8 New Research Papers: Climate, Weather, Earth

8 Important New Research Papers!

ASW

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Subject: End of hospitable climate: Recent research

From:    “Lance Olsen” <lance@wildrockies.org>

Date:    Thu, July 24, 2008 12:16 pm

To:      “cmcr-outreach” <cmcr-outreach@vortex.wildrockies.org>

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Public release date: 23-Jul-2008

Geophysical Research Letters (American Geophysical Union)

 

Contact: Peter Weiss

pweiss@agu.org

202-777-7507

 

AGU journal highlights — July 23, 2008

 

1. Fire suppression may have reduced carbon storage in western U.S. forests

 

Active fire suppression since the early twentieth 

century has caused a widespread increase in 

fire-intolerant trees, smaller trees, and the 

density of stems growing on trees within western 

U.S. forests. These factors have created thicker 

forests and are thought to account for much of 

North America’s carbon sink. To better quantify 

changes in aboveground biomass, Fellows and 

Goulden compare California forest inventories 

from the 1930s with those from the 1990s. To 

compare these data, interpolation measures are 

used that result in underestimations of stem 

density and biomass estimates for data from the 

1930s. Nonetheless, the authors find that stem 

density in these conifer forests increased by 34 

percent between 1930 and 1990, reflecting an 

increase in the number of small trees. However, 

aboveground carbon stocks decreased by 26 percent 

because large trees, which contain a 

disproportionate amount of carbon, experienced a 

net loss between the surveys. The authors 

conclude that twentieth-century fire suppression 

and the resulting increase in stand density may 

have decreased, rather than increased, the amount 

of biomass stored in western U.S. forests.

 

Title: Has fire suppression increased the amount 

of carbon stored in western U.S. forests?

 

Authors: Aaron W. Fellows and Michael L. Goulden: 

Department of Earth System Science, University of 

California, Irvine, California, U.S.A..

 

Source: Geophysical Research Letters (GRL) paper 

10.1029/2008GL033965, 2008; 

http://dx.doi.org/10.1029/2008GL033965

 

2. New tracking method reveals giant volcanic clouds’ paths

 

On 17 August 1980, Iceland’s Hekla volcano 

erupted, spewing a sulfur dioxide cloud into the 

north polar stratosphere that reached roughly 15 

kilometers (9 miles) in altitude. Although 

satellites recorded this event, techniques that 

exploit the strong absorption of infrared 

radiation by sulfur dioxide have only recently 

emerged, allowing scientists to reanalyze old 

data to track volcanic gas clouds. Using the 

ultraviolet data collected by the Nimbus 7 Total 

Ozone Mapping Spectrometer and infrared data 

collected by the High Resolution Infrared 

Radiation Sounder (on NOAA’s Television Infrared 

Observation Satellite (TIROS) Operational 

Vertical Sounder), Carn et al. tracked sulfur 

dioxide released by Hekla. They find that the 

eruption emitted about 0.5 to 0.7 teragrams 

(trillions of grams) of sulfur dioxide, which 

later split into three distinct clouds, one of 

which circled the North Pole for 6 days. The 

others drifted across eastern Russia, Alaska, and 

Canada. Through this analysis, the authors show 

that integrated satellite sulfur dioxide 

measurements may be used to test air parcel 

trajectory models used for aviation hazard 

mitigation. This study also highlights the 

potential impacts of Icelandic volcanic eruptions 

on the polar atmosphere and Arctic ozone loss.

 

Title: Circumpolar transport of a volcanic cloud from Hekla (Iceland)

 

Authors: S. A. Carn: Joint Center for Earth 

Systems Technology (NASA/University of Maryland 

Baltimore County), University of Maryland 

Baltimore County, Baltimore, Maryland, U.S.A;

 

A. J. Prata: Atmosphere and Climate Department, 

Norwegian Institute for Air Research (NILU), 

Kjeller, Norway;

 

S. Karlsdóttir: Icelandic Meteorological Office, Reykjavík, Iceland.

 

Source: Journal of Geophysical 

Research-Atmospheres (JGR-D) paper 

10.1029/2008JD009878, 2008; 

http://www.agu.org/journals/pip/jd/2008JD009878-pip.pdf 

This paper is “in press”.

 

3. Frost risks to plants up, and down, in changing climate

 

As climate warms, scientists expect that the 

bud-break and blooming cycles of plants will 

start progressively earlier each year. Most 

studies of the risk associated with early 

blooming use simple increases in monthly mean 

temperatures to represent future climate 

scenarios. However, both the average and the 

variation of daily temperatures are forecast to 

increase in future climate scenarios; such 

variation in temperatures increases the risk that 

early bud-breaks are followed by damaging frost. 

To study such frost risk to vegetation, Rigby and 

Porporato developed a probabilistic model that 

represents bud-break in the context of 

fluctuating but warming temperatures. After 

calibrating this model to temperature data from 

Durham, N. C., the authors find that model 

results show that frost risk is equally sensitive 

to increases in daily temperature fluctuations 

(which serves to increase frost risk) as to 

increases in average temperatures (which serves 

to decrease frost risk).

 

Title: Spring frost risk in a changing climate

 

Authors: J. R. Rigby and Amilcare Porporato: 

Department of Civil and Environmental 

Engineering, Duke University, Durham, North 

Carolina, U.S.A.

 

Source: Geophysical Research Letters (GRL) paper 

10.1029/2008GL033955, 2008; 

http://dx.doi.org/10.1029/2008GL033955

 

4. Martian mineral layers offer tempting clues

 

Clay minerals such as montmorillonite and other 

smectites have been previously detected in 

layered outcrops in and around the Martian 

outflow channel Mawrth Vallis. Wray et al. 

additionally identify kaolinite and oxide 

minerals such as hematite in the Mawrth Vallis 

outcrops and find that these diverse minerals 

occur in distinct stratigraphic horizons, 

implying either that they formed over time under 

different environmental conditions or that they 

have distinctly different sediment sources. The 

authors observe that this pattern of layers 

occurs on both sides of the outflow channel and 

on its floor, with aluminum-rich clay-bearing 

layers typically overlying iron-rich clay 

deposits. This, combined with high-resolution 

topographic data, suggests that the aluminum-rich 

clay-bearing layers are younger than the outflow 

channel and may represent a later sedimentary or 

altered volcanic ash deposit that drapes the 

topography. Because of Mawrth Vallis’s distinct 

layering history, the authors expect that this 

would make a good location for future surface 

missions to Mars to study geologic history and 

ancient habitable environments on Mars.

 

Title: Compositional stratigraphy of clay-bearing 

layered deposits at Mawrth Vallis, Mars

 

Authors: J. J. Wray and S. W Squyres: Department 

of Astronomy, Cornell University, Ithaca, New 

York, U.S.A.;

 

B. L. Ehlmann and J. F. Mustard: Department of 

Geological Sciences, Brown University, 

Providence, Rhode Island, U.S.A.;

 

R. L. Kirk: Astrogeology Program, U.S. Geological 

Survey, Flagstaff, Arizona, U.S.A.

 

Source: Geophysical Research Letters (GRL) paper 

10.1029/2008GL034385, 2008; 

http://dx.doi.org/10.1029/2008GL034385

 

5. Uruguay River flow responds to climate, land-use changes

 

The Uruguay River basin has experienced extensive 

land change during the second half of the 

twentieth century as agricultural area expanded. 

Concurrent with this has been an increase of 

streamflow and precipitation due to atmospheric 

dynamics. To help determine which factor-land use 

change or atmospheric dynamics-has contributed 

more to fluctuations in Uruguay River discharge, 

Saurral et al. study streamflow along the Uruguay 

River using a hydrology model run between 1960 

and 2000 that explicitly accounts for the role of 

land cover. The authors find that increases in 

average streamflow are more likely attributable 

to climatic variations, implying that land use 

changes were not large enough to produce 

appreciable changes in basin runoff. This is 

perhaps because most land changes did not result 

from deforestation but instead involved 

converting grassland (pasture) to crops. However, 

the authors note that basin response, namely, 

that flows at the basin outlet now occur about 2 

days sooner than in the 1960s, appears to be 

attributable solely to land cover change between 

the 1960s and the 1990s.

 

Title: Land use impact on the Uruguay River discharge

 

Authors: Ramiro I. Saurral and Vicente R. Barros: 

Center for Atmospheric and Oceanic Research, 

National Scientific and Technical Research 

Council, University of Buenos Aires, Buenos 

Aires, Argentina; also at Department of 

Atmospheric and Ocean Sciences, University of 

Buenos Aires, Buenos Aires, Argentina;

 

Dennis P. Lettenmaier: Department of Civil and 

Environmental Engineering, University of 

Washington, Seattle, Washington, U.S.A.

 

Source: Geophysical Research Letters (GRL) paper 

10.1029/2008GL033707, 2008; 

http://dx.doi.org/10.1029/2008GL033707

 

6. Reexamining stratosphere effects on lower-atmosphere warming

 

It is well established that the troposphere, the 

atmospheric layer closest to the Earth’s surface, 

significantly influences the circulation of the 

stratosphere, the layer above the troposphere. 

The alternate possibility, that the stratosphere 

can have significant downward influence on 

tropospheric circulation, is less well 

established. Sigmond et al. investigate the 

potential for such downward influence to alter 

current predictions of global warming. Comparing 

the predicted warming response in two general 

circulation models-one with a well-resolved 

stratosphere (high-top version) and one without a 

well-resolved stratosphere (low-top version)-they 

find significant differences. While similar 

results in the past have been taken as evidence 

that a well-resolved stratosphere is essential 

for modeling future climate projections, the 

authors question this conclusion. Instead, they 

show that further analysis demonstrates that the 

differing warming responses in the two models are 

not related to the differing model lid height, 

but are due to differing treatments of 

parameterized gravity waves, which have a large 

influence on the climatological winds in the 

lower stratosphere.

 

Title: Impact of the stratosphere on tropospheric climate change

 

Authors: Michael Sigmond and Paul J. Kushner: 

Department of Physics, University of Toronto, 

Toronto, Ontario, Canada;

 

John F. Scinocca: Canadian Centre for Climate 

Modelling and Analysis, Meteorological Service of 

Canada, Victoria, British Columbia, Canada;

 

Source: Geophysical Research Letters (GRL) paper 

10.1029/2008GL033573, 2008; 

http://dx.doi.org/10.1029/2008GL033573

 

7. How are human-made aerosols changing clouds?

 

Human-generated aerosol particles affect solar 

radiation by direct scattering and absorption, 

but also change cloud properties through 

particles acting as cloud condensation nuclei 

(CCN) and ice nuclei (IN), a pathway referred to 

as the “indirect aerosol effect.” This effect is 

likely the manifestation of two different 

aerosol-cloud interaction mechanisms. One 

encompasses aerosols’ effect on cloud water, 

specifically how a decrease in cloud particle 

size decreases precipitation efficiency, thereby 

increasing cloud lifetimes. Oreopoulos and 

Platnick study the other mechanism, called the 

Twomey effect, which involves the radiative 

effect of cloud microphysical changes only (no 

change in cloud water amount). Here the greater 

availability of CCN or IN yields clouds with more 

numerous but smaller cloud particles, and 

therefore larger optical thickness. The authors 

seek to quantify the spatial and temporal 

sensitivity of liquid clouds to the Twomey effect 

by studying data from NASA’s satellite-based 

Moderate Resolution Imaging Spectroradiometer for 

4 months in 2005. Through the global maps 

generated, they find that the detailed nature of 

cloud microphysical perturbations, as well as the 

unperturbed cloud properties, is important for 

determining the radiative forcing associated with 

the Twomey effect.

 

Title: The radiative susceptibility of cloudy 

atmospheres to droplet number perturbations, part 

2: Global analysis from MODIS

 

Authors: Lazaros Oreopoulos and Steven Platnick: 

Joint Center for Earth Systems Technology, 

University of Maryland Baltimore County, 

Baltimore, Maryland, U.S.A.; and Laboratory for 

Atmospheres, NASA Goddard Space Flight Center, 

Greenbelt, Maryland, U.S.A.

 

Source: Journal of Geophysical 

Research-Atmospheres (JGR-D) paper 

10.1029/2007JD009655, 2008; 

http://www.agu.org/journals/pip/jd/2007JD009655-pip.pdf 

This paper is “in press”.

 

8. Taking sharper look at key atmospheric region

 

The middle atmosphere is composed of the 

stratosphere and mesosphere and extends from 

about 12 to 90 kilometers (7.5 to 56 miles) in 

altitude. This region is important because it 

houses ozone, which shields the Earth from 

ultraviolet light, and gravity and planetary 

waves, which influence weather close to the 

Earth’s surface. Many atmospheric general 

circulation models (GCMs) currently used for 

climate studies do not have sufficiently high 

spatial resolution to resolve small-scale gravity 

waves. To understand the roles of such 

small-scale phenomena in the Earth’s climate, 

Watanabe et al. develop a new GCM that uses very 

high spatial resolution. This model has 

horizontal resolution of 0.5625 degrees in 

latitude and longitude, and covers a region that 

extends from the surface to a height of about 85 

km (53 mi) with uniform vertical resolution of 

300 meters (980 feet) throughout the middle 

atmosphere. This GCM successfully simulates the 

spontaneous generation of gravity waves by 

convection, topography, instability, and 

adjustment processes, as well as their 

propagation and dissipation, resulting in a 

realistic reproduction of general circulation in 

the midlatitude and polar stratosphere and 

mesosphere.

 

Title: General aspects of a T213L256 middle 

atmosphere general circulation model

 

Authors: Shingo Watanabe, Yoshio Kawatani, and 

Kazuyiki Miyazaki: Frontier Research Center for 

Global Change, Japan Agency for Marine-Earth 

Science and Technology, Yokohama, Japan;

 

Yoshihiro Tomikawa: National Institute of Polar Research, Tokyo, Japan;

 

Masaaki Takahashi: Frontier Research Center for 

Global Change, Japan Agency for Marine-Earth 

Science and Technology, Yokohama, Japan; Also at 

Center for Climate System Research, University of 

Tokyo, Kashiwa, Japan;

 

Kaoru Sato: Department of Earth and Planetary 

Science, Graduate School of Science, University 

of Tokyo, Tokyo, Japan.

 

Source: Journal of Geophysical 

Research-Atmospheres (JGR-D) paper 

10.1029/2008JD010026, 2008; 

http://dx.doi.org/10.1029/2008JD010026

 

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