Increased Storm Intensity Research Articles

Ecohydrology of a semi‐arid forest: partitioning among water balance components and its implications for predicted precipitation changes

AbstractThe distribution of precipitation inputs into different hydrological components of water‐limited forest ecosystems determines water availability to trees and consequently forest productivity. We constructed a complete hydrological budget of a semi‐arid pine forest (285 mm annual precipitation) by directly measuring its main components: precipitation (P), soil water content, evapotranspiration (ET, eddy covariance), tree transpiration (sap flux), soil evaporation (soil chambers), and intercepted precipitation (calculated). Our results indicated that on average for the 4‐year study period,ETaccounted for 94% ofP, varying between 100% whenP< 250 mm and 85% whenP> 300 mm (with indications for losses to subsurface flow and soil moisture storage in wetter years). Direct measurements of the components of theETflux demonstrated that both transpiration and soil evaporation were significant in this dry forest (45% and 36% ofET, respectively). Comparison between ecosystemET(eddy covariance measurements) and the sum of its measured components showed good agreement on annual scales, but up to 30% discrepancies (in both directions) on shorter timescales. The pulsed storm pattern, characteristics of semi‐arid climates, was sufficient to maintain the topsoil layer wet during the whole wet season. Only less often and intensive storms resulted in infiltration to the root zone, increasing water availability for uptake by deeper roots. Our results indicate that climate change predictions that link reduced precipitation with increased storm intensity may have a smaller effect on water availability to forest ecosystems than reduced precipitation alone, which could help forests' survival and maintain productivity even under drier conditions. Copyright © 2009 John Wiley & Sons, Ltd.

Environmental Ingredients for Supercells and Tornadoes within Hurricane Ivan

Abstract Hurricane Ivan (2004) was a prolific producer of tornadoes as it made landfall on the U.S. Gulf Coast. Prior researchers have revealed that the tornadic cells within tropical cyclone (TC) rainbands are often supercellular in character. The present study investigates the utility of several common midlatitude, continental supercell and tornado diagnostic tools when applied to Hurricane Ivan’s tornado episode. The environment within Hurricane Ivan was favorable for storm rotation. While well offshore, the bands of Hurricane Ivan possessed embedded cells with mesocyclones of moderate intensity. A dual-Doppler analysis reveals that the updrafts of these cells were highly helical in the lower troposphere, suggesting significant ingestion of streamwise environmental vorticity. These coherent cells were long lived and could be tracked for multiple hours. As the supercells over the Gulf of Mexico approached the coast during Ivan’s landfall, rapid increases in midlevel vorticity and vertically integrated liquid (VIL) occurred. Based on compiled severe weather reports, these increases in storm intensity appear often to have immediately preceded tornadogenesis. The local environment for supercells in Ivan’s interior is evaluated through the use of 62 soundings from the operational land-based network and from research flights. There were substantial differences in the thermodynamic profiles and wind profiles at differing ranges from Ivan’s center, from quadrant to quadrant of Ivan’s circulation, and between land and sea. The most optimal environment for supercells and tornadoes occurred in the most interior section of Ivan’s right-front quadrant, with conditions being even more favorable over land than over the sea. For contrast, comparable values are presented for Hurricane Jeanne (2004), which was similar to Ivan in several respects, but was not a prolific tornado producer at landfall. Although both storms provided environments with comparable shallow—and deep—layer vertical wind shear, the Ivan environment had notably more CAPE, likely due to a prominent dry air intrusion. This increase in CAPE was reflected in substantial increases in common operational forecasting composite indices. The results suggest that the conventionally assessed ingredients for midlatitude continental supercells and tornadoes can be readily applied to discriminate among TC tornado episodes.

Multi‐indices analysis of southern Scandinavian storminess 1780–2005 and links to interdecadal variations in the NW Europe–North Sea region

AbstractExtra‐tropical cyclone frequency and intensity are currently under intense scrutiny because of the destruction recent windstorms have brought to Europe, and because they are a major meridional heat transport mechanism that may respond to differential latitudinal warming trends. Several studies using reanalysis data covering the second half of the 20th century suggest increasing storm intensity in the northeastern Atlantic and European sector. Fewer analyses cover a longer time period but show different trends or point towards the dominance of interdecadal variability instead of any clear trends. Hence, it is relevant to analyse cyclone variability over as long a period as possible. In this study, we analyse interdecadal variability in cyclone activity over northwestern Europe back to AD 1780 by combining information from eight storminess indices applied in an Eulerian framework. These indices, including four new approaches towards gauging cyclone activity, use the series of thrice‐daily sea level pressure observations at Lund and Stockholm. We find pronounced interdecadal variability in cyclonic activity but no significant overall consistent long‐term trend. The major interdecadal‐scale variability common to all indices is in good agreement with geostrophic wind reconstructions for NE Atlantic and NW Europe, and with variations in the North Atlantic oscillation (NAO). Our results show that the reanalysis studies cover a time period chiefly coinciding with a marked, but not exceptional in our 225‐year perspective, positive variation in the regional cyclone activity that has more recently reversed. Because of the interdecadal variations, a near‐centennial time perspective is needed when analysing variations in extra‐tropical cyclone activity and the associated weather conditions over northwestern Europe. Copyright © 2009 Royal Meteorological Society

Characteristics of low‐latitude Pc1 pulsations during geomagnetic storms

We use search‐coil magnetometer data from a low‐latitude station in Parkfield, California (L = 1.77) to study the occurrence of Pc1 pulsations associated with geomagnetic storms. The Pc1 pulsations and storms are identified using automatic algorithms, and the statistical distributions are examined using a superposed epoch analysis technique, as a function of local time, time relative to storm main phase, and storm intensity. Results show that Pc1 pulsations are 2–3 times more likely (than normal) to be observed in the 2–4 d following moderate storms and 4–5 times more likely in the 2–7 d following intense storms. The Pc1 frequencies are higher in moderate storms than they are in nonstorm times and become even higher and occupy a greater range of local times as the strength of the storms increase. These results are consistent with the idea that the source of EMIC waves extends to lower L values as storm intensity increases.

Danish Attitudes and Reactions to the Threat of Sea-Level Rise

Abstract The Danish coastline has continually changed since the last ice age with relative subsidence in the south and uplift in the north. The result is a low-lying country with raised beaches and wide marine forelands in the north and an archipelago in the south. The coastline is relatively long (7400 km) for an area of 42,000 km2. Eighty percent of the population of 5.33 million (1 January 2000) live in municipalities with a coastline. Vulnerable low-lying areas contain 60,000 to 70,000 properties. These areas are mainly raised sea floor, marshes, and reclaimed areas. On the basis of present vertical movements and projected global accelerated sea-level rise (ASLR) it is estimated that relative sea level will increase by 33–46 cm within the next 100 years—notably in the southwestern part of Denmark. Increased storm intensity may enhance the impacts of this change in water level. Dikes protect about 1100 km of the coastline and hard structures about 700 km. Soft solutions, especially beach nourishment, a...

Climate feedback implied by observed radiation and precipitation changes with midlatitude storm strength and frequency

Current climate observations are used to quantify the relationships between midlatitude storm strength and frequency and radiation and precipitation properties. Then, the derived radiation/precipitation‐storm relationships along with the midlatitude storm changes with climate‐warming predicted by a climate model are used to determine the radiation and precipitation changes resulting from an increase in midlatitude storm intensity and a decrease in midlatitude storm frequency. Increases in midlatitude storm intensity produce shortwave cooling and longwave warming while decreases in storm frequency produce the opposite effects. When the two changes are added together the increase in storm strength dominates producing a shortwave cooling effect of 0–3.5 W/m2 and a longwave warming effect of 0.1–2.2 W/m2. For precipitation, the increase in storm intensity also dominates the decrease in storm frequency and produces an increase in precipitation of 0.05–0.08 mm/day.

Storms and shoreline retreat in the southern Gulf of St. Lawrence

Storms play a major role in shoreline recession on transgressive coasts. In the southern Gulf of St. Lawrence (GSL), southeastern Canada, long-term relative sea-level rise off the North Shore of Prince Edward Island has averaged 0.3 m/century over the past 6000 years (>0.2 m/century over 2000 years). This has driven long-term coastal retreat at mean rates >0.5 m/a but the variance and details of coastal profile response remain poorly understood. Despite extensive sandy shores, sediment supply is limited and sand is transferred landward into multidecadal to century-scale storage in coastal dunes, barrier washover deposits, and flood-tidal delta sinks. Charlottetown tide-gauge records show mean relative sea-level rise of 3.2 mm/a (0.32 m/century) since 1911. A further rise of 0.7±0.4 m is projected over the next 100 years. When differenced from tidal predictions, the water-level data provide a 90-year record of storm-surge occurrence. Combined with wind, wave hindcast, and sea-ice data, this provides a catalogue of potentially significant coastal storms. We also document coastal impacts from three recent storms of great severity in January and October 2000 and November 2001. Digital photogrammetry (1935–1990) and shore-zone surveys (1989–2001) show large spatial and temporal variance in coastal recession rates, weakly correlated with the storm record, in part because of wave suppression or coastal protection by sea ice. Large storms cause rapid erosion from which recovery depends in part on local sand supply, but barrier volume may be conserved by washover deposition. Barrier shores with dunes show high longshore and interdecadal variance, with extensive multidecadal healing of former inlet and overwash gaps. This reflects recovery from an episode of widespread overwash prior to 1935, possibly initiated by intense storms or groups of storms in the latter half of the 19th century. With evidence from the storms of 2000–2001, this points to the importance of storm clustering on scales of weeks to years in determining erosion vulnerability, as well as the need for a long-term, large-scale perspective in assessing coastal stability. The expected acceleration in relative sea-level rise, together with projections of increasing storm intensity and greatly diminished winter ice cover in the southern GSL, implies a significant increase in coastal erosion hazards in future.

Precipitation Distribution in Tropical Cyclones Using the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager: A Global Perspective

TRMM microwave imager rain estimates are used to quantify the spatial distribution of rainfall in tropical cyclones (TCs) over the global oceans. A total of 260 TCs were observed worldwide from 1 January 1998–31 December 2000, providing 2121 instantaneous TC precipitation observations. To examine the relationship between the storm intensity, its geographical location, and the rainfall distribution, the dataset is stratified into three intensity groups and six oceanic basins. The three intensity classes used in this study are tropical storms (TSs) with winds <33 m s−1, category 1–2 hurricane-strength systems (CAT12) with winds from 34–48 m s−1, and category 3–5 systems (CAT35) with winds >49 m s−1. The axisymmetric component of the TC rainfall is represented by the radial distribution of the azimuthal mean rainfall rates (R). The mean rainfall distribution is computed using 10-km annuli from the storm center to a 500-km radius. The azimuthal mean rain rates vary with storm intensity and from basin to basin. The maximum R is about 12 mm h−1 for CAT35, but decreases to 7 mm h−1 for CAT12, and to 3 mm h−1 for TS. The radius from the storm center of the maximum rainfall decreases with increasing storm intensity, from 50 km for TS to 35 km for CAT35 systems. The asymmetric component is determined by the first-order Fourier decomposition in a coordinate system relative to the storm motion. The asymmetry in TC rainfall varies significantly with both storm intensity and geographic locations. For the global average of all TCs, the maximum rainfall is located in the front quadrants. The location of the maximum rainfall shifts from the front-left quadrant for TS to the front-right for CAT35. The amplitude of the asymmetry varies with intensity as well; TS shows a larger asymmetry than CAT12 and CAT35. These global TC rainfall distributions and variability observed in various ocean basins should help to improve TC rainfall forecasting worldwide.

Altered Rainfall Patterns, Gas Exchange, and Growth in Grasses and Forbs

Although the potential for increased temperature is the primary and best‐studied aspect of anthropogenic climate change, altered rainfall patterns, increased storm intensity, and more severe droughts are also predicted in most climate‐change scenarios. We altered experimentally the rainfall regime in a native tallgrass prairie in northeastern Kansas and assessed leaf‐level physiological activity and plant growth responses for C3 and C4 plant species. Our primary objective was to contrast the importance of reductions in rainfall quantity (30% smaller rain events, no change in rainfall pattern) with an altered, more extreme distribution of rainfall (no reduction in total growing‐season quantity, 50% increased inter‐rainfall dry intervals) for these dominant species from the two main plant functional groups (C4 grasses, C3 forbs) present in many grasslands. Leaf water potential (ψl), net photosynthetic carbon gain ($$A_{\mathrm{CO}\,_{2}}$$ ), specific leaf mass, leaf C:N ratio, growth rate for Andropogon gerardii (C4 grass) and Solidago canadensis (C3 forb), vegetative and flowering stem densities, and canopy light penetration for grass and forb assemblages were intensively monitored during the 1999 growing season in a long‐term rainfall manipulation study at the Konza Prairie Biological Station. Soil water content at 0–30 cm depth was more variable in response to the altered rainfall distribution compared to the reduced‐quantity treatment. In S. canadensis, $$A_{\mathrm{CO}\,_{2}}$$ , gs (stomatal conductance), A:Ci (leaf stomatal [CO2]), and A:E (estimated leaf transpiration rate) were positively correlated with soil water content, but no relationship was seen for A. gerardii, indicating that even though this dominant grass species has most of its roots in the upper 30 cm of the soil, A. gerardii was buffered physiologically from increased resource variability. There were few significant responses in growth parameters in either grasses or forbs, but canopy light penetration increased with both rainfall treatments. We concluded (1) that the temporal variability in rainfall inputs can have as much impact on soil moisture as simple reductions in rainfall quantities with no change in temporal distribution, (2) that responses of A. gerardii and S. canadensis to altered rainfall distributions were not consistent with common views of soil resource partitioning between shallow‐rooted grasses and deep‐rooted forbs, and (3) that altered rainfall patterns may have the potential to offset elevated CO2 impacts on grassland vegetation.

Temporal variation in the wavelength of hummocky cross-stratification: Implications for storm intensity through Mesozoic and Cenozoic

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Simulated interior floods and the flood experience in urban communities

The Hydrologie Engineering Center (HEC-1) model was used to construct synthetic hydrographs for isolated interior urban floods. Flood peak and lag time were very well preserved in simulated flows. Total volume was not adequately expressed. Lag time varied inversely with both urban development and storm intensity. Peak discharge varied with storm intensity, but this variability was well defined only at very high urbanization levels. An 175% increase in storm intensity produced a change of about 15% in peak discharge. Claims for flood damage correlated well with estimates of peak flow and lag time combined. Other measures of flood experience also correlated with the two features. Within the range of storms utilized, urban development factors consistently outranked storm intensity as a determining factor in flood damage.

Growth rate and decay of magnetospheric ring current

The rate of energy input to the ring current is studied as a function of solar wind parameters. The ring current dissipation rate is also examined. The decay constant τ in the main phase of a storm has been shown to be independent of its intensity and to equal (4 ± 2) h. In the recovery phase τ rises with increasing storm intensity.

Hurricane tritium II: Air-sea exchange of water in Betsy 1965

The radial and vertical distribution of tritium (as HTO) in rain water and in water vapor was investigated in hurricane Betsy on four days, each day having different storm characteristics. On one day, 3 September, stratospheric subsidence was detected in the eye. The tritium concentration of underlying seawater was also measured. The molecular exchange of water at the air/sea interface was clearly exhibited on all four days, and the extent of exchange increased with increasing storm intensity. On 3 September the wall cloud vapor had a composition equivalent to 86% seawater vapor and 14% vapor from outside the storm envelope. Together with the measured radial distribution of total wind velocity and reasonable assumptions of the effect of spray on rate of exchange, the tritium data were used to calculate possible distributions of relative inflow angle and of specific vapor inflow. A maximum in the inflow function around 120 km was obtained in one case, indicating subsidence between 200 km and 120 km. In the same area the distribution of tritium changes drastically from a vertical gradient to vertically well mixed and a horizontal gradient. DOI: 10.1111/j.2153-3490.1968.tb00401.x

Hurricane tritium II: Air-sea exchange of water in Betsy 1965

The radial and vertical distribution of tritium (as HTO) in rain water and in water vapor was investigated in hurricane Betsy on four days, each day having different storm characteristics. On one day, 3 September, stratospheric subsidence was detected in the eye. The tritium concentration of underlying seawater was also measured. The molecular exchange of water at the air/sea interface was clearly exhibited on all four days, and the extent of exchange increased with increasing storm intensity. On 3 September the wall cloud vapor had a composition equivalent to 86% seawater vapor and 14% vapor from outside the storm envelope. Together with the measured radial distribution of total wind velocity and reasonable assumptions of the effect of spray on rate of exchange, the tritium data were used to calculate possible distributions of relative inflow angle and of specific vapor inflow. A maximum in the inflow function around 120 km was obtained in one case, indicating subsidence between 200 km and 120 km. In the same area the distribution of tritium changes drastically from a vertical gradient to vertically well mixed and a horizontal gradient. DOI: 10.1111/j.2153-3490.1968.tb00401.x

Some Aspects of Hawaiian Rainfall *

The question is raised whether rainfall over the sugar and pineapple plantations in the central parts of the island of Oahu in the Hawaiian group is so sporadic and disorganized that it is not amenable to short term forecasting, or whether it occurs in sufficiently organized form so that general synoptic forecasts for Hawaii can be supplied that will be useful for operations on the plantations. It turns out that most rainfall is attributable to synoptic disturbances. This is more true in winter, when the islands normally experience their heaviest rainfall, than in summer, when precipitation is at its seasonal low ebb. Further analysis of the disturbances shows that a few large storms produce over ⅔ of the annual rainfall total and that the orographic effect responsible for local differences in rainfall received from storms decreases in importance as storm intensity increases.