Geology topics

D. Reynolds

Publications and source records attributed to D. Reynolds.

4 recordsLinked to original sources

USGS2016

Data, age uncertainties and ocean δ 18 O under the spotlight for Ocean2k Phase 2

The oceans make up 71% of the Earth’s surface area and are a major component of the global climate system. They are the world’s primary heat reservoir, and knowledge of the global ocean response to past and present radiative forcing is important for understanding climate change. PAGES’ Ocean2k working group aims to place marine climate of the past century within the context of the previous 2000 years (2k). Phase 1 (2011-2015) focused on constraining the forcing mechanisms most consistent with reconstructed sea surface temperature (SST) over the 2k interval (McGregor et al. 2015; Tierney et al. 2015). The 1st Ocean2k workshop assisted in the transition to Ocean2k Phase 2 (2015-2017), with the workshop goal to develop, coordinate and significantly advance community-identified and -driven activities.

Past Global Changes↗

USGS2011

Design and quantification of an extreme winter storm scenario for emergency preparedness and planning exercises in California

The USGS Multihazards Project is working with numerous agencies to evaluate and plan for hazards and damages that could be caused by extreme winter storms impacting California. Atmospheric and hydrological aspects of a hypothetical storm scenario have been quantified as a basis for estimation of human, infrastructure, economic, and environmental impacts for emergency-preparedness and flood-planning exercises. In order to ensure scientific defensibility and necessary levels of detail in the scenario description, selected historical storm episodes were concatentated to describe a rapid arrival of several major storms over the state, yielding precipitation totals and runoff rates beyond those occurring during the individual historical storms. This concatenation allowed the scenario designers to avoid arbitrary scalings and is based on historical occasions from the 19th and 20th Centuries when storms have stalled over the state and when extreme storms have arrived in rapid succession. Dynamically consistent, hourly precipitation, temperatures, barometric pressures (for consideration of storm surges and coastal erosion), and winds over California were developed for the so-called ARkStorm scenario by downscaling the concatenated global records of the historical storm sequences onto 6- and 2-km grids using a regional weather model of January 1969 and February 1986 storm conditions. The weather model outputs were then used to force a hydrologic model to simulate ARkStorm runoff, to better understand resulting flooding risks. Methods used to build this scenario can be applied to other emergency, nonemergency and non-California applications.

California↗

USGS2010

Assessment of extreme quantitative precipitation forecasts and development of regional extreme event thresholds using data from HMT-2006 and COOP observers

Extreme precipitation events, and the quantitative precipitation forecasts (QPFs) associated with them, are examined. The study uses data from the Hydrometeorology Testbed (HMT), which conducted its first field study in California during the 2005/06 cool season. National Weather Service River Forecast Center (NWS RFC) gridded QPFs for 24-h periods at 24-h (day 1), 48-h (day 2), and 72-h (day 3) forecast lead times plus 24-h quantitative precipitation estimates (QPEs) fromsites in California (CA) and Oregon-Washington (OR-WA) are used. During the 172-day period studied, some sites received more than 254 cm (100 in.) of precipitation. The winter season produced many extreme precipitation events, including 90 instances when a site received more than 7.6 cm (3.0 in.) of precipitation in 24 h (i.e., an "event") and 17 events that exceeded 12.7 cm (24 h)-1 [5.0 in. (24 h)-1]. For the 90 extreme events f.7.6 cm (24 h)-1 [3.0 in. (24 h)-1]g, almost 90% of all the 270 QPFs (days 1-3) were biased low, increasingly so with greater lead time. Of the 17 observed events exceeding 12.7 cm (24 h)-1 [5.0 in. (24 h)-1], only 1 of those events was predicted to be that extreme. Almost all of the extreme events correlated with the presence of atmospheric river conditions. Total seasonal QPF biases for all events fi.e., $0.025 cm (24 h)-1 [0.01 in. (24 h)-1]g were sensitive to local geography and were generally biased low in the California-Nevada River Forecast Center (CNRFC) region and high in the Northwest River Forecast Center(NWRFC) domain. The low bias in CA QPFs improved with shorter forecast lead time and worsened for extreme events. Differences were also noted between the CNRFC and NWRFC in terms of QPF and the frequency of extreme events. A key finding from this study is that there were more precipitation events .7.6 cm (24 h)-1 [3.0 in. (24 h)21] in CA than in OR-WA. Examination of 422 Cooperative Observer Program (COOP) sites in the NWRFC domain and 400 in the CNRFC domain found that the thresholds for the top 1% and top 0.1%of precipitation events were 7.6 cm (24 h)21 [3.0 in. (24 h)-1] and 14.2 cm (24 h)-1 [5.6 in. (24 h)-1] or greater for the CNRFC and only 5.1 cm (24 h)-1 [2.0 in. (24 h)-1] and 9.4 cm (24 h)-1 [3.7 in. (24 h)-1] for the NWRFC, respectively. Similar analyses for all NWS RFCs showed that the threshold for the top 1% of events varies from;3.8 cm (24 h)-1 [1.5 in. (24 h)-1] in the Colorado Basin River Forecast Center (CBRFC) to~5.1 cm (24 h)-1 [3.0 in. (24 h)-1] in the northern tier of RFCs and;7.6 cm (24 h)-1 [3.0 in. (24 h)-1] in both the southern tier and the CNRFC. It is recommended that NWS QPF performance in the future be assessed for extreme events using these thresholds. ?? 2010 American Meteorological Society.

Journal of Hydrometeorology↗

USGS2009

Modelling passive margin sequence stratigraphy

We have modelled stratigraphic sequences to aid in deciphering the sedimentary response to sea-level change. Sequence geometry is found to be most sensitive to sea level, but other factors, including subsidence rate and sediment supply, can produce similar changes. Sediment loading and compaction also play a major role in generating accommodation, a factor often neglected in sequence-stratigraphic models. All of these parameters can control whether a type 1 or type 2 sequence boundary is produced. The models indicate that variations in margin characteristics produce systematic shifts in sequence boundary timing and systems tract distribution. The timing of the sequence boundary formation and systems tracts may differ by up to one-half of a sea-level cycle. Thus correlative sequence boundaries will not be synchronous. While rates of sea-level change may exceed the rate of thermal subsidence, isostasy and compaction may amplify the rate of total subsidence to several times greater than the thermal subsidence. Thus, total subsidence does not vary uniformly across the margin since it is modified by the sediment load. The amplitude of sea-level changes cannot be determined accurately without accounting for the major processes that affect sediment accumulation. Backstripping of a seismic line on the New Jersey margin is used to reconstruct continental margin geometry. The reconstructions show that the pre-existing ramp-margin geometry, rather than sea level, controls clinoform heights and slopes and sedimentary bypass. Backstripping also reveals progressive deformation of sequences due to compaction. Further work is still needed to understand quantitatively the role of sea level and the tectonic and sedimentary processes controlling sequence formation and influencing sequence architecture.

Book chapter↗