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AGU Research Spotlight (Jun 29-Jul 05, 2018)

2018-07-05 15:27:20

I.Climate Change

1.Toward Standardized Data Sets for Climate Model Experimentation

A new initiative collects, archives, and documents climate forcing data sets to support coordinated modeling activities that study past, present, and future climates.


2.Climate Change Is Making Night-Shining Clouds More Visible

New research suggests noctilucent clouds are a sign that human-caused climate change is affecting Earth’s middle atmosphere


II.Science Policy & Funding

1.Trumps Ocean Policy Order Draws Ire from Conservation Groups

The executive order gives nods to science and the environment but focuses on resource development and national security.


III.Ocean Sciences

1.Exploring the Interplay Between Ocean Eddies and the Atmosphere

Ocean Mesoscale Eddy Interactions with the Atmosphere: A CLIVAR Workshop; Portland, Oregon, 17–18 February 2018



1.Dark and Stormy: How More Rainfall Leads to Warm and Murky Lakes

Reduced clarity in two northeastern Pennsylvania lakes has resulted in warmer surface water and cooler bottom water despite stable regional air temperatures during the past 3 decades.


2.Upper Estuaries Found to Be Significant Blue Carbon Sink

Inland from the seagrass and salt marsh ecosystems that border the ocean, upper estuaries store more carbon than previously realized and could play an important role in mitigating climate change.


V.Geophysical Research Letters

1.Changes in MaddenJulian Oscillation precipitation and wind variance under global warming

The Madden‐Julian oscillation (MJO) is the leading mode of tropical intraseasonal variability, having profound impacts on many weather and climate phenomena across the tropics and extratropics. Previous studies using a limited number of models have suggested complex changes in MJO activity in a warmer climate. While most studies have argued that MJO precipitation amplitude will increase in a future warmer climate, others note that this is not necessarily the case for MJO wind variability. This distinction is important since MJO wind fluctuations are responsible for producing remote impacts on extreme weather through teleconnections. In this study, we examine projected changes of MJO precipitation and wind variance at the end of the 21st Century in Representative Concentration Pathway 8.5 (RCP8.5) using the multi‐model Coupled Model Intercomparison Project phase 5 (CMIP5) dataset. Under global warming, most models show an increase in MJO band precipitation variance, while wind variability decreases. The discrepancy between MJO precipitation and wind variance changes under global warming is shown to be due to increases in tropical static stability in a warmer climate. The multi‐model mean shows a 20% increase in both the 500 hPa vertical tropical dry static energy gradient and the ratio of intra‐seasonal precipitation to 500 hPa omega fluctuations, consistent with scaling by weak temperature gradient theory. These results imply that tropical static stability increases may weaken the MJO's ability to influence extreme events in future warmer climate by weakening wind teleconnections, even though MJO precipitation amplitude may increase.


2.Interplate coupling state at the NanseiShoto (Ryukyu) Trench, Japan, deduced from seafloor crustal deformation measurements

We performed observations of seafloor crustal deformation employing the GNSS/Acoustic technique at two stations installed at about 45 and 70 km from the axis of the Nansei‐Shoto (Ryukyu) Trench, to the southeast off the Okinawa Main Island. The observations for three‐and six‐year survey periods indicate that the two stations moved landward, in the opposite direction to the trench, by 63 mm/y and 21 mm/y relative to the Ryukyu Arc, suggesting interplate coupling around the stations. The observational results reveal the strong coupling state on the plate interface with coupling ratios of 0.9–1.0 at the slab depths of 10–13 km, or 0.7–0.8 at slab depth ranging from 13 km up to the seafloor. The strongly coupled segment completely coincides with the source area of the 1791 tsunami event and does not overlap with the activity area of slow‐slip events.


3.The relation between the seasonal changes in jet characteristics and the Pacific Midwinter Minimum in eddy activity

This study relates the occurrence of the midwinter minimum in eddy activity over the North Pacific with the seasonality in jet characteristics. During winter, the Pacific jet core is typically around latitude 32°N, and has features of a merged subtropical‐eddy driven jet. On the other hand, during transition seasons, the jet is at higher latitudes (≈40°N,) and resembles more an eddy driven jet. We find that these differences in jet characteristics play a role in the occurrence of the midwinter minimum. It is found that a midwinter minimum‐like behaviour in eddy activity, as observed, is obtained in idealized simulations where zonally‐symmetric temperature profiles are adjusted so as to mimic the seasonality of longitudinally‐averaged temperature observed across the North Pacific. Furthermore, we find both in reanalysis data and in the idealized simulations that a poleward shift of the January jet leads to an increase in eddy kinetic energy (EKE).


VI.AGU Blogs

1.Nioghalvfjerdsbr? 70 km+ Long Supraglacial stream, Greenland’s Longest?

I first observed the impressive discharge and length of the supraglacial streams working on Jakobshavn Glacier more than 30 years ago.The longest persistent supraglacial stream in Greenland at present that I am aware of is on Nioghalvfjerdsbr(79 Glacier).The longest streams will occur on glaciers with low slopes in the ablation zone and limited crevassing, suggesting an extended region of compressive flow. The compressive flow and low slope also would help suppress moulin formation.Rignot et al (1997)first noted that flux from glaciers in this region was 3.5x the iceberg production due primarily to ice loss from basal melt, Nioghalvfjerdsbr has a 20 km wide ice shelf, and the bed remains below sea level over a distance of 150 km upstream from the grounding line, and 200 km inland of the calving front, as indicatedBamber (2013).The basal melt rate in this reach is comparatively low less than 10 m per year maximum and ~5 m per year average seen in figure 2 fromWilson et al (2017).



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