scholarly journals Spring snow albedo feedback over northern Eurasia: Comparing in situ measurements with reanalysis products

2018 ◽  
Vol 12 (6) ◽  
pp. 1887-1898 ◽  
Author(s):  
Martin Wegmann ◽  
Emanuel Dutra ◽  
Hans-Werner Jacobi ◽  
Olga Zolina
Keyword(s):  
State Of The Art ◽  
Northern Eurasia ◽  
Albedo Feedback ◽  
Snow Albedo ◽  
Station Data ◽  
In Situ Observations ◽  
Improved Performance ◽  
Set Up ◽  
Modern Era

Abstract. This study uses daily observations and modern reanalyses in order to evaluate reanalysis products over northern Eurasia regarding the spring snow albedo feedback (SAF) during the period from 2000 to 2013. We used the state-of-the-art reanalyses from ERA-Interim/Land and the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) as well as an experimental set-up of ERA-Interim/Land with prescribed short grass as land cover to enhance the comparability with the station data while underlining the caveats of comparing in situ observations with gridded data. Snow depth statistics derived from daily station data are well reproduced in all three reanalyses. However day-to-day albedo variability is notably higher at the stations than for any reanalysis product. The ERA-Interim grass set-up shows improved performance when representing albedo variability and generates comparable estimates for the snow albedo in spring. We find that modern reanalyses show a physically consistent representation of SAF, with realistic spatial patterns and area-averaged sensitivity estimates. However, station-based SAF values are significantly higher than in the reanalyses, which is mostly driven by the stronger contrast between snow and snow-free albedo. Switching to grass-only vegetation in ERA-Interim/Land increases the SAF values up to the level of station-based estimates. We found no significant trend in the examined 14-year time series of SAF, but interannual changes of about 0.5 % K−1 in both station-based and reanalysis estimates were derived. This interannual variability is primarily dominated by the variability in the snowmelt sensitivity, which is correctly captured in reanalysis products. Although modern reanalyses perform well for snow variables, efforts should be made to improve the representation of dynamic albedo changes.

scholarly journals Spring snow albedo feedback over Northern Eurasia: Comparing in-situ measurements with reanalysis products

2017 ◽  
Author(s):  
Martin Wegmann ◽  
Emanuel Dutra ◽  
Hans-Werner Jacobi ◽  
Olga Zolina
Keyword(s):  
State Of The Art ◽  
Northern Eurasia ◽  
Snow Melt ◽  
Albedo Feedback ◽  
Snow Albedo ◽  
Station Data ◽  
Annual Changes ◽  
Improved Performance ◽  
Modern Era

Abstract. This study uses daily observations and modern reanalyses in order to evaluate reanalysis products over Northern Eurasia regarding the spring snow albedo feedback (SAF) during the period from 2000 to 2013. We used the state of the art reanalyses ERA-Interim land and the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA2) as well as an experimental setup of ERA-Interim land with prescribed short grass as land cover to enhance the comparibility with the station data. While snow depth statistics derived from daily station data are well reproduced in all three reanalyses, the day-to-day variability of the albedo is notably higher at stations compared to any reanalysis product. The ERA-Interim grass setup shows an improved performance in representing albedo variability and generates comparable estimates for the snow albedo in spring. We find that modern reanalyses show a physically consistent representation of SAF, with realistic spatial patterns and area-averaged sensitivity estimates. However, station-based SAF values are significantly higher than in the reanalyses, which is mostly driven by the stronger contrast beween snow and snow-free albedo. Switching to grass-only vegetation in ERA-Interim land increases the SAF values up to the level of station-based estimates. We found no significant trend in the examined 14-year timeseries of SAF, but inter- annual changes of about 0.5 % K−1 in both station-based and reanalysis estimates were derived. This inter-annual variability is primarily dominated by the variability in the snow melt sensitivity, which is correctly captured in reanalysis products. Although modern reanalyses perform well for snow variables, efforts should be made to improve the representation of dynamic albedo changes.

Solar Orbiter observations of magnetic Kelvin-Helmholtz waves in the solar wind

2021 ◽  
Author(s):  
Rungployphan Kieokaew ◽  
Benoit Lavraud ◽  
David Ruffolo ◽  
William Matthaeus ◽  
Yan Yang ◽  
...  
Keyword(s):  
Solar Wind ◽  
Heliospheric Current Sheet ◽  
Shear Instability ◽  
Slow Solar Wind ◽  
Flow Shear ◽  
In Situ Observations ◽  
Set Up ◽  
Nonlinear Shear ◽  
Wind Source

<p>The Kelvin-Helmholtz instability (KHI) is a nonlinear shear-driven instability that develops at the interfaces between shear flows in plasmas. KHI is ubiquitous in plasmas and has been observed in situ at planetary interfaces and at the boundaries of coronal mass ejections in remote-sensing observations. KHI is also expected to develop at flow shear interfaces in the solar wind, but while it was hypothesized to play an important role in the mixing of plasmas and exciting solar wind fluctuations, its direct observation in the solar wind was still lacking. We report first in-situ observations of ongoing KHI in the solar wind using Solar Orbiter during its cruise phase. The KHI is found in a shear layer in the slow solar wind near the Heliospheric Current Sheet. We find that the observed conditions satisfy the KHI onset criterion from linear theory and the steepening of the shear boundary layer is consistent with the development of KH vortices. We further investigate the solar wind source of this event to understand the conditions that support KH growth. In addition, we set up a local MHD simulation using the empirical values to reproduce the observed KHI. This observed KHI in the solar wind provides robust evidence that shear instability develops in the solar wind, with obvious implications in the driving of solar wind fluctuations and turbulence. The reasons for the lack of previous such measurements are also discussed.</p>

scholarly journals Spatial and seasonal distribution of Arctic aerosols observed by CALIOP (2006–2012)

2013 ◽  
Vol 13 (2) ◽  
pp. 4863-4915 ◽  
Author(s):  
M. Di Pierro ◽  
L. Jaeglé ◽  
E. W. Eloranta ◽  
S. Sharma
Keyword(s):  
Volcanic Eruptions ◽  
The Arctic ◽  
Northern Eurasia ◽  
Orthogonal Polarization ◽  
Aerosol Extinction ◽  
Free Troposphere ◽  
Atlantic Sector ◽  
Arctic Oscillation Index ◽  
In Situ Observations

Abstract. We use retrievals of aerosol extinction from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the CALIPSO satellite to examine the vertical, horizontal and temporal variability of tropospheric Arctic aerosols during 2006–2012. We develop an empirical method that takes into account the difference in sensitivity between daytime and nighttime retrievals over the Arctic. Comparisons of the retrieved aerosol extinction to in situ measurements at Barrow (Alaska) and Alert (Canada) show that CALIOP reproduces the observed seasonal cycle and magnitude of surface aerosols to within 25%. In the free troposphere, we find that daytime CALIOP retrievals will only detect the strongest aerosol haze events as demonstrated by a comparison to aircraft measurements obtained during NASA's ARCTAS mission during April 2008. This leads to a systematic underestimate of the column aerosol optical depth by a factor of 2–10. However, when the CALIOP sensitivity threshold is applied to aircraft observations, we find that CALIOP reproduces in situ observations to within 20% and captures the vertical profile of extinction over the Alaskan Arctic. Comparisons with the ground-based HSRL Lidar at Eureka, Canada, show that CALIOP and HSRL capture the evolution of the aerosol backscatter vertical distribution from winter to spring, but a quantitative comparison is inconclusive as the retrieved HSRL backscatter appears to overestimate in situ observations factor of 2 at all altitudes. In the High Arctic (> 70° N) near the surface (< 2 km), CALIOP aerosol extinctions reach a maximum in December-March (10–20 Mm−1), followed by a sharp decline and a minimum in May–September (1–4 Mm−1), thus providing the first Pan-Arctic view of Arctic Haze seasonality. The European and Asian Arctic sectors display the highest wintertime extinctions, while the Atlantic sector is the cleanest. Over the Low Arctic (60–70° N) near the surface, CALIOP extinctions reach a maximum over land in summer due to boreal forest fires. During summer, we find that smoke aerosols reach higher altitudes (up to 4 km) over Eastern Siberia and North America than over Northern Eurasia, where it remains mostly confined below 2 km. In the free troposphere, the extinction maximum over the Arctic occurs in March–April at 2–5 km altitude and April–May at 5–8 km. This is consistent with transport from the mid-latitudes associated with the annual maximum in cyclonic activity and blocking patterns in the Northern Hemisphere. A strong gradient in aerosol extinction is observed between 60° N and 70° N in the summer. This is likely due to efficient stratocumulus wet scavenging at high latitudes combined with the poleward retreat of the polar front. Interannual variability in the middle and upper troposphere is associated with biomass burning events (high extinctions observed by CALIOP in spring 2008 and summer 2010) and volcanic eruptions (Kasatochi in August 2008 and Sarychev in June 2009). CALIOP displays below-average extinctions observed from August 2009 through May 2010, which appear to be linked with a strongly negative Arctic Oscillation index.

In Situ Observations and Measurements of Mechanically Induced Grain Boundary Migration in a Scanning Electron Microscope

2012 ◽  
Vol 715-716 ◽  
pp. 819-824 ◽  
Author(s):  
Tatiana Gorkaya ◽  
Thomas Burlet ◽  
Dmitri A. Molodov ◽  
Günter Gottstein
Keyword(s):  
Shear Stress ◽  
Grain Boundary ◽  
Elevated Temperatures ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Orientation Contrast ◽  
In Situ Observations ◽  
Set Up ◽  
Scanning Electron

A novel set-up developed to continuously observe and measure stress driven grain boundary migration is presented. A commercially available tensile/compression SEM unit was utilized for in-situ observations of mechanically loaded samples at elevated temperatures up to 850°C by recording orientation contrast images of bicrystal surfaces. Two sample holders for application of a shear stress to the boundary in bicrystals of different geometry were designed and fabricated. The results of first measurements are presented.

scholarly journals Reverse engineering field-derived vertical distribution profiles to infer larval swimming behaviors

2019 ◽  
pp. 201900238 ◽  
Author(s):  
M. K. James ◽  
J. A. Polton ◽  
A. R. Brereton ◽  
K. L. Howell ◽  
W. A. M. Nimmo-Smith ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
State Of The Art ◽  
Distribution Patterns ◽  
Environmental Cues ◽  
Biophysical Models ◽  
Marine Larvae ◽  
In Situ Observations ◽  
The Vertical Distribution ◽  
Larval Swimming

Biophysical models are well-used tools for predicting the dispersal of marine larvae. Larval behavior has been shown to influence dispersal, but how to incorporate behavior effectively within dispersal models remains a challenge. Mechanisms of behavior are often derived from laboratory-based studies and therefore, may not reflect behavior in situ. Here, using state-of-the-art models, we explore the movements that larvae must undertake to achieve the vertical distribution patterns observed in nature. Results suggest that behaviors are not consistent with those described under the tidally synchronized vertical migration (TVM) hypothesis. Instead, we show (i) a need for swimming speed and direction to vary over the tidal cycle and (ii) that, in some instances, larval swimming cannot explain observed vertical patterns. We argue that current methods of behavioral parameterization are limited in their capacity to replicate in situ observations of vertical distribution, which may cause dispersal error to propagate over time, due to advective differences over depth and demonstrate an alternative to laboratory-based behavioral parameterization that encompasses the range of environmental cues that may be acting on planktic organisms.

In-Situ Observations on Crack Propagation Along Polymer/Glass Interfaces.

2005 ◽  
Vol 875 ◽  
Author(s):  
W.P. Vellinga ◽  
R. Timmerman ◽  
R. van Tijum ◽  
J.Th.M. De Hosson
Keyword(s):  
Double Cantilever Beam ◽  
Optical Microscope ◽  
Lateral Movement ◽  
Forward Movement ◽  
Optical Microscope Image ◽  
Glass Interface ◽  
In Situ Observations ◽  
Set Up ◽  
Processing Techniques

AbstractThe propagation of crack fronts along a PET-glass interface is illustrated. The experimental set-up consists of an Asymmetric Double Cantilever Beam in an optical microscope. Image processing techniques used to isolate the crack fronts are discussed in some detail. The fronts are found to propagate inhomogeneously in space and time, in forward bursts that spread laterally along the front for some distance. In some cases the forward movement of a crack can be almost entirely due to the lateral movement of forward steps (analogous to “kinks”) along the crack front.

scholarly journals Spatial and seasonal distribution of Arctic aerosols observed by the CALIOP satellite instrument (2006–2012)

2013 ◽  
Vol 13 (14) ◽  
pp. 7075-7095 ◽  
Author(s):  
M. Di Pierro ◽  
L. Jaeglé ◽  
E. W. Eloranta ◽  
S. Sharma
Keyword(s):  
Volcanic Eruptions ◽  
High Spectral Resolution ◽  
The Arctic ◽  
Northern Eurasia ◽  
Aerosol Extinction ◽  
Free Troposphere ◽  
Atlantic Sector ◽  
Arctic Oscillation Index ◽  
In Situ Observations

Abstract. We use retrievals of aerosol extinction from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard the CALIPSO satellite to examine the vertical, horizontal and temporal variability of tropospheric Arctic aerosols during the period 2006–2012. We develop an empirical method that takes into account the difference in sensitivity between daytime and nighttime retrievals over the Arctic. Comparisons of the retrieved aerosol extinction to in situ measurements at Barrow (Alaska) and Alert (Canada) show that CALIOP reproduces the observed seasonal cycle and magnitude of surface aerosols to within 25 %. In the free troposphere, we find that daytime CALIOP retrievals will only detect the strongest aerosol haze events, as demonstrated by a comparison to aircraft measurements obtained during NASA's ARCTAS mission during April 2008. This leads to a systematic underestimate of the column aerosol optical depth by a factor of 2–10. However, when the CALIOP sensitivity threshold is applied to aircraft observations, we find that CALIOP reproduces in situ observations to within 20% and captures the vertical profile of extinction over the Alaskan Arctic. Comparisons with the ground-based high spectral resolution lidar (HSRL) at Eureka, Canada, show that CALIOP and HSRL capture the evolution of the aerosol backscatter vertical distribution from winter to spring, but a quantitative comparison is inconclusive as the retrieved HSRL backscatter appears to overestimate in situ observations by a factor of 2 at all altitudes. In the High Arctic (>70° N) near the surface (<2 km), CALIOP aerosol extinctions reach a maximum in December–March (10–20 Mm−1), followed by a sharp decline and a minimum in May–September (1–4 Mm−1), thus providing the first pan-Arctic view of Arctic haze seasonality. The European and Asian Arctic sectors display the highest wintertime extinctions, while the Atlantic sector is the cleanest. Over the Low Arctic (60–70° N) near the surface, CALIOP extinctions reach a maximum over land in summer due to boreal forest fires. During summer, we find that smoke aerosols reach higher altitudes (up to 4 km) over eastern Siberia and North America than over northern Eurasia, where they remain mostly confined below 2 km. In the free troposphere, the extinction maximum over the Arctic occurs in March–April at 2–5 km altitude and April–May at 5–8 km. This is consistent with transport from the midlatitudes associated with the annual maximum in cyclonic activity and blocking patterns in the Northern Hemisphere. A strong gradient in aerosol extinction is observed between 60° N and 70° N in the summer. This is likely due to efficient stratocumulus wet scavenging at high latitudes combined with the poleward retreat of the polar front. Interannual variability in the middle and upper troposphere is associated with biomass burning events (high extinctions observed by CALIOP in spring 2008 and summer 2010) and volcanic eruptions (Kasatochi in August 2008 and Sarychev in June 2009). CALIOP displays below-average extinctions observed from August 2009 through May 2010, which appear to be linked with a strongly negative Arctic Oscillation index.

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