Late Summer Storms Research Articles

Is the Modern Arctic Marginal Ice Zone More Susceptible to Summer Cyclones?

Abstract As Arctic sea ice melts, cyclones potentially enhance the mechanical and thermodynamic forces that influence the vulnerable ice edge. However, examples can be found in satellite observations and reanalyses where cyclones either locally increase or decrease ice within the marginal ice zone (MIZ). Two case studies with these opposing ice responses are presented. Guided by the tendencies during these events, 264 strong (minimum surface pressure below 984 mb) summer cyclones were sorted by prevailing wind direction and SST changes within the MIZ to quantify the net ice impacts in the present-day Arctic (2010–2019) and early satellite era (1982–1991). By tracking MIZ ice area from one week before the cyclone’s formation through two weeks after, we find cyclones that enhance southerly winds mostly decrease ice area, whereas enhanced northerlies generally increase ice area within the MIZ later in the season. Furthermore, early-summer storms tend to decrease MIZ ice area more than late-summer storms. A shift towards more frequent early-summer storms is observed from the 1980s to 2010s, resulting in almost two-thirds of recent storms decreasing area. Consequently, recent summer cyclones have more negative impacts, resulting in a decline of more than 40,000 km2 of MIZ ice area on average, whereas 1980s cyclones had little aggregate impact. Wind direction and SST trends partially reconcile the wide range of MIZ ice area changes due to cyclone passage, yet considerable variations in individual cyclones’ impacts remain even when controlling for these factors. These bulk diagnostics therefore only explain part of the complex ice-cyclone relationship.

Ecosystem hydrologic and metabolic flashiness are shaped by plant community traits and precipitation

Understanding the hydrologic and carbon cycling consequences of precipitation variability in dryland ecosystems requires improved appreciation and accounting of how above- and belowground biophysical processes differ in their response to rainfall. Our objective was to contrast the sensitivity of dryland ecosystem evapotranspiration (ET), gross ecosystem productivity (GEP), and ecosystem respiration (Re) in response to inter- and intra-annual precipitation variability in a nearby grassland, savanna, and shrubland ecosystems in southeastern Arizona. To do this, we modified the Richards-Baker index, which quantifies the flashiness of a stream’s hydrograph, to calculate analogous indices of ecosystem hydrologic and metabolic flashiness. In this way, ecosystem flashiness describes the frequency and rapidity of short-term fluctuations in H2O and CO2 exchange in response to precipitation while preserving the sequence of day-to-day variation in fluxes using tower-based time-series of daily averaged ET, GEP and Re. We calculated annual hydrologic, GEP, and Re flashiness (fET, fGEP and fRe respectively) using 6 years of daily-averaged fluxes estimated from eddy covariance. In contrast to our prediction, annual fGEP was consistently greater than annual fRe. Furthermore, we predicted that increasing rooting depth would correlate with a decline in annual fET and fGEP. In fact, annual fGEP was similar between the grassland, savanna, and shrubland. Whereas the response of annual fET and fGEP to annual precipitation was plant community dependent and generally declined with increasing rainfall, annual fRe did not vary in response to precipitation. The effect of late summer storms on fGEP was plant community dependent such that shrubland fGEP and fRe strongly declined in response to rainfall whereas grassland and savanna fGEP was relatively unresponsive. Conceptually similar to hydrologic flashiness, ecosystem flashiness may provide an additional lens through which to observe the influence of resource availability, shifts in community composition, and disturbance on ecosystem hydrologic and carbon cycling.

Puerto Rico sea level trend in regional context

Sea level (SL) is rising in Puerto Rico due to regional influences from weaker trade winds, in addition to global influences of thermal expansion and polar ice melt. The linear increase of SL has steepened in recent decades from +0.175 to +0.725 cm/yr. The faster rate of SL rise is partly attributed to diminishing ice volume (r = −0.80), notwithstanding a recent decline in the Atlantic Multi-decadal Oscillation. A sophisticated point-to-field regression analysis (N = 5980) demonstrates that daily fluctuations of SL in Puerto Rico are significantly enhanced by locally warmer sea temperatures via reduced evaporation, and correspond with lower air pressure accompanying late summer storms. These features point to regional air-sea interactions that affect SL rise over and above the background global signal. Extrapolating these trends, a rise of more than 0.3 m is expected by 2050.

Wood density of silver fir reflects drought and cold stress across climatic and biogeographic gradients

Climate influences wood density and this relationship affects the ability of conifer forests to uptake and store carbon. Some conifer species can show mixed responses to long-term climate variability in their within-ring width and density patterns. Here we analyze if tree-ring width and density differently respond to seasonal climate variability in silver fir (Abies alba) forests from the Spanish Pyrenees subjected to cold and Mediterranean influences. In these forests, early growing-season dry conditions increase minimum wood density, possibly by reducing lumen diameter and lowering growth rates. Cold conditions during the late growing season are associated to a decrease in maximum wood density, probably through a reduction in the lignification and thickening rates of latewood tracheids. We test if these associations follow climatic and biogeographic patterns since the Mediterranean influence, characterized by late-summer storms which alleviate drought stress, is prevalent eastwards in this region. Silver-fir intra-annual width and wood density data showed mixed responses to climate. Minimum wood density negatively responded to spring precipitation, particularly in dry sites forming the southernmost distribution limit of the species. Maximum wood density positively responded to mean maximum temperatures and sunshine duration during late summer and early autumn, mainly in eastern sites subjected to a dominant Mediterranean influence where late-summer drought stress is expected to be low. More extreme climate conditions including dry spells could shift minimum wood density and reduce hydraulic conductivity and growth in conifer species as silver fir which dominate mesic sites. Warmer conditions would lead to denser latewood in silver fir if accompanied by longer durations of sunshine.

Observations of two nuisance stalk-forming diatoms (Bacillariophyta) from a river in Connecticut, Northeastern U.S.A.: Didymosphenia sp. and Cymbella janischii (A. Schmidt) De Toni

The nuisance taxon Didymosphenia geminata was reported in the West Branch of the Farmington River in March, 2011 after a fisherman detected cotton-like tufts attached to rocks. In response, the Connecticut Department of Energy and Environmental Protection (CT DEEP) conducted a comprehensive survey of the river system. After major late summer storms, Didymosphenia geminata was not observed again. Surveys in 2012–2013 tracked the spatial and temporal distribution of stalk-forming diatoms at the confluence of the West Branch of the Farmington and Still Rivers, thereby allowing comparison of data from adjacent rivers with distinct water chemistries. Water chemistry and temperature data were collected to characterize nutrient concentrations associated with these diatoms. Surveys showed no evidence of Didymosphenia geminata but four native stalk-forming diatom species and a taxon previously unreported in Connecticut, Cymbella janischii, were observed throughout the year. Also from November, 2012 through June, 2013, a morphologically distinct diatom in the genus Didymosphenia was observed growing prolifically bank to bank with thick mats of long filamentous stalks. Subsequent examination revealed that the taxon previously reported as Didymosphenia geminata was instead a different taxon, Didymosphenia sp. Furthermore, Didymosphenia sp. continued to flourish in the West Branch of the Farmington River, absent from the neighbouring Still River, suggesting that the physiochemical features and in particular higher nutrients may limit the distribution of this diatom. In contrast, C. janischii was found growing abundantly further downstream in warmer water and higher nutrient levels.

Río Tinto sedimentary mineral assemblages: A terrestrial perspective that suggests some formation pathways of phyllosilicates on Mars

The presence of extensive phyllosilicate deposits from the early Noachian of Mars are often interpreted as having formed from neutral to subalkaline solutions. In this paper we examine the Río Tinto fluvial basin, an early Mars analog, that hosts clay production and sedimentation along the entire course of the river. At Río Tinto, phyllosilicate minerals including clays and micas are sourced by volcanosedimentary bedrock of rhyolitic and andesitic composition affected by Carboniferous hydrothermal alteration. Pleistocene to modern acidic weathering of those materials chemically altered the volcanic and sedimentary materials to K/Na–clay–(montmorillonite/smectites)–kaolinite assemblages in paleosoils and fractures while physical weathering degrades phyllosilicates more resistant to acidic attack. During the wet season, phyllosilicates are eroded, transported and deposited from both acidic headwaters and neutral tributaries. During the dry season, sulfates and nanophase oxyhydroxides co-precipitate. Late summer storms that cause fast flooding events mix illite, quartz, feldspars, iron oxides and other minerals in fluvial deposits where these minerals are stabilized and aggrade until the following wet season. As a result, chemical precipitates, primary phyllosilicates and secondary clays form mineral admixtures that explain the compositional diversity of the fluvial deposits. These deposits reveal the persistence of smectites, whose occurrence is explained given that the reaction kinetics under acidic conditions of degradation is lowered by seasonal discharges of the river. The longevity of phyllosilicate minerals within fluvial deposits depends on climatic and geochemical conditions and processes which are in turn are correlated to temperature, persistence of water, hydrological cycling, hydrogeochemistry and composition of the source materials in the basement. These parameters are universal and have to be characterized in order to understand the distribution of mineral composition on any planetary surface, including Mars.

INFLUENCE OF SUMMER MANAGEMENT PRACTICES OF GRAZED WHEAT PASTURES ON RUNOFF, SEDIMENT, AND NUTRIENT LOSSES

The agricultural economy of the southern Great Plains relies on practices that incorporate grazed winter wheatand associated summer management practices. Information exists about the impact of these practices on water quality, butdata related to runoff and associated nutrient and sediment movement due to high intensity, late summer storms in the southernGreat Plains are limited. This study examined runoff and runoff water quality from two winter wheat management strategies:winter wheat with summer chemical fallow (WWF) and winter wheat with summer legumes (WWSL) and two grazingtreatments (grazed and ungrazed) from 1998 to 2002. Four pastures were planted in conservation winter wheat and grazedfrom November to May. Summer legumes were direct seeded in two of the pastures in March and grazed mid-July to September.Runoff from plots (1.5 3 m) was quantified with a rainfall simulator, with rainfall intensities representing a late summer,short duration (15 min), high intensity (10 cm/h) summer storm. Runoff samples were analyzed for nitrate-N (NO3-N),bioavailable and water-soluble phosphorus (BAP and WSP, respectively), and sediment yield. Overall, the WWF practice hadgreater runoff, sediment, and nutrient losses than the WWSL strategy. Likewise, grazing produced greater runoff, sediment,and nutrient losses than ungrazed plots. The worst-case scenario was WWF pastures that incorporated winter grazing, with71% of applied rainfall lost as runoff. The greatest losses for sediment (284 kg/ha), NO3-N (124 kg/ha), BAP (380 g/ha), andWSP (38 g/ha) were found with the grazed WWF practice. Understanding the mechanism of interaction between late summerstorms and summer management practices will improve large-scale mitigation strategies to reduce erosion and enhancecapture of water resources.

Monitoring the perennial martian northern polar cap with MGS MOC

We have used the Mars Global Surveyor Mars Orbiter Camera Wide Angle (MGS MOC WA) dataset to study albedo trends on the martian northern residual cap. Six study regions were selected, the Chasma Boreale source region, three regions near the center of the cap (“fish hook” region, latitude = 87°; “bottle opener” region, latitude = 87°, “steep-shallow” region, latitude = 85°), and two lower latitude regions (crater, latitude = 77°, and polar outlier, latitude = 82°), and the albedos of these six regions were examined. These regions were chosen due to their good temporal coverage in the MOC dataset, as well as having been studied by other researchers (Bass et al., 2000, Icarus 144, 382–396; Calvin and Titus, 2004, Lunar Planet. Sci. XXXV, Abstract 1455). The picture which emerges is complex. Most areas experience a combination of darkening and brightening through the northern summer; only one area consistently brightens (the polar outlier region). A good deal of interannual repeatability in each region's albedo behavior is seen, however. Possible causes for the observed complex behaviors include dust deposition from late summer storms, sintering of frost grains over the course of the summer, and cold trapping of volatiles on bright, cold surfaces.

Atmosphere–Ocean Coupled Dynamics of Cyclones in the Midlatitudes

Abstract It is well known that hurricane intensity is influenced by factors such as the storm's initial intensity, the spatial extent of the storm, the thermodynamic state of the atmosphere through which it moves, the storm propagation speed, and sea surface fluxes along the storm track. Although several of these factors are also known to modulate the strength of midlatitude cyclone systems, little is known about the impact of air–sea interactions on storms outside the Tropics. To investigate the atmosphere–ocean dynamics of midlatitude North Atlantic storms, the Canadian Mesoscale Compressible Community (MC2) atmospheric model is coupled to the Princeton Ocean Model. Case studies include midlatitude extratropical storm Earl (1998) and an intense winter storm from January 2000, hereafter denoted Superbomb. On one hand, late-summer storms such as Earl encounter a thin mixed layer and produce a cold wake by inducing strong currents. Sea surface temperatures (SSTs) can be depressed as much as 5°C or more. On...

Chemical interactions and sediments of the western Canadian arctic shelf

The Canadian Beaufort Shelf is the largest continental shelf on the North American side of the Arctic and is the most brackish of all Arctic shelves. Chemical data both site-specific and from the Arctic Ocean interior are reviewed for evidence of chemical processes which occur at the shelf-seabed/water interface. The important material sources to this region include the Mackenzie River, shore erosion, primary production, and long-range atmospheric transport. The latter source appears to be important for chlorinated organics. For the past two decades hydrocarbon exploration has had a local impact around drill-sites where cuttings and drill muds have been discharged. The chemical environment of the Canadian Beaufort Shelf nearshore is exceedingly dynamic due to processes mediated by ice (scour, brine drainage, water disposition) and winds (sediment resuspension and upwelling). Storms from the northwest in late summer, when there is open water, have the potential to resuspend bottom sediments in the nearshore (less than about 20 m water depth) bringing about the transport of detritus and remineralized material. Future research on seabed chemical interactions should focus on the measurement of seasonal fluxes of materials to and from the seabed, the sources of carbon to the shelf, denitrification in sediments, the response of the nearshore to late summer storms and the role of Arctic shelf sediments to the budget of chlorinated organic contaminants.

Influence of Lake Surface Area and Depth Upon Thermal Stratification and the Depth of the Summer Thermocline

Among the important physical characteristics of a lake are whether it stratifies seasonally, and if so, the depth to which wind-mixing is limited by the stratification. It is generally known that sufficiently shallow lakes tend to remain isothermal throughout the year and that the depth of the thermocline in stratified lakes correlates positively with the surface area of the lake. Observations from lakes in several different regions of the temperate zone of the northern hemisphere show that whether a lake stratifies depends on both the maximum depth and the surface area of the lake, whereas the depth of the thermocline depends primarily on the surface area. A modification of previously published scaling arguments provides a plausible theoretical basis for some of this behavior. These arguments account for additional shear-induced mixing associated with the fundamental internal seiche in small lakes and with near-inertial motion in big lakes. For lakes of cross-basin diameter less than 5,000 m (surface area less than 25 km 2), an estimate of the depth of the thermocline, h, at the time of maximum heat content is given by: h ≅ 2.0 ( τ g Δ ρ ) 1 / 2 L 1 / 2 where τ is the wind stress associated with late summer storms, Δp is the density contrast between epilimnion and hypolimnion typical for lakes in that region near the time of maximum heat content, g is the gravitational acceleration, and L is the square root of the surface area of the lake. A consistent set of units must be employed.