scholarly journals Contrasting ice formation in Arctic clouds: surface-coupled vs. surface-decoupled clouds

2021 ◽  
Vol 21 (13) ◽  
pp. 10357-10374
Author(s):  
Hannes J. Griesche ◽  
Kevin Ohneiser ◽  
Patric Seifert ◽  
Martin Radenz ◽  
Ronny Engelmann ◽  
...  
Keyword(s):  
Potential Temperature ◽  
The Arctic ◽  
Radiosonde Data ◽  
Ice Formation ◽  
Cloud Base ◽  
Data Set ◽  
Thermodynamic Structure ◽  
Cloud Radar ◽  
Lower Magnitude ◽  
Surface Coupling

Abstract. In the Arctic summer of 2017 (1 June to 16 July) measurements with the OCEANET-Atmosphere facility were performed during the Polarstern cruise PS106. OCEANET comprises amongst other instruments the multiwavelength polarization lidar PollyXT_OCEANET and for PS106 was complemented with a vertically pointed 35 GHz cloud radar. In the scope of the presented study, the influence of cloud height and surface coupling on the probability of clouds to contain and form ice is investigated. Polarimetric lidar data were used for the detection of the cloud base and the identification of the thermodynamic phase. Both radar and lidar were used to detect cloud top. Radiosonde data were used to derive the thermodynamic structure of the atmosphere and the clouds. The analyzed data set shows a significant impact of the surface-coupling state on the probability of ice formation. Surface-coupled clouds were identified by a quasi-constant potential temperature profile from the surface up to liquid layer base. Within the same minimum cloud temperature range, ice-containing clouds have been observed more frequently than surface-decoupled clouds by a factor of up to 6 (temperature intervals between −7.5 and −5 ∘C, 164 vs. 27 analyzed intervals of 30 min). The frequency of occurrence of surface-coupled ice-containing clouds was found to be 2–3 times higher (e.g., 82 % vs. 35 % between −7.5 and −5 ∘C). These findings provide evidence that above −10 ∘C heterogeneous ice formation in Arctic mixed-phase clouds occurs by a factor of 2–6 more often when the cloud layer is coupled to the surface. In turn, for minimum cloud temperatures below −15 ∘C, the frequency of ice-containing clouds for coupled and decoupled conditions approached the respective curve for the central European site of Leipzig, Germany (51∘ N, 12∘ E). This corroborates the hypothesis that the free-tropospheric ice nucleating particle (INP) reservoir over the Arctic is controlled by continental aerosol. Two sensitivity studies, also using the cloud radar for detection of ice particles and applying a modified coupling state detection, both confirmed the findings, albeit with a lower magnitude. Possible explanations for the observations are discussed by considering recent in situ measurements of INP in the Arctic, of which much higher concentrations were found in the surface-coupled atmosphere in close vicinity to the ice shore.

scholarly journals Contrasting ice formation in Arctic clouds: surface coupled vs decoupled clouds

2020 ◽  
Author(s):  
Hannes J. Griesche ◽  
Kevin Ohneiser ◽  
Patric Seifert ◽  
Albert Ansmann ◽  
Ronny Engelmann
Keyword(s):  
Potential Temperature ◽  
Cloud Layer ◽  
The Arctic ◽  
Ice Formation ◽  
Marine Aerosols ◽  
Data Set ◽  
Arctic Clouds ◽  
Constant Potential ◽  
Ice Multiplication ◽  
Surface Coupling

Abstract. In the Arctic summer of 2017 (June, 1st to July, 16th) measurements with the multiwavelength polarization lidar PollyXT-OCEANET, 35-GHz cloud radar of the OCEANET platform, and radiosonde measurements were conducted during cruise PS106 of the research vessel Polarstern around Svalbard. In the scope of the presented study, the influence of cloud height and surface coupling on the probability of clouds to contain and form ice is investigated. The analyzed data set shows a significant impact of the surface-coupling state on the probability of ice formation. Surface-coupled clouds, identified by a quasi-constant potential temperature profile from the surface up to liquid layer base, in the same cloud-top temperature range contain ice more frequent than decoupled clouds by a factor of up to 5 for cloud-top intervals between −7.5 and −5 °C (169 vs. 31 profiles). These findings provide evidence that heterogeneous ice formation in Arctic mixed-phase clouds occurs by a factor of 2–5 more likely when the cloud layer is coupled to the surface. In turn, for cloud-top temperatures below −15 °C, the frequency of ice-containing cloud profiles for coupled and decoupled conditions approached the respective curve for the Central-European site of Leipzig, Germany (51° N, 12° E). This provides further evidence that the free-tropospheric ice nucleating particles (INP) reservoir over the Arctic is controlled by continental aerosol. One possible explanation for the observation is that turbulent mixing of the air below surface-coupled clouds allows ice particles, acting as seeds for ice multiplication, or marine aerosols, acting as INP, to be transported into the cloud layer more efficiently than in the case of decoupled conditions. This hypothesis is corroborated by recent in-situ measurements of INP in the Arctic, of which much higher concentrations were found in the surface-coupled atmosphere in close vicinity to the ice shore. Using lidar measurements we also found evidence for enhanced INP number concentrations (INPC) within surface-coupled cloud-free air masses. The INPC have been estimated based on particle backscatter profiles, published freezing spectra of biogenic INP and existing parameterizations.

scholarly journals Assessing the vertical structure of Arctic aerosols using balloon-borne measurements

2021 ◽  
Vol 21 (3) ◽  
pp. 1737-1757
Author(s):  
Jessie M. Creamean ◽  
Gijs de Boer ◽  
Hagen Telg ◽  
Fan Mei ◽  
Darielle Dexheimer ◽  
...  
Keyword(s):  
Vertical Structure ◽  
Potential Temperature ◽  
Atmospheric Stability ◽  
Surface Energy Budget ◽  
Radiative Properties ◽  
Cloud Formation ◽  
The Arctic ◽  
Cloud Base ◽  
Cloud Environment ◽  
Near Surface

Abstract. The rapidly warming Arctic is sensitive to perturbations in the surface energy budget, which can be caused by clouds and aerosols. However, the interactions between clouds and aerosols are poorly quantified in the Arctic, in part due to (1) limited observations of vertical structure of aerosols relative to clouds and (2) ground-based observations often being inadequate for assessing aerosol impacts on cloud formation in the characteristically stratified Arctic atmosphere. Here, we present a novel evaluation of Arctic aerosol vertical distributions using almost 3 years' worth of tethered balloon system (TBS) measurements spanning multiple seasons. The TBS was deployed at the U.S. Department of Energy Atmospheric Radiation Measurement Program's facility at Oliktok Point, Alaska. Aerosols were examined in tandem with atmospheric stability and ground-based remote sensing of cloud macrophysical properties to specifically address the representativeness of near-surface aerosols to those at cloud base. Based on a statistical analysis of the TBS profiles, ground-based aerosol number concentrations were unequal to those at cloud base 86 % of the time. Intermittent aerosol layers were observed 63 % of the time due to poorly mixed below-cloud environments, mostly found in the spring, causing a decoupling of the surface from the cloud layer. A uniform distribution of aerosol below cloud was observed only 14 % of the time due to a well-mixed below-cloud environment, mostly during the fall. The equivalent potential temperature profiles of the below-cloud environment reflected the aerosol profile 89 % of the time, whereby a mixed or stratified below-cloud environment was observed during a uniform or layered aerosol profile, respectively. In general, a combination of aerosol sources, thermodynamic structure, and wet removal processes from clouds and precipitation likely played a key role in establishing observed aerosol vertical structures. Results such as these could be used to improve future parameterizations of aerosols and their impacts on Arctic cloud formation and radiative properties.

scholarly journals Research on Retrieval of Atmospheric Temperature and Humidity Profiles from combined Ground-based Microwave Radiometer and Cloud Radar Observations

2016 ◽  
Author(s):  
Yunfei Che ◽  
Shuqing Ma ◽  
Fenghua Xing ◽  
Siteng Li ◽  
Yaru Dai
Keyword(s):  
Neural Network ◽  
Microwave Radiometer ◽  
Radiosonde Data ◽  
Training Dataset ◽  
Cloud Base ◽  
Optimal Method ◽  
Cloud Radar ◽  
Cloud Thickness ◽  
Humidity Profiles ◽  
Cloud Base Height

Abstract. This paper focuses on the retrieval of temperature and relative humidity profiles through combining ground-based microwave radiometer observations with those of millimeter-wavelength cloud radar. The cloud-base height and cloud thickness from the cloud radar were added into the atmospheric profile retrieval process, and a back propagation neural network method was used as the retrieval tool. Because substantial data are required to train a neural network, and microwave radiometer data are insufficient for this purpose, eight years of radiosonde data from Beijing were used as a database. The model MonoRTM was used to calculate the brightness temperature of the same channel as the microwave radiometer. Part of the cloud-base height and cloud thickness in the training dataset was also estimated using the radiosonde data. The accuracy of the results was analyzed by comparing with L-band sounding radar data, and quantified using the mean bias, root-mean-square error and correlation coefficient. The statistical results showed that inversion with cloud information was the optimal method. Compared with the inversion profiles without cloud information, the RMSE values after adding the cloud information were to a varying degree reduced for the vast majority of height layers. These reductions were particularly clear in layers with cloud present. The maximum reduction of RMSE for temperature was 2.2 K, and for the humidity profile was 16 %.

scholarly journals Assessing the vertical structure of Arctic aerosols using tethered-balloon-borne measurements

2020 ◽  
Author(s):  
Jessie M. Creamean ◽  
Gijs de Boer ◽  
Hagen Telg ◽  
Fan Mei ◽  
Darielle Dexheimer ◽  
...  
Keyword(s):  
Vertical Structure ◽  
Potential Temperature ◽  
Surface Energy Budget ◽  
Radiative Properties ◽  
Cloud Formation ◽  
The Arctic ◽  
Cloud Base ◽  
Cloud Environment ◽  
Tethered Balloon ◽  
Near Surface

Abstract. The rapidly-warming Arctic is sensitive to perturbations in the surface energy budget, which can be caused by clouds and aerosols. However, the interactions between clouds and aerosols are poorly quantified in the Arctic, in part due to: (1) limited observations of vertical structure of aerosols relative to clouds and (2) ground-based observations often being inadequate for assessing aerosol impacts on cloud formation in the characteristically stratified Arctic atmosphere. Here, we present a novel evaluation of Arctic aerosol vertical distributions using almost 3 years' worth of tethered balloon system (TBS) measurements spanning multiple seasons. The TBS was deployed at the U.S. Department of Energy Atmospheric Radiation Measurement Program's facility at Oliktok Point, Alaska. Aerosols were examined in tandem with atmospheric stability and ground-based remote sensing of cloud macrophysical properties to specifically address the representativeness of near-surface aerosols to those at cloud base. Based on a statistical analysis of the TBS profiles, ground-based aerosol number concentrations were unequal to those at cloud base 86 % of the time. Intermittent aerosol layers were observed 63 % of the time due to poorly mixed below-cloud environments, mostly in the spring, causing a decoupling of the surface from the cloud layer. A uniform distribution of aerosol below cloud was observed only 14 % of the time due to a well-mixed below-cloud environment, mostly during the fall. The equivalent potential temperature profiles of the below-cloud environment reflected the aerosol profile 89 % of the time whereby a mixed or stratified below-cloud environment was observed during a uniform or layered aerosol profile, respectively. In general, a combination of aerosol sources, thermodynamic structure, and wet removal processes from clouds and precipitation likely played a key role in establishing observed aerosol vertical structure. Results such as these could be used to improve future parameterizations of aerosols and their impacts on Arctic cloud formation and radiative properties.

scholarly journals GPS radio occultation with CHAMP and SAC-C: global monitoring of thermal tropopause parameters

2005 ◽  
Vol 5 (6) ◽  
pp. 1473-1488 ◽  
Author(s):  
T. Schmidt ◽  
S. Heise ◽  
J. Wickert ◽  
G. Beyerle ◽  
C. Reigber
Keyword(s):  
Standard Deviation ◽  
Potential Temperature ◽  
Weather Forecast ◽  
Lapse Rate ◽  
Radiosonde Data ◽  
Temperature Profiles ◽  
Quasi Biennial Oscillation ◽  
Data Set ◽  
Medium Range Weather Forecast ◽  
Satellite Missions

Abstract. In this study the global lapse-rate tropopause (LRT) pressure, temperature, potential temperature, and sharpness are discussed based on Global Positioning System (GPS) radio occultations (RO) from the German CHAMP (CHAllenging Minisatellite Payload) and the U.S.-Argentinian SAC-C (Satelite de Aplicaciones Cientificas-C) satellite missions. Results with respect to seasonal variations are compared with operational radiosonde data and ECMWF (European Centre for Medium-Range Weather Forecast) operational analyses. Results on the tropical quasi-biennial oscillation (QBO) are updated from an earlier study. CHAMP RO data are available continuously since May 2001 with on average 150 high resolution temperature profiles per day. SAC-C data are available for several periods in 2001 and 2002. In this study temperature data from CHAMP for the period May 2001-December 2004 and SAC-C data from August 2001-October 2001 and March 2002-November 2002 were used, respectively. The bias between GPS RO temperature profiles and radiosonde data was found to be less than 1.5K between 300 and 10hPa with a standard deviation of 2-3K. Between 200-20hPa the bias is even less than 0.5K (2K standard deviation). The mean deviations based on 167699 comparisons between CHAMP/SAC-C and ECMWF LRT parameters are (-2.1±37.1)hPa for pressure and (0.1±4.2)K for temperature. Comparisons of LRT pressure and temperature between CHAMP and nearby radiosondes (13230) resulted in (5.8±19.8)hPa and (-0.1±3.3)K, respectively. The comparisons between CHAMP/SAC-C and ECMWF show on average the largest differences in the vicinity of the jet streams with up to 700m in LRT altitude and 3K in LRT temperature, respectively. The CHAMP mission generates the first long-term RO data set. Other satellite missions will follow (GRACE, COSMIC, MetOp, TerraSAR-X, EQUARS) generating together some thousand temperature profiles daily.

scholarly journals 30 years of upper air soundings on board of R/V <i>POLARSTERN</i>

2016 ◽  
Vol 8 (1) ◽  
pp. 213-220 ◽  
Author(s):  
Amelie Driemel ◽  
Bernd Loose ◽  
Hannes Grobe ◽  
Rainer Sieger ◽  
Gert König-Langlo
Keyword(s):  
Austral Summer ◽  
Weather Forecast ◽  
The Arctic ◽  
Radiosonde Data ◽  
Data Sets ◽  
Polar Regions ◽  
Data Set ◽  
Northern Summer ◽  
Special Value ◽  
Remote Sensing Systems

Abstract. The research vessel and supply icebreaker POLARSTERN is the flagship of the Alfred-Wegener-Institut in Bremerhaven (Germany) and one of the infrastructural pillars of German Antarctic research. Since its commissioning in 1982, POLARSTERN has conducted 30 campaigns to Antarctica (157 legs, mostly austral summer), and 29 to the Arctic (94 legs, northern summer). Usually, POLARSTERN is more than 300 days per year in operation and crosses the Atlantic Ocean in a meridional section twice a year. The first radiosonde on POLARSTERN was released on the 29 December 1982, 2 days after POLARSTERN started on its maiden voyage to the Antarctic. And these daily soundings have continued up to the present. Due to the fact that POLARSTERN has reliably and regularly been providing upper air observations from data sparse regions (oceans and polar regions), the radiosonde data are of special value for researchers and weather forecast services alike. In the course of 30 years (29 December 1982 to 25 November 2012) a total of 12 378 radiosonde balloons were started on POLARSTERN. All radiosonde data can now be found at König-Langlo (2015, doi:10.1594/PANGAEA.810000). Each data set contains the directly measured parameters air temperature, relative humidity and air pressure, and the derived altitude, wind direction and wind speed. 432 data sets additionally contain ozone measurements.Although more sophisticated techniques (meteorological satellites, aircraft observation, remote-sensing systems, etc.) have nowadays become increasingly important, the high vertical resolution and quality of radiosonde data remains paramount for weather forecasts and modelling approaches.

scholarly journals The prevalence of precipitation from polar supercooled clouds

2021 ◽  
Vol 21 (5) ◽  
pp. 3949-3971
Author(s):  
Israel Silber ◽  
Ann M. Fridlind ◽  
Johannes Verlinde ◽  
Andrew S. Ackerman ◽  
Grégory V. Cesana ◽  
...  
Keyword(s):  
Large Scale ◽  
Microwave Radiometer ◽  
Detection Sensitivity ◽  
Cloud Formation ◽  
The Arctic ◽  
Ice Formation ◽  
Cloud Base ◽  
Energy Budgets ◽  
Polar Regions ◽  
Scale Models

Abstract. Supercooled clouds substantially impact polar surface energy budgets, but large-scale models often underestimate their occurrence, which motivates accurately establishing metrics of basic processes. An analysis of long-term measurements at Utqiaġvik, Alaska, and McMurdo Station, Antarctica, combines lidar-validated use of soundings to identify supercooled cloud layers and colocated ground-based profiling radar measurements to quantify cloud base precipitation. We find that more than 85 % (75 %) of sampled supercooled layers are precipitating over the Arctic (Antarctic) site, with more than 75 % (50 %) precipitating continuously to the surface. Such high frequencies can be reconciled with substantially lesser spaceborne estimates by considering differences in radar hydrometeor detection sensitivity. While ice precipitation into supercooled clouds from aloft is common, we also find that the great majority of supercooled cloud layers without ice falling into them are themselves continuously generating precipitation. Such sustained primary ice formation is consistent with continuous activation of immersion-mode ice-nucleating particles (INPs), suggesting that supercooled cloud formation is a principal gateway to ice formation at temperatures greater than ∼-38 ∘C over polar regions. The prevalence of weak precipitation fluxes is also consistent with supercooled cloud longevity and with well-observed and widely simulated case studies. An analysis of colocated microwave radiometer retrievals suggests that weak precipitation fluxes can be nonetheless consequential to moisture budgets for supercooled clouds owing to small liquid water paths. The results here also demonstrate that the observed abundance of mixed-phase clouds can vary substantially with instrument sensitivity and methodology. Finally, we suggest that these ground-based precipitation rate statistics offer valuable guidance for improving the representation of polar cloud processes in large-scale models.

scholarly journals On the Relationship between Thermodynamic Structure and Cloud Top, and Its Climate Significance in the Arctic

2012 ◽  
Vol 25 (7) ◽  
pp. 2374-2393 ◽  
Author(s):  
Joseph Sedlar ◽  
Matthew D. Shupe ◽  
Michael Tjernström
Keyword(s):  
Radiative Forcing ◽  
Thermodynamic Characteristics ◽  
Longwave Radiation ◽  
Specific Humidity ◽  
The Arctic ◽  
Cloud Base ◽  
Simple Liquid ◽  
Central Arctic Ocean ◽  
Thermodynamic Structure ◽  
Temperature Inversions

Abstract Cloud and thermodynamic characteristics from three Arctic observation sites are investigated to understand the collocation between low-level clouds and temperature inversions. A regime where cloud top was 100–200 m above the inversion base [cloud inside inversion (CII)] was frequently observed at central Arctic Ocean sites, while observations from Barrow, Alaska, indicate that cloud tops were more frequently constrained to inversion base height [cloud capped by inversion (CCI)]. Cloud base and top heights were lower, and temperature inversions were also stronger and deeper, during CII cases. Both cloud regimes were often decoupled from the surface except for CCI over Barrow. In-cloud lapse rates differ and suggest increased cloud-mixing potential for CII cases. Specific humidity inversions were collocated with temperature inversions for more than 60% of the CCI and more than 85% of the CII regimes. Horizontal advection of heat and moisture is hypothesized as an important process controlling thermodynamic structure and efficiency of cloud-generated motions. The portion of CII clouds above the inversion contains cloud radar signatures consistent with cloud droplets. The authors test the longwave radiative impact of cloud liquid above the inversion through hypothetical liquid water distributions. Optically thin CII clouds alter the effective cloud emission temperature and can lead to an increase in surface flux on the order of 1.5 W m−2 relative to the same cloud but whose top does not extend above the inversion base. The top of atmosphere impact is even larger, increasing outgoing longwave radiation up to 10 W m−2. These results suggest a potentially significant longwave radiative forcing via simple liquid redistributions for a distinctly dominant cloud regime over sea ice.

scholarly journals Radiative and dynamical contributions to past and future Arctic stratospheric temperature trends

2014 ◽  
Vol 14 (3) ◽  
pp. 1679-1688 ◽  
Author(s):  
P. Bohlinger ◽  
B.-M. Sinnhuber ◽  
R. Ruhnke ◽  
O. Kirner
Keyword(s):  
Atmospheric Chemistry ◽  
Planetary Wave ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Wave Activity ◽  
The Arctic ◽  
Radiosonde Data ◽  
Data Set ◽  
The Past ◽  
Stratospheric Temperature

Abstract. Arctic stratospheric ozone depletion is closely linked to the occurrence of low stratospheric temperatures. There are indications that cold winters in the Arctic stratosphere have been getting colder, raising the question if and to what extent a cooling of the Arctic stratosphere may continue into the future. We use meteorological reanalyses from the European Centre for Medium Range Weather Forecasts (ECMWF) ERA-Interim and NASA's Modern-Era Retrospective-Analysis for Research and Applications (MERRA) for the past 32 yr together with calculations of the chemistry-climate model (CCM) ECHAM/MESSy Atmospheric Chemistry (EMAC) and models from the Chemistry-Climate Model Validation (CCMVal) project to infer radiative and dynamical contributions to long-term Arctic stratospheric temperature changes. For the past three decades the reanalyses show a warming trend in winter and cooling trend in spring and summer, which agree well with trends from the Radiosonde Innovation Composite Homogenization (RICH) adjusted radiosonde data set. Changes in winter and spring are caused by a corresponding change of planetary wave activity with increases in winter and decreases in spring. During winter the increase of planetary wave activity is counteracted by a residual radiatively induced cooling. Stratospheric radiatively induced cooling is detected throughout all seasons, being highly significant in spring and summer. This means that for a given dynamical situation, according to ERA-Interim the annual mean temperature of the Arctic lower stratosphere has been cooling by −0.41 ± 0.11 K decade−1 at 50 hPa over the past 32 yr. Calculations with state-of-the-art models from CCMVal and the EMAC model qualitatively reproduce the radiatively induced cooling for the past decades, but underestimate the amount of radiatively induced cooling deduced from reanalyses. There are indications that this discrepancy could be partly related to a possible underestimation of past Arctic ozone trends in the models. The models project a continued cooling of the Arctic stratosphere over the coming decades (2001–2049) that is for the annual mean about 40% less than the modeled cooling for the past, due to the reduction of ozone depleting substances and the resulting ozone recovery. This projected cooling in turn could offset between 15 and 40% of the Arctic ozone recovery.

scholarly journals Historic temperature observations on Nordaustlandet, north-east Svalbard

2021 ◽  
Vol 40 ◽  
Author(s):  
Björn-Martin Sinnhuber
Keyword(s):  
Meteorological Data ◽  
High Arctic ◽  
The Arctic ◽  
Radiosonde Data ◽  
Data Set ◽  
North East ◽  
Temperature Observations ◽  
Temperature Time ◽  
Continuous Temperature

Long-term meteorological data for the Arctic are sparse. One of the longest quasi-continuous temperature time series in the High Arctic is the extended Svalbard Airport series, providing daily temperature data from 1898 until the present. Here, I derive an adjustment to historic temperature observations on the island of Nordaustlandet, north-east Svalbard, in order to link these to the extended Svalbard Airport series. This includes the Haudegen observations at Rijpfjorden during 1944/45 and a previously unrecognized data set obtained by the Norwegian hunters and trappers Gunnar Knoph and Henry Rudi during their wintering at Rijpfjorden in 1934/35. The adjustment is based on data from an automatic weather station at Rijpfjorden during 2014–16 and verified with other independent historic temperature observations on Nordaustlandet. An analysis of the Haudegen radiosonde data indicates that the surface temperature observations at Rijpfjorden are generally well correlated with the free tropospheric temperatures at 850 hPa, but occasionally show the occurrence of boundary-layer inversions during winter, where local temperatures fall substantially below what is expected from the regression. The adjusted historic observations from Nordaustlandet can, therefore, be used to fill remaining gaps in the extended Svalbard Airport series.

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