Characterizing the Northern Hemisphere Circumpolar Vortex Through Space and Time

This hemispheric-scale, steering atmospheric circulation represented by the circumpolar vortices (CPVs) are the middle- and upper-tropospheric wind belts circumnavigating the poles. Variability in the CPV area, shape, and position are important topics in geoenvironmental sciences because of the many links to environmental features. However, a means of characterizing the CPV has remained elusive. The goal of this research is to (i) identify the Northern Hemisphere CPV (NHCPV) and its morphometric characteristics, (ii) understand the daily characteristics of NHCPV area and circularity over time, (iii) identify and analyze spatiotemporal variability in the NHCPV’s centroid, and (iv) analyze how CPV features relate to the air-sea teleconnections that are known to explain important variability in weather/climate. Daily data (1979─2017) were collected from the National Centers for Environmental Prediction at the 500-hPa geopotential height level, and processed and analyzed in Python, MATLAB, R, and ArcGIS Desktop platform. Results suggest that the innovative method improves the calculation of NHCPV area and circularity, proven with the significant correlations between the NHCPV and teleconnection indices. At a daily scale, both correlations and principal components analysis reveal that the NHCPV is closely related to some air-sea teleconnections. The NHCPV area has expanded linearly over the 1979─2017 period and within its four subperiods, likely because of the weakened gradient of atmospheric mass over time. On the other hand, the NHCPV has alternating periods of increasing and decreasing circularity, suggesting that it may have become more unstable in its delivery of west-to-east flow. Spectrum analysis shows distinct annual and semiannual cycles for the area and circularity over all periods. While the NHCPV centroid shifts annually and intra- annually throughout the time series, probably because of the seasonality and teleconnection linkage, the linear trend analysis shows that the day-to-day distance moved by the NHCPV centroid decreased significantly, suggesting stability in the centroid positions. Emerging hot spot analysis reveals that new and oscillating hot spots have been emerged over time. This research can be extended to understand the current and projected relationship between the full 4-D (x-y-z-t) feature-based CPV structure, ocean-air teleconnections, sea-ice forcing, and natural hazard impacts

Modeling Tropical Cyclone Storm Surge and Wind Induced Risk along the Bay of Bengal Coastline Using a Statistical Copula

High winds, torrential rain, and storm surges from tropical cyclones cause massive destruction to property and cost the lives of many people. Among the coastal areas affected by these major natural calamities, the coastline of the Bay of Bengal (BoB) ranks as one of the most susceptible to tropical cyclone storm surge risk due to its geographical setting and population density, Bangladesh suffers the most. The purpose of this study is to describe the relationship between storm surge at the BoB and peak reported wind and describe the dependency structure between wind speeds and storm surges at that location. Various models have been developed to predict storm surge in this region but none of them quantify statistical risk with empirical data. This research demonstrates a methodology for estimating the return period of the joint hazard based on a bivariate copula model. An Archimedean Gumbel copula with Weibull and normal margins is specified for the result the coast of BoB can expect a cyclone with peak reported winds of at least 24 m s−1 and surge heights of at least 4.0 m, on average, once every 3.2 years (2.7–3.8). The BoB can expect peak reported winds of 62 m s−1 and surge heights of at least 8.0 m, on average, once every 115.4 years (55.8–381.1). In this ocean basin, surge heights are comparably higher when compared to other ocean basins. Application of the copula will mitigate future threats of storm surge impacts on coastal communities of the BoB

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

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

Historical global and regional spatiotemporal patterns in daily temperature

The abrupt increase in surface air temperature over the last few decades has received abundant scholarly and popular attention. However, less attention has focused on the specific nature of the warming spatially and seasonally, using high-resolution reanalysis output based on historical temperature observations. This research uses the European Centre for Medium-range Weather Forecasts (ECMWF) Reanalysis Version 5 (ERA5) output to identify spatiotemporal features of daily mean surface air temperature, defined both as the mean of the maximum and minimum temperatures over the calendar day (“meanmaxmin”) and as the mean of the 24 hourly observations per day (“meanhourly”), across the terrestrial Earth. Results suggest temporal warming throughout the year, with several “hot spots” of significantly increasing temperature, including in the Arctic transition seasons, Northern Hemisphere mid-latitudes in July, Eurasia in spring, Europe and the lower latitudes in summer, and tropical autumn. Cooling is also observed, but generally at rates more likely to be statistically insignificant than warming rates. These trends are nearly identical regardless of whether calculated as “meanmaxmin” or “meanhourly.” These results may assist scientists and citizens to understand more fully observed agricultural, commercial, ecological, economic, and recreational trends in light of climate change considerations

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

Estimating Future Residential Property Risk Associated with Wildfires in Louisiana, U.S.A.

Wildfire is an important but understudied natural hazard in some areas. This research examined historical and future wildfire property risk at the census-block level in Louisiana, a U.S.A. state with relatively dense population and substantial vulnerability to loss from wildfire, despite its wet climate. Here wildfire risk is defined as the product of exposure and vulnerability to the hazard, where exposure is a function of the historical and anticipated future wildfire frequency/extent, and vulnerability is a function of population, structure and content property value, damage probability, and percent of properties damaged. The results revealed a historical (1992–2015) average annual statewide property loss due to wildfire of almost USD 5.6 million (in 2010 USD), with the greatest risk in southwestern inland, east-central, extreme northwestern, and coastal southwestern Louisiana. The geographic distribution of wildfire risk by 2050 will remain similar to that today, but the magnitude of losses was projected to increase statewide to over USD 11 million by 2050 (in 2010 USD), an increase of more than 100% over 2010 values. These estimates are conservative, as they did not include crop, forestry, or indirect losses (e.g., cost of evacuation and missed time at work). Overall, results suggested that increased efforts are needed to contain wildfires, to reduce the future risk of this increasing and underestimated hazard