An Objective Procedure for Delineating the Circumpolar Vortex

The broad-scale, steering atmospheric circulation in the Northern Hemisphere, represented by the tropospheric circumpolar vortex (CPV), is an important driver of environmental processes. The area and circularity of the CPV are analyzed hereby delineating the leading edge of the CPV at the steepest 500-hPa geopotential height gradient globally. The daily CPV area and circularity were aggregated to monthly averages for contrast with measurements identified in previous research for the overlapping period of record (1979-2001). Accuracy of representation of the CPV is assessed through correlations to air-sea teleconnections known to be associated with broad-scale, extratropical steering circulation. Correlation to monthly teleconnection indices suggests that the new method allows for improvements in the calculation of area and circularity of the 500-hPa manifestation of the CPV. These improvements justify extension of the calculation of the standardized CPV area and circularity for the 1979-2017 period of record. Results largely mirror those for the shorter time series, with the Arctic Oscillation, North Atlantic Oscillation, and Pacific-North American teleconnection showing stronger links to CPV area and circularity than El Nino-Southern Oscillation and Pacific Decadal Oscillation. Collectively, these results suggest that the use of a singular indicator isohypse and/or monthly averaged data to represent the CPV may oversimplify analyses, especially for identifying past and future longwave ridges and troughs. This finding is important because the amplitudes and positions of the undulations in the broad-scale flow exert the most important impacts on variability at both low- and high-frequency time periods

Spatiotemporal Trends and Variability in the Centroid of the Northern Hemisphere\u27s Circumpolar Vortex

Recent previous research has established the sharpest gradient approach to defining the circumpolar vortex and has identified correlations of the area and circularity of the Northern Hemisphere\u27s circumpolar vortex (NHCPV) to important atmospheric-oceanic teleconnections. However, because geographical shifts in the NHCPV, independent of area or circularity changes, could affect surface environmental conditions, this research addresses the question of the extent to which the NHCPV centroid undergoes such shifts, both intra- and inter-annually. Results show that during the 1979-2017 period, the centroid has moved less on a daily basis in more recent years, perhaps indicative of a stabilization in circulation, with annual and semi-annual periodicities in the daily distance moved. A consistent preference toward the Eastern Hemisphere is evident by the displacement of the centroids toward the Pacific basin throughout the study period. Collectively, these results indicate the mid-tropospheric response to the near-surface warming. Plain Language Summary Our previous research developed an approach for delineating the leading edge of the boundary of the cold polar air circulation. This research identifies the position of the center of this polar circulation in the Northern Hemisphere, on a daily basis, from 1979 through 2017. We find that this centroid\u27s position has stabilized over time while maintaining a preferred position on the Eastern Hemisphere side of the North Pole. These results are important because they suggest that the middle-to-upper weather layer in the atmosphere may responding slowly to the near-surface warming over the last few decades

The Association Between Anticyclonic Weather Changes Over the Central Gulf Coast and Large-Scale Circulation Changes.

Trends in winter extratropical anticyclonic weather type frequencies (1961-1989) were examined for New Orleans, Louisiana, in order to identify the effects of global climatic change on regional-scale circulation changes over the central Gulf Coast. The number of days dominated by surface continental anticyclones (CH days) was found to have decreased significantly over time, while Pacific anticyclone (PH) frequency showed significant temporal increase. Therefore, 50 kPa geopotential height variability, 50 kPa geostrophic flow, and surface atmospheric variables were examined to determine whether changes in these features have accompanied the frequency changes in weather types. Prior to PH days, areas of greatest height variability were located over the subtropics. Many of these action centers were characterized by heights that have increased and stabilized over time. This suggests that the meridional gradient of atmospheric mass between the subtropics and extratropics may have increased prior to CH days over the Gulf Coast. Composite flow patterns during times of these extremes verified that increased zonal flow may have contributed to the relative paucity of CH events in recent years. Prior to PH days, height variance was concentrated more on the northern fringes of the subtropics than for CH height fields. The presence of a deep trough over eastern North America may not be as important in producing a PH day as in creating a CH day, but the increasing tendency for slight meridional flow over eastern North America may have advected more Pacific anticyclones to the Gulf Coast over time. This degree of amplification may not be sufficient to force continental anticyclones to the region. Collectively, these results verify that changes in continental and Pacific anticyclone frequency are linked to changes in the large-scale flow, and that atmospheric temporal and spatial scale interactions are important in winter. Some significant trends in meteorological variables during CH and PH days were found. Many of these tendencies may be related to large-scale circulation changes on CH and PH days, but others may be produced by changes in the atmosphere in general. No significant trends in the weather type intensities as a whole were identified

Academic Development of First-Year Living-Learning Program Students before and after Hurricanes Katrina and Rita of 2005

Previous research suggests that the far-reaching impacts of hurricanes include the academic performance of students. In an examination of such impacts, we found a trend toward self-perceived decline in some performance indicators relative to students at peer universities. However, few longitudinal impacts were found, perhaps because of the sense of community offered by the living-learning program. These results may inform administrators and faculty of areas for emphasis in mitigating future impacts. Robert V. Rohli is a Professor of Geography and Faculty Director of the Residential Colleges Program at Louisiana State University in Baton Rouge, LA. Kurt J. Keppler is Vice Chancellor for Student Life & Enrollment at Louisiana State University. Daniel L. Winkler is a Graduate Assistant at Louisiana State University

Drivers and impacts of water level fluctuations in the Mississippi River delta: Implications for delta restoration

This review synthesizes the knowledge regarding the environmental forces affecting water level variability in the coastal waters of the Mississippi River delta and relates these fluctuations to planned river diversions. Water level fluctuations vary significantly across temporal and spatial scales, and are subject to influences from river flow, tides, vegetation, atmospheric forcing, climate change, and anthropogenic activities. Human impacts have strongly affected water level variability in the Mississippi River delta and other deltas worldwide. Collectively, the research reviewed in this article is important for enhancing environmental, economic, and social resilience and sustainability by assessing, mitigating, and adapting to geophysical changes that will cascade to societal systems in the coming decades in the economically and environmentally important Mississippi River delta. Specifically, this information provides a context within which to evaluate the impacts of diversions on the hydrology of the Mississippi delta and creates a benchmark for the evaluation of the impact of water level fluctuations on coastal restoration projects worldwide

Spatiotemporal Analysis of the January Northern Hemisphere Circumpolar Vortex Over the Contiguous United States

January 2014 will be remembered for the sensationalized media usage of the term polar vortex which coincided with several polar air outbreaks. A United States polar vortex (USPV) perspective is presented to better understand the January spatial and temporal variability of this regional component of the Northern Hemisphere circumpolar vortex. Use of the monthly mean 5460 m isohypse to represent the location of the USPV extent and area revealed that the spatial features of the January 2014 USPV were not extreme relative to certain 1948–2013 Januaries. Furthermore, the Arctic Oscillation (AO), Pacific-North American (PNA) Pattern, and Pacific Decadal Oscillation (PDO) are all linked to southernmost latitude of the USPV trough, but the PDO and PNA are most closely associated with the longitude at which this latitude occurs. The AO is closely related to the area of the United States enclosed within the USPV

Analytical advances in homeowner flood risk quantification considering insurance, building replacement value, and freeboard

An accurate economic loss assessment for natural hazards is vital for planning, mitigation, and actuarial purposes. The widespread and costly nature of flood hazards, with the economically disadvantaged disproportionately victimized population, makes flood risk assessment particularly important. Here, flood risk is assessed as incurred by the homeowner vs. the flood insurer for insured U.S. properties through the derivation of average annual loss (AAL). AAL is estimated and partitioned using Monte Carlo simulation at the individual home scale, considering insurance coverage and deductible, and the first-floor height (i.e., height of the first floor above the ground), to determine the AAL proportion of homeowners (i.e., apportionment factor) for building and contents, distinguished from that borne by the insurer. In general, AAL estimates suggest that a large portion of the U.S. property flood risk is borne by the flood insurer. The flood insurance policy deductible directly influences the apportionment factor, whereby higher deductibles leave homeowners with a higher annual risk; however, the apportionment factor remains relatively insensitive to coverage values, especially for higher coverage amounts. The homeowner’s flood risk is further reduced by freeboard, with AAL, following an exponential decay trend as freeboard increases. These results reveal new perspectives about how flood insurance protects homeowners from flood risk. In general, the results enhance the proactive decision-making process that allows homeowners to self-assess their degree of preparation and vulnerability to the devastating economic impacts of flood

Improved building-specific flood risk assessment and implications of depth-damage function selection

Average annual loss (AAL) is traditionally used as the basis of assessing flood risk and evaluating risk mitigation measures. This research presents an improved implementation to estimate building-specific AAL, with the flood hazard of a building represented by the Gumbel extreme value distribution. AAL is then calculated by integrating the area under the overall loss-exceedance probability curve using trapezoidal Riemann sums. This implementation is compared with existing AAL estimations from flood risk assessment. A sensitivity analysis is conducted to examine the variability in AAL results based on depth-damage function (DDF) choice. To demonstrate the methodology, a one-story single-family residence is selected to assess the financial benefits of freeboard (i.e., increasing lowest floor elevations). Results show that 1 ft. of freeboard results in annual flood risk reduction of over $1,000, while 4 ft of freeboard results in annual flood risk reduction of nearly$2,000. The sensitivity result suggests that the DDF selection is critical, as a large proportion of flood loss is counted below the top of the first floor. The findings of this paper will enhance DDF selection, improve flood loss estimates, encourage homeowners and communities to invest in flood mitigation, and provide government decision-makers with improved information when considering building code changes

Generalized Cost-Effectiveness of Residential Wind Mitigation Strategies for Wood-Frame, Single Family House in the USA

Wind is one of the deadliest and most expensive hazards in the United States. Wind hazards cause significant damage to buildings and economic losses to homeowners. Economic losses average approximately $3.8 billion annually from hurricane winds and are not decreasing, even despite enhanced construction practices to reduce wind damage. Thus, the effectiveness of mitigation strategies should be evaluated in order to lower the cost incurred by this hazard. Several studies have suggested building code improvements to mitigate the wind hazard, this additional comprehensive research provides selecting economically beneficial mitigation strategies to consider in building code revisions. In a step toward addressing this need, the current study was conducted to determine the cost effectiveness of mitigation strategies for new and retrofit construction of a wood-framed, single-family, residential building case study. Net benefit, defined as the difference between the life-cycle wind loss before and after implementation of the mitigation strategy, was calculated for 15 wind mitigation strategies and their combinations, with new and retrofit construction costs ranging between$1,200 to $12,000 and a decision-making time horizon ranging between 5 and 30 years. Payback periods, defined as the number of years to recover the investment, were calculated for each mitigation strategy. Results were summarized by cost effectiveness for all ASCE 7 wind speed contour intervals. The results of this study serve as a starting point for further refinement of the economic justification needed to properly evaluate potential building code changes

Predictive Statistical Cost Estimation Model for Existing Single Family Home Elevation Projects

One of the most preferred flood mitigation techniques for existing homes is raising the elevation of the lowest floor above the base flood elevation (BFE). Determination of project effectiveness through benefit-cost analysis (BCA) relies on the expected avoided flood loss and the project cost. Conventional construction cost estimates are highly detailed, considering specific details of the project; however, mitigation project decisions must often be made while considering only highly generalized building details. To provide a robust, generalized project cost estimation method, this paper implements data modeling and mining methods such as multiple regression, random forest, generalized additive model (GAM), and model evaluation and selection with cross-validation methods to hindcast elevation costs for existing single-family homes based on average floor area, increase in floor elevation, number of stories, and foundation type. Project cost data for homes elevated in Louisiana, United States, between 2005 and 2015 are used in cost prediction analysis. The statistical modeling results are compared with detailed estimations for several types of home foundations over a range of elevations. The results show substantial agreement between regression predictions and detailed estimates using RSMeans cost data