101 research outputs found
Impacts of extreme 2013â2014 winter conditions on Lake Michigan's fall heat content, surface temperature, and evaporation
Since the late 1990s, the Laurentian Great Lakes have experienced persistent low water levels and above average overâlake evaporation rates. During the winter of 2013â2014, the lakes endured the most persistent, lowest temperatures and highest ice cover in recent history, fostering speculation that overâlake evaporation rates might decrease and that water levels might rise. To address this speculation, we examined interseasonal relationships in Lake Michigan's thermal regime. We find pronounced relationships between winter conditions and subsequent fall heat content, modest relationships with fall surface temperature, but essentially no correlation with fall evaporation rates. Our findings suggest that the extreme winter conditions of 2013â2014 may have induced a shift in Lake Michigan's thermal regime and that this shift coincides with a recent (and ongoing) rise in Great Lakes water levels. If the shift persists, it could (assuming precipitation rates remain relatively constant) represent a return to thermal and hydrologic conditions not observed on Lake Michigan in over 15âyears.Key PointsLake Michigan has been in an altered thermal regime since the late 1990sThe 2013â2014 winter may return Lake Michigan to preâ1998 thermal conditionsHydrological impacts of the 2013â2014 cold winter remain unclearPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112001/1/grl52850.pd
Cold Water and High Ice Cover on Great Lakes in Spring 2014
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108350/1/eost2014EO340001.pd
Simulating Impacts of Precipitation on Ice Cover and Surface Water Temperature Across Large Lakes
Precipitation impacts on ice cover and water temperature in the Laurentian Great Lakes were examined using stateâofâtheâart coupled iceâhydrodynamic models. Numerical experiments were conducted for the recent anomalously cold (2014â2015) and warm (2015â2016) winters that were accompanied by high and low ice coverage over the lakes, respectively. The results of numerical experiments showed that snow cover on the ice, which is the manifestation of winter precipitation, reduced the total ice volume (or mean ice thickness) in all of the Great Lakes, shortened the ice duration, and allowed earlier warming of water surface. The reduced ice volume was due to the thermal insulation of snow cover. The surface albedo was also increased by snow cover, but its impact on the delay the melting of ice was overcome by the thermal insulation effect. During major snowstorms, snowfall over the open lake caused notable cooling of the water surface due to latent heat absorption. Overall, the sensible heat flux from rain in spring and summer was found to have negligible impacts on the water surface temperature. Although uncertainties remain in overlake precipitation estimates and modelâs representation of snow on the ice, this study demonstrated that winter precipitation, particularly snowfall on the ice and water surfaces, is an important contributing factor in Great Lakes ice production and thermal conditions from late fall to spring.Plain Language SummarySnow and rain impact on ice cover and water temperature in large lakes were studied using a computational model for an example of the Laurentian Great Lakes. It was found that snow cover increased the reflection of solar radiation but at the same time prevented lake ice from the growing, resulting in less formation of ice and slightly earlier melting. The earlier ice melting also allowed earlier warming of the water surface in spring. Major snowstorms caused slight cooling in the water surface temperature because snowflakes absorbed heat when it touched the water surface to melt. On the other hand, warmer rain barely changed the water surface temperature during summer.Key PointsPrecipitation impacts on Great Lakes ice cover and water temperature were evaluated using a coupled iceâhydrodynamic modelThe model results showed that snow cover on the ice reduced the net production of ice, which resulted in earlier decay of ice coverThe model results showed that snowfall cooled the water surface notably through latent heat absorption during stormsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155461/1/jgrc23973.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155461/2/jgrc23973_am.pd
Identifying streamgage networks for maximizing the effectiveness of regional water balance modeling
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98795/1/wrcr20233.pd
Radiative corrections to the Chern-Simons term at finite temperature in the noncommutative Chern-Simons-Higgs model
By analyzing the odd parity part of the gauge field two and three point
vertex functions, the one-loop radiative correction to the Chern-Simons
coefficient is computed in noncommutative Chern-Simons-Higgs model at zero and
at high temperature. At high temperature, we show that the static limit of this
correction is proportional to but the first noncommutative correction
increases as . Our results are analytic functions of the
noncommutative parameter.Comment: Revised version with a new section on the gauge field three point
vertex function adde
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Evaluating and improving modeled turbulent heat fluxes across the North American Great Lakes
Turbulent fluxes of latent and sensible heat are important physical processes
that influence the energy and water budgets of the North American Great
Lakes. These fluxes can be measured in situ using eddy covariance techniques
and are regularly included as a component of lakeâatmosphere models. To help
ensure accurate projections of lake temperature, circulation, and regional
meteorology, we validated the output of five algorithms used in three popular
models to calculate surface heat fluxes: the Finite Volume Community Ocean
Model (FVCOM, with three different options for heat flux algorithm), the
Weather Research and Forecasting (WRF) model, and the Large Lake
Thermodynamic Model. These models are used in research and operational
environments and concentrate on different aspects of the Great Lakes'
physical system. We isolated only the code for the heat flux algorithms from
each model and drove them using meteorological data from four over-lake
stations within the Great Lakes Evaporation Network (GLEN), where eddy
covariance measurements were also made, enabling co-located comparison. All
algorithms reasonably reproduced the seasonal cycle of the turbulent heat
fluxes, but all of the algorithms except for the Coupled OceanâAtmosphere
Response Experiment (COARE) algorithm showed notable overestimation of the
fluxes in fall and winter. Overall, COARE had the best agreement with eddy
covariance measurements. The four algorithms other than COARE were altered by
updating the parameterization of roughness length scales for air temperature
and humidity to match those used in COARE, yielding improved agreement
between modeled and observed sensible and latent heat fluxes.</p
A Minimal Threshold of c-di-GMP Is Essential for Fruiting Body Formation and Sporulation in Myxococcus xanthus
Generally, the second messenger bis-(3â-5â)-cyclic dimeric GMP (c-di-GMP) regulates the switch between motile and sessile lifestyles in bacteria. Here, we show that c-di-GMP is an essential regulator of multicellular development in the social bacterium Myxococcus xanthus. In response to starvation, M. xanthus initiates a developmental program that culminates in formation of spore-filled fruiting bodies. We show that c-di-GMP accumulates at elevated levels during development and that this increase is essential for completion of development whereas excess c-di-GMP does not interfere with development. MXAN3735 (renamed DmxB) is identified as a diguanylate cyclase that only functions during development and is responsible for this increased c-di-GMP accumulation. DmxB synthesis is induced in response to starvation, thereby restricting DmxB activity to development. DmxB is essential for development and functions downstream of the Dif chemosensory system to stimulate exopolysaccharide accumulation by inducing transcription of a subset of the genes encoding proteins involved in exopolysaccharide synthesis. The developmental defects in the dmxB mutant are non-cell autonomous and rescued by co-development with a strain proficient in exopolysaccharide synthesis, suggesting reduced exopolysaccharide accumulation as the causative defect in this mutant. The NtrC-like transcriptional regulator EpsI/Nla24, which is required for exopolysaccharide accumulation, is identified as a c-diGMP receptor, and thus a putative target for DmxB generated c-di-GMP. Because DmxB can beâat least partiallyâfunctionally replaced by a heterologous diguanylate cyclase, these results altogether suggest a model in which a minimum threshold level of c-di-GMP is essential for the successful completion of multicellular development in M. xanthus
The Impact of Error-Management Climate, Error Type and Error Originator on Auditorsâ Reporting Errors Discovered on Audit Work Papers
We examine factors affecting the auditorâs willingness to report their own or their peersâ self-discovered errors in working papers subsequent to detailed working paper review. Prior research has shown that errors in working papers are detected in the review process; however, such detection rates only rarely exceed 50% of the seeded errors. Hence, measures that encourage auditors to be alert to their own (or their peersâ) potential errors any time they revisit the audit working papers may be valuable in detecting such residual errors and potentially correcting them before damage occurs to the audit firm or its client. We hypothesize that three factors affect the auditorâs willingness to report post detailed review discovered errors: the local office error-management climate (open versus blame), the type of error (mechanical versus conceptual) and who committed the error (the individual who committed the error (self) or a peer). Local office error-management climate is said to be open and supportive where errors and mistakes are accepted as part of everyday life as long as they are learned from and not repeated. In alternative, a blame error-management climate focuses on a âget it right the first timeâ culture where mistakes are not tolerated and blame gets attached to those admitting to or found committing such errors. We find that error-management climate has a significant overall effect on auditor willingness to report errors, as does who committed the error originally. We find both predicted and unpredicted significant interactions among the three factors that qualify these observed significant main effects. We discuss implications for audit practice and further research
On-line bioaffinity-electrospray mass spectrometry for simultaneous detection, identification, and quantification of protein-ligand interactions
Latitude and lake size are important predictors of over-lake atmospheric stability: Atmospheric Stability Above Lakes
Turbulent fluxes across the airâwater interface are integral to determining lake heat budgets, evaporation, and carbon emissions from lakes. The stability of the atmospheric boundary layer (ABL) influences the exchange of turbulent energy. We explore the differences in overâlake ABL stability using data from 39 globally distributed lakes. The frequency of unstable ABL conditions varied between lakes from 71 to 100% of the time, with average air temperatures typically several degrees below the average lake surface temperature. This difference increased with decreasing latitude, resulting in a more frequently unstable ABL and a more efficient energy transfer to and from the atmosphere, toward the tropics. In addition, during summer the frequency of unstable ABL conditions decreased with increasing lake surface area. The dependency of ABL stability on latitude and lake size has implications for heat loss and carbon fluxes from lakes, the hydrologic cycle, and climate change effects
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