Trends in MODIS and AERONET derived aerosol optical thickness over Northern Europe.

2019 | Tellus B Chem Phys Meteorol | 71 (1) (1-21)

Long-term Aqua and Terra MODIS (MODerate resolution Imaging Spectroradiometer) Collections 5.1 and 6.1 (c051 and c061, respectively) aerosol data have been combined with AERONET (AERosol RObotic NETwork) ground-based sun photometer observations to examine trends in aerosol optical thickness (AOT, at 550 nm) over Northern Europe for the months April to September. For the 1927 and 1559 daily coincident measurements that were obtained for c051 and c061, respectively, MODIS AOT varied by 86 and 90%, respectively, within the predicted uncertainty of one standard deviation of the retrieval over land (ΔAOT = ±0.05 ± 0.15·AOT). For the coastal AERONET site Gustav Dalen Tower (GDT), Sweden, larger deviations were found for MODIS c051 and c061 (79% and 75%, respectively, within predicted uncertainty). The Baltic Sea provides substantially better statistical representation of AOT than the surrounding land areas and therefore favours the investigations of trends in AOT over the region. Negative trends of 1.5% and 1.2% per year in AOT, based on daily averaging, were found for the southwestern Baltic Sea from MODIS c051 and c061, respectively. This is in line with a decrease of 1.2% per year in AOT at the AERONET station Hamburg. For the western Gotland Basin area, Sweden, negative trends of 1.5%, 1.1% and 1.6% per year in AOT have been found for MODIS c051, MODIS c061 and AERONET GDT, respectively. The strongest trend of –1.8% per year in AOT was found for AERONET Belsk, Poland, which can be compared to –1.5% per day obtained from MODIS c051 over central Poland. The trends in MODIS and AERONET AOT are nearly all statistically significant at the 95% confidence level. The strongest aerosol sources are suggested to be located southwest, south and southeast of the investigation area, although the highest prevalence of pollution events is associated with air mass transport from southwest.

Effect of Wind Speed on Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth over the North Pacific

Merkulova, L., Freud, E., Mårtensson, E. M., Nilsson, E.D., Glantz, P.
2018 | ATMOSPHERE | 9 (2) (60) (1-19)

The surface-wind speed influences on aerosol optical depth (AOD), derived from the
Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua daily observations over the central
North Pacific during the period 2003–2016, have been investigated in this study. The cloud coverage is
relatively low over the present investigation area compared to other marine areas, which favors AOD
derived from passive remote sensing from space. In this study, we have combined MODIS AOD with
2 m wind speed (U2m) on a satellite-pixel basis, which has been interpolated from National Centers for
Environmental Prediction (NCEP) reanalysis. In addition, daily averaged AOD derived from Aerosol
Robotic Network (AERONET) measurements in the free-troposphere at the Mauna Loa Observatory
(3397 m above sea level), Hawaii, was subtracted from the MODIS column AOD values. The latter
was to reduce the contribution of aerosols above the planetary boundary layer. This study shows
relatively strong power-law relationships between MODIS mean AOD and surface-wind speed for
marine background conditions in summer, fall and winter of the current period. However, previous
established relationships between AOD and surface-wind speed deviate substantially. Even so,
for similar marine conditions the present relationship agrees reasonable well with a power-law
relationship derived for north-east Atlantic conditions. The present MODIS retrievals of AOD in the
marine atmosphere agree reasonably well with ground-based remote sensing of AOD.

Spaceborne observations of low surface aerosol concentrations in the Stockholm region

2016 | TELLUS B | 68 (28951)

Aviation effects on already-existing cirrus clouds

M. Tesche; P. Achtert; P. Glantz; K. J. Noone
2016 | Nat. Commun. | 7 (12016)

Determining the effects of the formation of contrails within natural cirrus clouds has proven to be challenging. Quantifying any such effects is necessary if we are to properly account for the influence of aviation on climate. Here we quantify the effect of aircraft on the optical thickness of already-existing cirrus clouds by matching actual aircraft flight tracks to satellite lidar measurements. We show that there is a systematic, statistically significant increase in normalized cirrus cloud optical thickness inside mid-latitude flight tracks compared with adjacent areas immediately outside the tracks.

Remote sensing of aerosols in the Arctic for an evaluation of global climate model simulations

Glantz, P.; Bourassa, A.; Herber, A.; Iversen, T.; Karlsson, J.; Kirkevåg, A.; Maturilli; M.; Seland, O; Stebel, K.; Struthers, H.; Tesche, M.; Thomason, L.
2014 | J. Geophys. Res.-Atmos.

In this study Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua retrievals of aerosol
optical thickness (AOT) at 555 nm are compared to Sun photometer measurements from Svalbard for a
period of 9 years. For the 642 daily coincident measurements that were obtained, MODIS AOT generally
varies within the predicted uncertainty of the retrieval over ocean (ΔAOT = ±0.03 ± 0.05 · AOT). The results
from the remote sensing have been used to examine the accuracy in estimates of aerosol optical properties
in the Arctic, generated by global climate models and from in situ measurements at the Zeppelin station,
Svalbard. AOT simulated with the Norwegian Earth System Model/Community Atmosphere Model version 4 Oslo
global climate model does not reproduce the observed seasonal variability of the Arctic aerosol. The model
overestimates clear-sky AOT by nearly a factor of 2 for the background summer season, while tending to
underestimate the values in the spring season. Furthermore, large differences in all-sky AOT of up to 1 order of
magnitude are found for the CoupledModel Intercomparison Project phase 5 model ensemble for the spring and
summer seasons. Large differences between satellite/ground-based remote sensing of AOT and AOT estimated
from dry and humidified scattering coefficients are found for the subarctic marine boundary layer in summer.

A long-term satellite study of aerosol effects on convective clouds in Nordic background air

Sporre, M.; Swietlicki, E.; Glantz, P.; and Kulmala, M.
2014 | Atmos. Chem. Phys. | 14 (2203-2217)

Reconciling aerosol light extinction measurements from spaceborne lidar observations and in situ measurements in the Arctic

Tesche, M.; Zieger, P.; Rastak, N.; Charlson, R. J.; Glantz, P.; Tunved, P.; Hansson, H.-C
2014 | Atmos. Chem. Phys. | 14 (7869-7882)

In this study we investigate to what degree it is possible to reconcile continuously recorded particle light extinction coefficients derived from dry in situ measurements at Zeppelin station (78.92° N, 11.85° E; 475 m above sea level), Ny-Ålesund, Svalbard, that are recalculated to ambient relative humidity, as well as simultaneous ambient observations with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. To our knowledge, this represents the first study that compares spaceborne lidar measurements to optical aerosol properties from short-term in situ observations (averaged over 5 h) on a case-by-case basis. Finding suitable comparison cases requires an elaborate screening and matching of the CALIOP data with respect to the location of Zeppelin station as well as the selection of temporal and spatial averaging intervals for both the ground-based and spaceborne observations. Reliable reconciliation of these data cannot be achieved with the closest-approach method, which is often used in matching CALIOP observations to those taken at ground sites. This is due to the transport pathways of the air parcels that were sampled. The use of trajectories allowed us to establish a connection between spaceborne and ground-based observations for 57 individual overpasses out of a total of 2018 that occurred in our region of interest around Svalbard (0 to 25° E, 75 to 82° N) in the considered year of 2008. Matches could only be established during winter and spring, since the low aerosol load during summer in connection with the strong solar background and the high occurrence rate of clouds strongly influences the performance and reliability of CALIOP observations. Extinction coefficients in the range of 2 to 130 Mm−1 at 532 nm were found for successful matches with a difference of a factor of 1.47 (median value for a range from 0.26 to 11.2) between the findings of in situ and spaceborne observations (the latter being generally larger than the former). The remaining difference is likely to be due to the natural variability in aerosol concentration and ambient relative humidity, an insufficient representation of aerosol particle growth, or a misclassification of aerosol type (i.e., choice of lidar ratio) in the CALIPSO retrieval.

Aerosol indirect effects on continental low-level clouds over Sweden and Finland

Sporre, M. K.; Swietlicki, E.; Glantz, P; Kulmala, M.
2014 | Atmos. Chem. Phys. | 14 (12167-12179)

Climate-induced changes in sea salt aerosol number emissions: 1870 to 2100

Struthers, H., A.; Ekman, M. L.; Glantz, P.; Iversen, T.; Kirkevåg, A.; Seland, Ø.; Mårtensson, E. M.; Noone, K.; Nilsson, E. D.
2013 | J. Geophys. Res.-Atmos. | 118 (1-13)

Volcanic ash over Scandinavia originating from the Grímsvötn eruptions in May 2011.

Tesche, M.; Glantz, P.; Johansson, C.; Norman, M.G.; Hiebsch, A.; Seifert, A.; Ansmann, A.; Engelmann, R.; Althausen, D.
2012 | J. Geophys. Res.-Atmos. | 117

Assessment of two aerosol optical thickness retrieval algorithms applied to MODIS Aqua and Terra measurements in Europe

Glantz, P.; Tesche, M.
2012 | Atmos. Meas. Tech. | 5 (1727-1740)

The aim of the present study is to validate AOT
(aerosol optical thickness) and Angstrom exponent (alpha), obtained
from MODIS (MODerate resolution Imaging Spectroradiometer)
Aqua and Terra calibrated level 1 data (1 km
horizontal resolution at ground) with the SAER (Satellite
AErosol Retrieval) algorithm and with MODIS Collection
5 (c005) standard product retrievals (10 km horizontal resolution),
against AERONET (AErosol RObotic NETwork)
sun photometer observations over land surfaces in Europe.
An inter-comparison of AOT at 0.469 nm obtained with the
two algorithms has also been performed. The time periods
investigated were chosen to enable a validation of the findings
of the two algorithms for a maximal possible variation
in sun elevation. The satellite retrievals were also performed
with a significant variation in the satellite-viewing geometry,
since Aqua and Terra passed the investigation area twice
a day for several of the cases analyzed. The validation with
AERONET shows that the AOT at 0.469 and 0.555 nm obtained
with MODIS c005 is within the expected uncertainty
of one standard deviation of the MODIS c005 retrievals
(AOT =±0.05±0.15 ·AOT). The AOT at 0.443 nm retrieved
with SAER, but with a much finer spatial resolution,
also agreed reasonably well with AERONET measurements.
The majority of the SAER AOT values are within the MODIS
c005 expected uncertainty range, although somewhat larger
average absolute deviation occurs compared to the results obtained
with the MODIS c005 algorithm. The discrepancy between
AOT from SAER and AERONET is, however, substantially
larger for the wavelength 488 nm. This means that
the values are, to a larger extent, outside of the expected
MODIS uncertainty range. In addition, both satellite retrieval
algorithms are unable to estimate accurately, although
the MODIS c005 algorithm performs better. Based on the
inter-comparison of the SAER and MODIS c005 algorithms,
it was found that SAER on the whole is able to obtain results
within the expected uncertainty range of MODIS Aqua and
Terra observations.

A study of the indirect aerosol effect on subarctic marine liquid low-level clouds using MODIS cloud data and ground-based aerosol measurements

Sporre, M. K.; Glantz, P.; Tunved, P.; Swietlicki, E.; Kulmala, M.; Lihavainen, H.
2012 | Atmos. Res. | 116 (56-66)

Contact information

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Stockholm University
106 91 Stockholm

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