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AGU Research Spotlight (Feb 17-Feb 23, 2017)

2017-02-24 09:37:24

I. Atmospheric Sciences

1. "The Blob" of Abnormal Conditions Raised Western U.S. Ozone Levels

The findings suggest broad-scale climate patterns play a role in air quality and human health.


II. Science Policy

1. Climate Rules on Chopping Block, Says Trump EPA Transition Head

Myron Ebell, whose transition role has ended, denied that President Donald Trump's agency appointees or nominees are antiscience. They're "willing to find out the best science," he said.


III. Hydrology, Cryosphere & Earth Surface

1. Small Storms Over Time Can Cost More Than Extreme Events

Researchers find rising long-term impact of climate change on American cities.


2. Colorado River Flows Will Keep Shrinking as Climate Warms

New study finds that even with more rain, drought periods as long as several decades are likely to occur in the near future.


3. Revived Climate Change Forum Focuses on Threats to Human Health

Public health and environmental organizations brought together by former vice president Al Gore held a pared-down meeting to replace a canceled one.


IV. Geochemistry, Mineralogy, Volcanology

1. Synthesizing Our Understanding of Earth's Deep Carbon

The Deep Carbon Observatory is entering a new phase, in which it will integrate 10 years of discoveries into an overarching model to benefit the scientific community and a wider public.


V. Ocean Sciences

1. What Proportion of River Nutrients Reaches the Open Sea?

Results of the first geographically based estimates of river nutrient supply indicate that 75% of dissolved nitrogen and 80% of phosphorus reach the open ocean.


2. Mounting Litter Spotted on Arctic Seafloor

At one location near Greenland, the density of undersea trash leaped by a factor of 23 in a decade.


VI. Geophysical Research Letters

1. A new record of Atlantic sea surface salinity from 1896 to 2013 reveals the signatures of climate variability and long-term trends

Sea surface salinity (SSS) is a major ocean circulation component and indicator of the hydrological cycle. Here we investigate an unprecedented Atlantic SSS compilation from 1896 to 2013 and analyze the main modes of SSS decadal variability. Using principal component analysis, we find that the low-latitude (tropical and subtropical) Atlantic and the subpolar Atlantic have distinct variability. Subpolar and low-latitude SSS are negatively correlated, with subpolar anomalies leading low-latitude anomalies by about a decade. Subpolar SSS varies in phase with the Atlantic Multidecadal Oscillation (AMO), whereas low-latitude SSS varies in phase with the North Atlantic Oscillation (NAO). Additionally, northern tropical SSS is anticorrelated with Sahel rainfall, suggesting that SSS reflects the Intertropical Convergence Zone latitude. The 1896–2013 SSS trend shows amplification of the mean SSS field, with subpolar freshening and low-latitude salinification. The AMO and NAO have little effect on the long-term trend but contribute to the trend since 1970.


2. The relative contribution of waves, tides, and nontidal residuals to extreme total water levels on U.S. West Coast sandy beaches

To better understand how individual processes combine to cause flooding and erosion events, we investigate the relative contribution of tides, waves, and nontidal residuals to extreme total water levels (TWLs) at the shoreline of U.S. West Coast sandy beaches. Extreme TWLs, defined as the observed annual maximum event and the simulated 100 year return level event, peak in Washington, and are on average larger in Washington and Oregon than in California. The relative contribution of wave-induced and still water levels (SWL) to the 100 year TWL event is similar to that of the annual maximum event; however, the contribution of storm surge to the SWL doubles across events. Understanding the regional variability of TWLs will lead to a better understanding of how sea level rise, changes in storminess, and possible changes in the frequency of major El Ni?os may impact future coastal flooding and erosion along the U.S. West Coast and elsewhere.


3. Negative first stroke leader characteristics in cloud-to-ground lightning over land and ocean

We examine downward leader characteristics for negative first return strokes, along with estimated first stroke peak currents, for lightning occurring over land and ocean reported by the U.S. National Lightning Detection Network (NLDN). For the first time, to the best of our knowledge, we report independent evidence that supports the observations by lightning locating systems of higher first stroke peak currents for lightning occurring over ocean than land. We analyzed lightning occurring in five circular regions, each with 50?km diameter. In western Florida, the median stepped-leader duration was 17% shorter over ocean than over land and in eastern Florida the median durations were 21% and 39% shorter over two oceanic regions than over land.


4. Observations of amplified roughness from crystal accretion in the sub-ice ocean boundary layer

Ice crystal accretion on the underside of sea ice and ice shelves, a signature of pressure-induced supercooling, has the potential to alter the energy balance in the ocean boundary layer through enhanced hydrodynamic roughness. Here we present estimates of crystal-driven ocean boundary layer roughness in supercooled water beneath sea ice adjacent to the McMurdo/Ross Ice Shelf. Data were collected from four sites in McMurdo Sound, Antarctica, between 2007 and 2015, and represent a range of ice shelf-affected conditions. The results show that drag of the rough ice underside in the presence of platelets is 6–30 times larger than typical levels homogeneously applied in ice-ocean interaction models. The crystal-enhanced drag promotes increased entrainment into the boundary layer from the upper ocean, which has the potential to affect ice shelf evolution and sea ice growth through enhanced turbulent exchange of heat and momentum.


5. Atlantic meridional heat transports computed from balancing Earth's energy locally

The Atlantic Meridional Overturning Circulation plays a major role in moving heat and carbon around in the ocean. A new estimate of ocean heat transports for 2000 through 2013 throughout the Atlantic is derived. Top-of-atmosphere radiation is combined with atmospheric reanalyses to estimate surface heat fluxes and combined with vertically integrated ocean heat content to estimate ocean heat transport divergence as a residual. Atlantic peak northward ocean heat transports average 1.18?±?0.13?PW (1 sigma) at 15°N but vary considerably in latitude and time. Results agree well with observational estimates at 26.5°N from the RAPID array, but for 2004–2013 the meridional heat transport is 1.00?±?0.11?PW versus 1.23?±?0.11?PW for RAPID. In addition, these results have no hint of a trend, unlike the RAPID results. Strong westerlies north of a meridian drive ocean currents and an ocean heat loss into the atmosphere that is exacerbated by a decrease in ocean heat transport northward.


6. Connecting ocean heat transport changes from the midlatitudes to the Arctic Ocean

Under greenhouse warming, climate models simulate a weakening of the Atlantic Meridional Overturning Circulation and the associated ocean heat transport at midlatitudes but an increase in the ocean heat transport to the Arctic Ocean. These opposing trends lead to what could appear to be a discrepancy in the reported ocean contribution to Arctic amplification. This study clarifies how ocean heat transport affects Arctic climate under strong greenhouse warming using a set of the 21st century simulations performed within the Coupled Model Intercomparison Project. The results suggest that a future reduction in subpolar ocean heat loss enhances ocean heat transport to the Arctic Ocean, driving an increase in Arctic Ocean heat content and contributing to the intermodel spread in Arctic amplification. The results caution against extrapolating the forced oceanic signal from the midlatitudes to the Arctic.


7. The temperature-ballast hypothesis explains carbon export efficiency observations in the Southern Ocean

Carbon export from the Southern Ocean exerts a strong control on the ocean carbon sink, yet recent observations from the region demonstrate poorly understood relationships in which carbon export efficiency is weakly related to temperature. These observations conflict with traditional theory where export efficiency increases in colder waters. A recently proposed “temperature-ballast hypothesis” suggests an explanatory mechanism where the effect of temperature-dependent respiration is masked by variation in particle-ballast as upwelling waters move northward from Antarctica. We use observations and statistical models to test this mechanism and find positive support for the hypothesized temperature-ballast interactions. Best fitting models indicate a significant relation between export efficiency and silica-ballast while simultaneously revealing the expected inverse effect of temperature once ballast is accounted for. These findings reconcile model predictions, metabolic theory, and carbon export observations in the Southern Ocean and have consequences for how the ocean carbon sink responds to climate change.


VII. AGU Blogs

1. Ancient cave reveals recent droughts in the Middle East were most severe for over a millennium

A stalagmite collected from a remote cave in the Middle East has revealed that recent droughts there were more severe than previously thought, and therefore possibly an important contributing factor for the turmoil in Syria. A research team traveled to Iraq to collect the stalagmite and used it to present the first ever detailed climate reconstruction of the Fertile Crescent extending back 2,400 years.


2. How Do Climate Models Work? Answer Here.

Keith Dixon is one of my go-to people when I have a question about climate modelling, so when Climate Central said they were going to host a webinar with Keith, I begged them to record it. They did! Now, this was done for meteorologists, so a bit of a geek alert here, but I think you will find it fascinating, even if you have no atmospheric science background.


3. The Fake Science News In Nearly Every Newspaper Today

There’s been a lot of talk about fake news recently, and there are definitely some media outlets that seem to be major purveyors of it. The Daily Mail in London is a good example. I don’t think I’ve ever seen a story about science that they got right. Not one. Now, I love the Washington Post, so don’t get me wrong here, but I found a glaring chunk of outrageously …


4. The Real Surprise Behind the 3rd Hottest January on Record

The planet’s temperature oscillates a little, between El Nino events and La Nina events. El Nino’s warm the planet a few tenths of a degree, while La Nina events cool it by about that much. The stronger the event the bigger the effect, so a strong El Nino makes it more likely that we will see a new hottest month on record, while a strong La Nina makes that more unlikely.


5. The first 100 days of climate science

How will you remember the first 100 days in office of the 45th President of the United States? Climate Central, an organization of scientists and journalists that disseminates information about climate change and human impacts, is highlighting one science and/or climate fact per day for the first 100 days of the presidency. The organization is setting out “to underscore the value of science and rational approaches to policy” and “provide key scientific context of the choices humanity faces and what policy actions (or inactions) mean.”


6. Philadelphia’s Whaling Wall heading for extinction

“I try to save as many of my murals as I can because it’s not just public art — it’s art that has a message of conservation”



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