I.Climate Change

1. Is There a Greenhouse Effect in the Ionosphere, Too? Likely Not

Controversial observations of long-term changes in the ionosphere appear to be explained by the Sun’s 11-year cycle of activity, not human greenhouse gas emissions.

https://eos.org/research-spotlights/is-there-a-greenhouse-effect-in-the-ionosphere-too-likely-not

2. Understanding a Changing West Antarctic Peninsula

The 1st Workshop of the SOOS WAP Working Group; Cambridge, United Kingdom, 15–16 May 2017 In Icy Waters: The Future of Marine Biogeochemical Research off the West Antarctic Peninsula; Chicheley, United Kingdom, 17–18 May 2017

https://eos.org/meeting-reports/understanding-a-changing-west-antarctic-peninsula

3. Unusual Antarctic Weather Affected Outcome of South Pole Race

New research shows warm weather and good conditions were a boon to the Norwegian explorers who first reached the Pole but hindered the progress of a competing British party.

https://eos.org/scientific-press/unusual-antarctic-weather-affected-outcome-of-south-pole-race

4. How Do Clouds React to Regional Warming?

Researchers illuminate how and why cloud feedbacks depend on spatial patterns of global warming.

https://eos.org/research-spotlights/how-do-clouds-react-to-regional-warming

II. Hazards & Disasters

1. Sooty Bird Bellies Yield Insights into Historical Air Pollution

A new study mined museum collections to investigate just how sooty the air in the United States has been for the past 135 years.

https://eos.org/articles/sooty-bird-bellies-yield-insights-into-historical-air-pollution

2. Volcanic Unrest at Mauna Loa, Earth’s Largest Active Volcano

Mauna Loa is stirring—is a major eruption imminent? Comparisons with previous eruptions paint a complicated picture.

https://eos.org/features/volcanic-unrest-at-mauna-loa-earths-largest-active-volcano

3. El Niño and 2016 Ecuador Earthquake Worsened Zika Outbreak

Researchers suggest the earthquake left more people exposed to disease-carrying mosquitos and climate variability during the 2014–2016 El Niño created more favorable mosquito breeding grounds.

https://eos.org/scientific-press/el-nino-and-2016-ecuador-earthquake-worsened-zika-outbreak

III. Biogeosciences

1. Stories in the Soil

A series of field experiments in the U.S. Midwest is investigating how past, present, and future human activities and climate affect the health of soil.

https://eos.org/editors-vox/stories-in-the-soil

2. The Microphysics of Squall Lines

Scientists tracked the distribution of raindrops of different sizes as a row of thunderstorms formed by a cold front developed and intensified over eastern China.

https://eos.org/research-spotlights/the-microphysics-of-squall-lines

IV.Geology & Geophysics

1. Ten Mesmerizing Geophysical Maps That Double as Works of Art

From tiny seafloor features in the Gulf of Mexico to craters pocking the surface of Mars, the details on these maps captivate and fascinate.

https://eos.org/features/ten-mesmerizing-geophysical-maps-that-double-as-works-of-art

2. Thirteen Innovative Ways Humans Use Drones

From the bottom of acid lakes to up in the sky, autonomous vehicles are changing the way scientists view and study Earth.

https://eos.org/features/thirteen-innovative-ways-humans-use-drones

V.Space & Planets

1. A Wake-up Call from the Sun

A sudden burst of activity from the Sun in early September 2017 caused a wide range of space weather effects at Earth.

https://eos.org/editors-vox/a-wake-up-call-from-the-sun

2.Angles of Plasma Ropes near Mars Point to Different Origins

Variation in the orientation of flux rope features in Mars’s magnetotail suggests that some of them form on the planet’s Sun-facing side and travel to the night side.

https://eos.org/research-spotlights/angles-of-plasma-ropes-near-mars-point-to-different-origins

VI.Geophysical Research Letters

1. Effect of Snow Salinity on CryoSat-2 Arctic First-Year Sea Ice Freeboard Measurements

The European Space Agency's CryoSat-2 satellite mission provides radar altimeter data that are used to derive estimates of sea ice thickness and volume. These data are crucial to understanding recent variability and changes in Arctic sea ice. Sea ice thickness retrievals at the CryoSat-2 frequency require accurate measurements of sea ice freeboard, assumed to be attainable when the main radar scattering horizon is at the snow/sea ice interface. Using an extensive snow thermophysical property dataset from late winter conditions in the Canadian Arctic, we examine the role of saline snow on first-year sea ice (FYI), with respect to its effect on the location of the main radar scattering horizon, its ability to decrease radar penetration depth, and its impact on FYI thickness estimates. Based on the dielectric properties of saline snow commonly found on FYI, we quantify the vertical shift in the main scattering horizon. This is found to be approximately 0.07 m. We propose a thickness-dependent snow salinity correction factor for FYI freeboard estimates. This significantly reduces CryoSat-2 FYI retrieval error. Relative error reductions of ~11% are found for an ice thickness of 0.95 m and ~25% for 0.7 m. Our method also helps to close the uncertainty gap between SMOS and CryoSat-2 thin ice thickness retrievals. Our results indicate that snow salinity should be considered for FYI freeboard estimates.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074506/full

2. Multidecadal Weakening of Indian Summer Monsoon Circulation Induces an Increasing Northern Indian Ocean Sea Level

North Indian Ocean sea level has shown significant increase during last three to four decades. Analyses of long-term climate data sets and ocean model sensitivity experiments identify a mechanism for multidecadal sea level variability relative to global mean. Our results indicate that North Indian Ocean sea level rise is accompanied by a weakening summer monsoon circulation. Given that Indian Ocean meridional heat transport is primarily regulated by the annual cycle of monsoon winds, weakening of summer monsoon circulation has resulted in reduced upwelling off Arabia and Somalia and decreased southward heat transport, and corresponding increase of heat storage in the North Indian Ocean. These changes in turn lead to increased retention of heat and increased thermosteric sea level rise in the North Indian Ocean, especially in the Arabian Sea. These findings imply that rising North Indian Ocean sea level due to weakening of monsoon circulation demands adaptive strategies to enable a resilient South Asian population.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074706/full

3. The Importance of Upper Mantle Heterogeneity in Generating the Indian Ocean Geoid Low

One of the most pronounced geoid lows on Earth lies in the Indian Ocean just south of the Indian peninsula. Several theories have been proposed to explain this geoid low, most of which invoke past subduction. Some recent studies have also argued that high-velocity anomalies in the lower mantle coupled with low-velocity anomalies in the upper mantle are responsible for these negative geoid anomalies. However, there is no general consensus regarding the source of this particular anomaly. We investigate the source of this geoid low by using models of density-driven mantle convection. Our study is the first to successfully explain the occurrence of this anomaly using a global convection model driven by present-day density anomalies derived from tomography. We test various tomography models in our flow calculations with different radial and lateral viscosity variations. Some of them produce a fairly high correlation to the global geoid, but only a few (SMEAN2, GyPSuM, SEMUCB, and LLNL-JPS) could match the precise location and pattern of the geoid low in the Indian Ocean. The source of this low stems from a low-density anomaly stretching from a depth of 300 km down to ～900 km in the northern Indian Ocean region.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075392/full

4. The Enhancement of Neutral Metal Na Layer Above Thunderstorms

Atomic sodium (Na) is one of the major meteoric species existing as layers of atoms in the mesosphere/lower thermosphere (MLT) at altitudes of 80–105 km and atomic ions at higher altitudes. As the boundary between neutral atmosphere and ionosphere, the MLT region is of particular interest because it is influenced by the mesoscale convective weather and thunderstorms from below and exposed to solar photons from above. There has been great interest on the atmosphere-ionosphere coupling, and numerous studies have been reported on the connection between thunderstorms and the ionosphere. However, the influence of thunderstorms on metallic species, which would significantly enhance our understanding of how Earth's atmosphere interacts with its ionosphere and studying the chemistry and physics of the MLT region, has rarely been studied. Here we present observational results on a statistical basis showing evidence that thunderstorm activities can affect the metal layer, by identifying a statistically significant enhancement of the neutral metal Na layer above thunderstorms at Haikou, China (20.0°N, 110.3°E). The thunderstorm-generated gravity waves and electric field effects could be the mechanisms responsible for the lightning-associated enhancement of Na layer.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074977/full

5. On the Yield Strength of Oceanic Lithosphere

The yield strength of oceanic lithosphere determines the mode of mantle convection in a terrestrial planet, and low-temperature plasticity in olivine aggregates is generally believed to govern the plastic rheology of the stiffest part of lithosphere. Because, so far, proposed flow laws for this mechanism exhibit nontrivial discrepancies, we revisit the recent high-pressure deformation data of Mei et al. (2010) with a comprehensive inversion approach based on Markov chain Monte Carlo sampling. Our inversion results indicate that the uncertainty of the relevant flow law parameters is considerably greater than previously thought. Depending on the choice of flow law parameters, the strength of oceanic lithosphere would vary substantially, carrying different implications for the origin of plate tectonics on Earth. To reduce the flow law ambiguity, we suggest that it is important to establish a theoretical basis for estimating macroscopic stress in high-pressure experiments and also to better utilize marine geophysical observations.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075043/full

6. Are Simulated and Observed Twentieth Century Tropical Pacific Sea Surface Temperature Trends Significant Relative to Internal Variability?

Historical trends in the tropical Pacific zonal sea surface temperature gradient (SST gradient) are analyzed herein using 41 climate models (83 simulations) and 5 observational data sets. A linear inverse model is trained on each simulation and observational data set to assess if trends in the SST gradient are significant relative to the stationary statistics of internal variability, as would suggest an important role for external forcings such as anthropogenic greenhouse gasses. None of the 83 simulations have a positive trend in the SST gradient, a strengthening of the climatological SST gradient with more warming in the western than eastern tropical Pacific, as large as the mean trend across the five observational data sets. If the observed trends are anthropogenically forced, this discrepancy suggests that state-of-the-art climate models are not capturing the observed response of the tropical Pacific to anthropogenic forcing, with serious implications for confidence in future climate projections. There are caveats to this interpretation, however, as some climate models have a significant strengthening of the SST gradient between 1900 and 2013 Common Era, though smaller in magnitude than the observational data sets, and the strengthening in three out of five observational data sets is insignificant. When combined with observational uncertainties and the possibility of centennial time scale internal variability not sampled by the linear inverse model, this suggests that confident validation of anthropogenic SST gradient trends in climate models will require further emergence of anthropogenic trends. Regardless, the differences in SST gradient trends between climate models and observational data sets are concerning and motivate the need for process-level validation of the atmosphere-ocean dynamics relevant to climate change in the tropical Pacific.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074622/full

VII. AGU Blogs

1. UK and Ireland Smacked Hard By Ophelia

My close friends in Wales report the “wheely bins” are all over the place. The obs at Dublin airport show winds have gusted to right at 60 mph during the afternoon and evening, and on Anglesey, in Wales the winds reach 65 mph!

http://blogs.agu.org/wildwildscience/2017/10/16/meteosat-view-ophelia-ireland/

2. Waves in lakes make waves in the Earth

Beneath the peaceful rolling waves of a lake is a rumble, imperceptible to all but seismometers, that ripples into the earth like the waves ripple along the shore.

http://blogs.agu.org/geospace/2017/10/16/waves-in-lakes-make-waves-in-the-earth/

3. The missing mass — what is causing a geoid low in the Indian Ocean?

The Earth's interior is still a mystery to us. While we have sent missions to probe the outer reaches of our Solar system, the deepest boreholes on Earth go down to only a few kilometres. The only way to learn what’s going on deep inside our planet, in the core and the mantle, is by indirect methods.

http://blogs.agu.org/geospace/2017/10/16/missing-mass-causing-geoid-low-indian-ocean/