abrupt atmospheric temperature change in the NCEP/NCAR reanalysis and associated solar forcing implications

Theoretical and Applied Climatology, 2010

Based on the reanalysis data from the National Centers for Environmental Prediction and National ... more Based on the reanalysis data from the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP–NCAR) and solar radio irradiance (SRI) at 10.7 cm wavelength obtained from the National Oceanic and Atmospheric Administration’s Space Weather Prediction center, the abrupt temperature change in the mid-1970s and its possible association with solar irradiance variability have been investigated. The results show

Protestant Work Ethic Endorsement and Social Justice Values in Developing and Developed Societies: Comparing Jamaica and New Zealand

Psychology & Developing Societies, 2009

Taking Weber's Protestant Ethic and the Spirit of Capitalism thesis as the point of departure... more Taking Weber's Protestant Ethic and the Spirit of Capitalism thesis as the point of departure, this paper compares work ethic endorsement patterns and social justice correlates in a developing society, Jamaica, and a developed society, New Zealand. A condensed version of Mirels and Garrett's Protestant work ethic scale and related demographic and social values-related measures were administered at Jamaican and New Zealand universities. High and low Protestant ethic (PE) clusters were isolated, within each culture, among comparable samples of undergraduate social science students, and multiple analysis of variance applied to test effects of culture, Protestant religious affiliation and related “social justice values” variables (welfare state support, redistribution, intergenerational equity, free enterprise, social distance from the disadvantaged, social Darwinism). Results suggest there are significant cultural differences between high and low PE scorers on key justice-relat...

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Book Reviews: Christopher Beem, The Necessity of Politics: Reclaiming American Public Life (Chicago: University of Chicago Press, 1999), pp. 256, US$28

Political Science, 2000

It has now been two decades since the Thatcher-Reagan backlash against the twentieth century welf... more It has now been two decades since the Thatcher-Reagan backlash against the twentieth century welfarc state first gained a foothold in western democracies. In that time the concept of ’civil society’ has increasingly been appropriated by conservatives and New Right intellectuals to justify dismantling redistributive government programmes and to avoid ’political’ solutions to a variety of modern social problems. The works of Milton Friedman, Michael Novak, Friederich Hayek, Gertrude Himmelfarh. and Robert Bork come to mind as prominent examples of essentially anti-statist and/or anti-political interpretations of the civil society idea. The appeal of civil society rationales has been particularly fertilc in the United States, where they resonate easily with historically-dominant cultural premises of Lockean individualism, self-reliance, private enterprise, ’limited government’, and voluntarism. Since colonial times America has been a society with a stubborn preference for responding to the needs of its citizens through private voluntary associations which would mediate between the individual and society without t

Exploring the Multidimensional Nature of Distributive Justice Perception: The Challenge for Cross-Cultural Psychology

Journal of Cross-Cultural Psychology, 2005

DOI: 10.1177/0022022104271423 2005 36: 9 Journal of Cross-Cultural Psychology Lawrence Alfred Pow... more

CREST-Snow Field Experiment: analysis of snowpack properties using multi-frequency microwave remote sensing data

Hydrology and Earth System Sciences, 2013

The CREST-Snow Analysis and Field Experiment (CREST-SAFE) was carried out during winter 2011 at t... more The CREST-Snow Analysis and Field Experiment (CREST-SAFE) was carried out during winter 2011 at the research site of the National Weather Service office, Caribou ME, USA. In this ground experiment, dual polarized microwave (37 and 89 GHz) observations are conducted along with detailed synchronous observations of snowpack properties. The objective of this long term field experiment is to improve our understanding of the effect of changing snow characteristics (grain size, density, temperature) under various meteorological conditions on the microwave emission of snow and hence to improve retrievals of snow cover properties from satellite observations in the microwave spectral range. In this paper, we presented the overview of field experiment and preliminary analysis of the microwave observations for the first year of experiment along with support observations of the snowpack properties obtained during the 2011 winter season. SNTHERM and HUT (Helsinki University of Technology) snow emission model were used to simulate snowpack properties and microwave brightness temperatures respectively. Simulated brightness temperatures were compared with observed HESSD 9, 8105-8136, 2012 CREST-Snow Field Experiment: analysis of snowpack properties T. Lakhankar et al.

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Predicting natural disasters in the coastal zone based on links between land and marine ecosystems

Geomatics, Natural Hazards and Risk, 2010

The Normalized Difference Vegetation Index (NDVI) was used for the analysis of ecological charact... more The Normalized Difference Vegetation Index (NDVI) was used for the analysis of ecological characteristics of the northwestern Black Sea region, which includes significant coastal territories and sea water areas along the northwest coast of the Black Sea. In the present study the following data were used: (1) NDVI and Vegetation Health Index (VHI) spatial distribution data for the period 1997-2008 for southern areas of the Ukraine around the Black Sea (prepared in the USA from NOAA's GVI2 dataset), (2) 1998-2008 NDVI data derived from MODIS (Aqua and Terra) visible channels and SeaWiFS scanners. It is shown that in the integrated land-marine ecosystem in the coastal zone, NDVI can be used as an indicator for hazards such as hypoxia, hydrosulphuric infection and eutrophication.

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Dynamical downscaling precipitation over Southwest Asia: Impacts of radiance data assimilation on the forecasts of the WRF-ARW model

Atmospheric Research, 2012

Based on the dynamical downscaling with the Advanced Research Weather (WRF-ARW) mesoscale model, ... more Based on the dynamical downscaling with the Advanced Research Weather (WRF-ARW) mesoscale model, the accuracy of the precipitation forecasts in Southwest Asia has been assessed. Results show that the accuracy of the 24-h and 48-h forecasts for precipitation is closely related to the complex topography of the mountain areas. To understand the impacts of the initial condition uncertainties on accuracy of the dynamical downscaling, a series of data assimilation experiments has been performed. The Advanced Television and Infrared Observation Satellite Operational Vertical Sounder (ATOVS) radiance observations and a data assimilation system named the Gridpoint Statistical Interpolation (GSI), developed by the National Centers for Environmental Prediction (NCEP), were used in this study. The results show that the satellite data provides beneficial information for improving the initial conditions for the dynamical model system and the "forecast" errors are reduced for most locations within the 24-h hindcasts.

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Analysis of Snowpack Properties and Estimation of Snow Grain Size using CLPX Data

IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008

... Dugwon Seo 1 , Amir E Azar 1 , Reza Khanbilvardi 1 and Al Powell 2 ... signatures [2]. One of... more

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