The concept of cloud radiative forcing (CRF) is commonly applied to quantify the impact of clouds on the surface radiative energy budget (REB). In
the Arctic, specific radiative interactions between ...microphysical and macrophysical properties of clouds and the surface strongly modify the warming
or cooling effect of clouds, complicating the estimate of CRF obtained from observations or models. Clouds tend to increase the broadband surface
albedo over snow or sea ice surfaces compared to cloud-free conditions. However, this effect is not adequately considered in the derivation of CRF
in the Arctic so far. Therefore, we have quantified the effects caused by surface-albedo–cloud interactions over highly reflective snow or sea ice
surfaces on the CRF using radiative transfer simulations and below-cloud airborne observations above the heterogeneous springtime marginal sea ice
zone (MIZ) during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign. The impact of a modified surface
albedo in the presence of clouds, as compared to cloud-free conditions, and its dependence on cloud optical thickness is found to be relevant for
the estimation of the shortwave CRF. A method is proposed to consider this surface albedo effect on CRF estimates by continuously retrieving the cloud-free
surface albedo from observations under cloudy conditions, using an available snow and ice albedo parameterization. Using ACLOUD data
reveals that the estimated average shortwave cooling by clouds almost doubles over snow- and ice-covered surfaces (−62 W m−2 instead of
−32 W m−2), if surface-albedo–cloud interactions are considered. As a result, the observed total (shortwave plus longwave) CRF shifted
from a warming effect to an almost neutral one. Concerning the seasonal cycle of the surface albedo, it is demonstrated that this effect enhances
shortwave cooling in periods when snow dominates the surface and potentially weakens the cooling by optically thin clouds during the summertime
melting season. These findings suggest that the surface-albedo–cloud interaction should be considered in global climate models and in long-term
studies to obtain a realistic estimate of the shortwave CRF to quantify the role of clouds in Arctic amplification.
Induction chemotherapy followed by primary radiotherapy in responders is considered an alternative to surgery for advanced cancer of the larynx and hypopharynx (LHC). Comparison of therapeutic ...approaches is challenging and must respect oncological and functional outcome as well as quality of life during and after treatment. One aspect of primary radiochemotherapy is the option of salvage surgery in case of residual tumor. The outcome after salvage surgery following new organ-preserving strategies has to be examined. All patients undergoing induction chemotherapy with paclitaxel and cisplatin followed by radiotherapy from 01/96 to 07/05 were included. Salvage surgery was performed either for local recurrence or suspected persistent nodal disease. Complete tumor removal, perioperative morbidity, and overall survival were analyzed in a retrospective study. 28 out of 134 patients underwent salvage surgery after primary treatment with induction chemotherapy and radiotherapy for advanced LHC. 15 patients had laryngectomy (LE) with neck dissection (ND), while 1 patient had lasersurgical partial laryngeal resection with ND for local recurrences. Twelve patients had salvage ND for suspicion of persistent lymph node metastases. 73% of LE patients had major postoperative problems such as pharyngocutaneous fistulas. In 56% of the cases, tumor removal turned out to be microscopically incomplete. Eight out of 12 patients who underwent salvage ND because of suspicious lymph nodes (66%) were free of vital tumor. When metastatic disease was present in the neck (4/12), recurrences occurred in 75% during postoperative follow-up. Only 2 out of 20 patients undergoing surgery for histologically proven recurrence after radiochemotherapy (10%) are actually tumor-free and alive after a mean observation time of 43.9 months. Salvage surgery for local recurrence is associated with high morbidity and poor oncological and functional outcome. ND for suspicious persistent nodal disease after radiochemotherapy can be an over-treatment. In our patients, it was burdened with cervical recurrences and distant metastases in presence of histologically confirmed lymph node metastases. In the light of our results, unfavourable outcome after salvage surgery must be pointed out when initially informing patients about different therapeutic options for advanced LHC.
Clouds play a potentially important role in Arctic climate change but are poorly represented in current atmospheric models across scales. To
improve the representation of Arctic clouds in models, it ...is necessary to compare models to observations to consequently reduce this
uncertainty. This study compares aircraft observations from the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD)
campaign around Svalbard, Norway, in May–June 2017 and simulations using the ICON (ICOsahedral Non-hydrostatic) model in its numerical weather
prediction (NWP) setup at 1.2 km horizontal resolution. By comparing measurements of solar and terrestrial irradiances during ACLOUD
flights to the respective properties in ICON, we showed that the model systematically overestimates the transmissivity of the mostly liquid clouds
during the campaign. This model bias is traced back to the way cloud condensation nuclei (CCN) get activated into cloud droplets in the two-moment
bulk microphysical scheme used in this study. This process is parameterized as a function of grid-scale vertical velocity in the microphysical scheme
used, but in-cloud turbulence cannot be sufficiently resolved at 1.2 km horizontal resolution in Arctic clouds. By parameterizing
subgrid-scale vertical motion as a function of turbulent kinetic energy, we are able to achieve a more realistic CCN activation into cloud
droplets. Additionally, we showed that by scaling the presently used CCN activation profile, the hydrometeor number concentration could be modified
to be in better agreement with ACLOUD observations in our revised CCN activation parameterization. This consequently results in an improved
representation of cloud optical properties in our ICON simulations.
Low-level airborne observations of the Arctic surface radiative energy budget are discussed. We focus on the terrestrial part of the budget, quantified by the thermal-infrared net irradiance (TNI). ...The data were collected in cloudy and cloud-free conditions over and in the vicinity of the marginal sea ice zone (MIZ) close to Svalbard during two aircraft campaigns conducted in the spring of 2019 and in the early summer of 2017. The measurements, complemented by ground-based observations available from the literature and radiative transfer simulations, are used to evaluate the influence of surface type (sea ice, open ocean, MIZ), seasonal characteristics, and synoptically driven meridional air mass transports into and out of the Arctic on the near-surface TNI. The analysis reveals a typical four-mode structure of the frequency distribution of the TNI as a function of surface albedo, the sea ice fraction, and surface brightness temperature. Two modes prevail over sea ice and another two over open ocean, each representing cloud-free and cloudy radiative states. Characteristic shifts and modifications of the TNI modes during the transition from winter to spring and early summer conditions are discussed. Furthermore, the influence of warm air intrusions (WAIs) and marine cold-air outbreaks (MCAOs) on the near-surface downward thermal-infrared irradiances and the TNI is highlighted for several case studies. It is concluded that during WAIs the surface warming depends on cloud properties and evolution. Lifted clouds embedded in warmer air masses over a colder sea ice surface, decoupled from the ground by a surface-based temperature inversion, have the potential to warm the surface more strongly than near-surface fog or thin low-level boundary layer clouds because of a higher cloud base temperature. For MCAOs it is found that the thermodynamic profile of the southward-moving air mass adapts only slowly to the warmer ocean surface.
For large-scale and long-term Arctic climate simulations appropriate parameterization of the surface albedo is required.
Therefore, the sea ice surface (SIS) albedo parameterization of the coupled ...regional climate model HIRHAM–NAOSIM was examined against broadband surface albedo measurements performed during the joint ACLOUD (Arctic CLoud Observations Using airborne measurements during polar Day) and PASCAL (Physical feedbacks of Arctic boundary layer, Sea ice, Cloud and AerosoL) campaigns, which were performed in May–June 2017 north of Svalbard. The SIS albedo parameterization was tested using measured quantities of the prognostic variables surface temperature and snow depth to calculate the surface albedo and the individual fractions of the ice surface subtypes (snow-covered ice, bare ice, and melt ponds) derived from digital camera images taken on board the Polar 5 and 6 aircraft.
The selected low-altitude (less than 100 m) flight sections of overall 12 flights were performed over surfaces dominated by snow-covered ice. It was found that the range of parameterized SIS albedo for individual days is smaller than that of the measurements. This was attributed to the biased functional dependence of the SIS albedo parameterization on temperature. Furthermore, a time-variable bias was observed with higher values compared to the modeled SIS albedo (0.88 compared to 0.84 for 29 May 2017) in the beginning of the campaign, and an opposite trend towards the end of the campaign (0.67 versus 0.83 for 25 June 2017). Furthermore, the surface type fraction parameterization was tested against the camera image product, which revealed an agreement within 1 %.
An adjustment of the variables, defining the parameterized SIS albedo, and additionally accounting for the cloud cover could reduce the root-mean-squared error from 0.14 to 0.04 for cloud free/broken cloud situations and from 0.06 to 0.05 for overcast conditions.
Arctic summer sea ice experiences rapid changes in its sea-ice concentration, surface albedo, and the melt pond fraction. This affects the energy balance of the region and demands an accurate ...knowledge of those surface characteristics in climate models. In this paper, the broadband albedo (300–3000 nm) of Arctic sea ice is derived from MEdium Resolution Imaging Spectrometer (MERIS) optical swath data by transforming the spectral albedo as an output from the Melt Pond Detector (MPD) algorithm with a newly developed spectral-to-broadband conversion (STBC). The new STBC replaces the previously applied spectral averaging method to provide a more accurate broadband albedo product, which approaches the accuracy of 0.02–0.05 required in climate simulations and allows a direct comparison to broadband albedo values from climate models. The STBC is derived empirically from spectral and broadband albedo measurements over landfast ice. It is validated on a variety of simultaneous spectral and broadband field measurements over Arctic sea ice, is compared to existing conversion techniques, and performs better than the currently published algorithms. The root-mean-square deviation (RMSD) between broadband albedo that was measured and converted by the STBC is 0.02. Other conversion techniques, the spectral averaging method and the linear combination of albedo values from four MERIS channels, result in higher RMSDs of 0.09 and 0.05, respectively. The improved MERIS-derived broadband albedo values are validated with airborne measurements. Results show a smaller RMSD of 0.04 for landfast ice than the RMSD of 0.07 for drifting ice. The MERIS-derived broadband albedo is compared to broadband albedo from ERA5 reanalysis to examine the albedo parameterization used in ERA5. Both albedo products agree over large scales and in temporal patterns. However, consistency in point-to-point comparison is rather poor, with differences up to 0.20, correlations between 0.69 and 0.79, and RMSDs in excess of 0.10. Differences in sea-ice concentration and cloud-masking uncertainties play a role, but most discrepancies can be attributed to climatological sea-ice albedo values used in ERA5. They are not adequate and need revising, in order to better simulate surface heat fluxes in the Arctic. The advantage of the resulting broadband albedo data set from MERIS over other published data sets is the accompanied data set of available melt pond fraction. Melt ponds are the main reason for the sea-ice albedo change in summer but are currently not represented in climate models and atmospheric reanalysis. Additional information about melt evolution, together with accurate albedo retrievals, can aid the challenging representation of sea-ice optical properties in those models in summer.
The Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign was carried out north-west of Svalbard (Norway) between 23 May and 6 June 2017. The objective of ACLOUD ...was to study Arctic boundary layer and mid-level clouds and their role in Arctic amplification. Two research aircraft (Polar 5 and 6) jointly performed 22 research flights over the transition zone between open ocean and closed sea ice. Both aircraft were equipped with identical instrumentation for measurements of basic meteorological parameters, as well as for turbulent and radiative energy fluxes. In addition, on Polar 5 active and passive remote sensing instruments were installed, while Polar 6 operated in situ instruments to characterize cloud and aerosol particles as well as trace gases. A detailed overview of the specifications, data processing, and data quality is provided here. It is shown that the scientific analysis of the ACLOUD data benefits from the coordinated operation of both aircraft. By combining the cloud remote sensing techniques operated on Polar 5, the synergy of multi-instrument cloud retrieval is illustrated. The remote sensing methods were validated using truly collocated in situ and remote sensing observations. The data of identical instruments operated on both aircraft were merged to extend the spatial coverage of mean atmospheric quantities and turbulent and radiative flux measurement. Therefore, the data set of the ACLOUD campaign provides comprehensive in situ and remote sensing observations characterizing the cloudy Arctic atmosphere. All processed, calibrated, and validated data are published in the World Data Center PANGAEA as instrument-separated data subsets (Ehrlich et al., 2019b, https://doi.org/10.1594/PANGAEA.902603).
Journal Editor Marcia Lacey asked Joseph Stapf, Director of Utilities for the City of Wyoming, Michigan, to talk about his experiences with outsourcing and to share his knowledge of how to get the ...best results when using this tool.
Risk Management Planning Oxenford, Moderated by Jeff
Journal - American Water Works Association,
August 1998, 1998-08-00, 19980801, Letnik:
90, Številka:
8
Journal Article
Recenzirano
Water utilities must submit risk management plans for handling hazardous chemicals by June 21, 1999.
Ship-based cloud remote sensing observations made onboard R/V Meteor
during the ElUcidating the RolE of Cloud-Circulation Coupling in ClimAte, EUREC4A,
campaign are presented and used to calculate ...cloud droplet number concentrations. The calculation is based on cloud liquid water path LWP and droplet effective radius reff retrieved from spectral measurements of transmitted solar radiance. It is shown that measurement uncertainties and retrieval assumptions impact the accuracy of the results. A case study indicates that the retrieval of LWP and reff is most affected by 3D-radiative effects in case of shallow cumulus and drizzle, which violates the adiabatic theory and plan-parallel geometry on which the radiative transfer simulations of the retrieval are based. Depending on the cloud thickness, the retrieval of reff might suffers from ambiguity.
These retrieval uncertainties and their implications on the estimated cloud droplet
number concentration are investigated by a sensitivity study. The analysis showed that
most of the uncertainty is introduced by reff, whereas LWP contributes significantly to
the uncertainty only for thin clouds. Therefore, it is concluded that only selected cloud
cases, which do not violate the retrieval assumption, such as stratiform cloud layers, are suited to apply the retrieval approach in further studies.
Fernerkundungsmessungen von Wolken auf dem Forschungsschiff
R/V Meteor während der ElUcidating the RolE of Cloud-Circulation Coupling in
ClimAte, EUREC4A, Kampagnewerden vorgestellt und zur Berechnung der Tröpfchenanzahlkonzentration verwendet. Die Berechnung basiert auf Messungen des Flüssigwasserpfads LWP und dem effektiven Tröpfchenradius reff, welche aus spektralen Messungen der transmittierten solaren Strahldichte abgeleitet wurden. Es wird gezeigt, dass Messunsicherheiten und Annahmen bei der Ableitung der Wolkeneigenschaften die Genauigkeit der Ergebnisse beeinflussen. Eine Fallstudie zeigt, dass die Ableitung von LWP und reff am stärksten durch 3-dimensionale Strahlungseffekte von flachen Cumuli und Nieselregen beeinflusst wird. Beides wiederspricht den Idealisierungen von adiabatischen Wolken und einer planparallelen Geometrie, auf denen die Strahlungstransfersimulationen des Verfahrens beruhen. Abhängig von der Wolkendicke kann die Ableitung von reff zusätzlich durch Mehrdeutigkeiten beeinflusst sein.
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