Seasonal and Diurnal Variations in Aerosol Concentration on Whistler Mountain: Boundary Layer Influence and Synoptic-Scale Controls

AbstractA mountain air chemistry observatory has been operational on the summit of Whistler Mountain in British Columbia, Canada, since 2002. A 1-yr dataset of condensation nuclei (CN) concentration from this site has been analyzed along with corresponding meteorological data to assess the frequency and patterns of influence from the planetary boundary layer (PBL). Characterization of air masses sampled from the site as either PBL influenced or representative of the free troposphere (FT) is important to subsequent analysis of the chemistry data. Median CN concentrations and seasonal trends were found to be comparable to other midlatitude mountain sites. Monthly median number concentrations ranged from 120 cm−3 in January to 1601 cm−3 in July. Using well-defined diurnal cycles in CN concentration as an indicator of air arriving from nearby valleys, PBL influence was found to occur on a majority of days during spring and summer and less frequently in late autumn and winter. Days with PBL influence were usually associated with synoptic-scale weather patterns that were conducive to convective mixing processes. Although more common in the warm season, vertical mixing capable of transporting valley air to the mountaintop also occurred in February during a period of high pressure aloft. In contrast, an August case study indicated that the more stable character of marine air masses can at times keep the PBL below the summit on summer days. Considerable variability in the synoptic-scale weather conditions at Whistler means that careful analysis of available datasets must be made to discriminate FT from PBL periods at the observatory.

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Synoptic-scale controls of fog and low-cloud variability in the Namib Desert

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-3415-2020 ◽

2020 ◽

Vol 20 (6) ◽

pp. 3415-3438 ◽

Cited By ~ 1

Author(s):

Hendrik Andersen ◽

Jan Cermak ◽

Julia Fuchs ◽

Peter Knippertz ◽

Marco Gaetani ◽

...

Keyword(s):

Boundary Layer ◽

Cloud Cover ◽

Large Scale ◽

Marine Boundary Layer ◽

Synoptic Scale ◽

Namib Desert ◽

Data Set ◽

Air Masses ◽

Low Cloud ◽

Low Cloud Cover

Abstract. Fog is a defining characteristic of the climate of the Namib Desert, and its water and nutrient input are important for local ecosystems. In part due to sparse observation data, the local mechanisms that lead to fog occurrence in the Namib are not yet fully understood, and to date, potential synoptic-scale controls have not been investigated. In this study, a recently established 14-year data set of satellite observations of fog and low clouds in the central Namib is analyzed in conjunction with reanalysis data in order to identify synoptic-scale patterns associated with fog and low-cloud variability in the central Namib during two seasons with different spatial fog occurrence patterns. It is found that during both seasons, mean sea level pressure and geopotential height at 500 hPa differ markedly between fog/low-cloud and clear days, with patterns indicating the presence of synoptic-scale disturbances on fog and low-cloud days. These regularly occurring disturbances increase the probability of fog and low-cloud occurrence in the central Namib in two main ways: (1) an anomalously dry free troposphere in the coastal region of the Namib leads to stronger longwave cooling of the marine boundary layer, increasing low-cloud cover, especially over the ocean where the anomaly is strongest; (2) local wind systems are modulated, leading to an onshore anomaly of marine boundary-layer air masses. This is consistent with air mass back trajectories and a principal component analysis of spatial wind patterns that point to advected marine boundary-layer air masses on fog and low-cloud days, whereas subsiding continental air masses dominate on clear days. Large-scale free-tropospheric moisture transport into southern Africa seems to be a key factor modulating the onshore advection of marine boundary-layer air masses during April, May, and June, as the associated increase in greenhouse gas warming and thus surface heating are observed to contribute to a continental heat low anomaly. A statistical model is trained to discriminate between fog/low-cloud and clear days based on information on large-scale dynamics. The model accurately predicts fog and low-cloud days, illustrating the importance of large-scale pressure modulation and advective processes. It can be concluded that regional fog in the Namib is predominantly of an advective nature and that fog and low-cloud cover is effectively maintained by increased cloud-top radiative cooling. Seasonally different manifestations of synoptic-scale disturbances act to modify its day-to-day variability and the balance of mechanisms leading to its formation and maintenance. The results are the basis for a new conceptual model of the synoptic-scale mechanisms that control fog and low-cloud variability in the Namib Desert and will guide future studies of coastal fog regimes.

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Synoptic-scale controls of fog and low clouds in the Namib Desert

10.5194/acp-2019-924 ◽

2019 ◽

Author(s):

Hendrik Andersen ◽

Jan Cermak ◽

Julia Fuchs ◽

Peter Knippertz ◽

Marco Gaetani ◽

...

Keyword(s):

Boundary Layer ◽

Large Scale ◽

Marine Boundary Layer ◽

Synoptic Scale ◽

Namib Desert ◽

Sea Level Pressure ◽

Mean Sea Level ◽

Air Masses ◽

Low Clouds ◽

Low Cloud

Abstract. Fog is a defining characteristic of the climate of the Namib Desert and its water and nutrient input are important for local ecosystems. In part due to sparse observation data, the local mechanisms that lead to fog occurrence in the Namib are not yet fully understood, and to date, potential synoptic-scale controls have not been investigated. In this study, a recently established 14-year data set of satellite observations of fog and low clouds in the central Namib is analyzed in conjunction with reanalysis data to identify typical synoptic-scale conditions associated with fog and low-cloud occurrence in the central Namib during two seasons that characterize seasonal fog variability. It is found that during both seasons, mean sea level pressure and geopotential height at 500 hPa differ significantly between fog/low-cloud and clear days, with patterns indicating seasonally different synoptic-scale disturbances on fog and low-cloud days: cut-off lows during September, October, and November, and breaking Rossby waves during April, May, and June. These regularly occurring disturbances increase the probability of fog and low-cloud occurrence in the central Namib in two main ways: 1) an anomalously dry free troposphere in the coastal region of the Namib leads to stronger longwave cooling, especially over the ocean, facilitating low-cloud formation, and 2) local wind systems are modulated, leading to an onshore anomaly of marine boundary-layer air masses. This is consistent with air mass backtrajectories and a principal component analysis of spatial wind patterns that point to advected marine boundary- layer air masses on fog and low-cloud days, whereas subsiding continental air masses dominate on clear days. Large-scale free-tropospheric moisture transport into southern Africa seems to be a key factor modulating the onshore advection of marine boundary-layer air masses during April, May, and June, as the associated increase in greenhouse gas warming and thus surface heating is observed to contribute to a continental heat low anomaly. A statistical model is trained to discriminate between fog/low-cloud and clear days based on large-scale mean sea level pressure fields. The model accurately predicts fog and low-cloud days, illustrating the importance of large-scale pressure modulation and advective processes. It can be concluded that Namib-region fog is predominantly of advective nature, but also facilitated by increased radiative cooling. Seasonally different manifestations of synoptic-scale disturbances act to modify its day-to-day variability and the balance of mechanisms leading to its formation. The results are the basis for a new conceptual model on the synoptic-scale mechanisms that control fog and low clouds in the Namib Desert, and will guide future studies of coastal fog regimes.

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Schneefernerhaus as a mountain research station for clouds and turbulence

Atmospheric Measurement Techniques ◽

10.5194/amt-8-3209-2015 ◽

2015 ◽

Vol 8 (8) ◽

pp. 3209-3218 ◽

Cited By ~ 8

Author(s):

S. Risius ◽

H. Xu ◽

F. Di Lorenzo ◽

H. Xi ◽

H. Siebert ◽

...

Keyword(s):

Velocity Structure ◽

Meteorological Data ◽

Weather Conditions ◽

Reynolds Numbers ◽

Research Station ◽

Synoptic Scale ◽

Third Order ◽

Air Turbulence ◽

Complementary Role ◽

East West

Abstract. Cloud measurements are usually carried out with airborne campaigns, which are expensive and are limited by temporal duration and weather conditions. Ground-based measurements at high-altitude research stations therefore play a complementary role in cloud study. Using the meteorological data (wind speed, direction, temperature, humidity, visibility, etc.) collected by the German Weather Service (DWD) from 2000 to 2012 and turbulence measurements recorded by multiple ultrasonic sensors (sampled at 10 Hz) in 2010, we show that the Umweltforschungsstation Schneefernerhaus (UFS) located just below the peak of Zugspitze in the German Alps, at a height of 2650 m, is a well-suited station for cloud–turbulence research. The wind at UFS is dominantly in the east–west direction and nearly horizontal. During the summertime (July and August) the UFS is immersed in warm clouds about 25 % of the time. The clouds are either from convection originating in the valley in the east, or associated with synoptic-scale weather systems typically advected from the west. Air turbulence, as measured from the second- and third-order velocity structure functions that exhibit well-developed inertial ranges, possesses Taylor microscale Reynolds numbers up to 104, with the most probable value at ~ 3000. In spite of the complex topography, the turbulence appears to be nearly as isotropic as many laboratory flows when evaluated on the "Lumley triangle".

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Ice Nucleating Particles in Southern Chile and their connection to clouds

10.5194/egusphere-egu21-7474 ◽

2021 ◽

Author(s):

Heike Wex ◽

Xianda Gong ◽

Boris Barja ◽

Patric Seifert ◽

Martin Radenz ◽

...

Keyword(s):

Warm Season ◽

Weather Conditions ◽

Chem Phys ◽

Cold Season ◽

Southern Chile ◽

Backscatter Coefficient ◽

Air Masses ◽

North West ◽

The North ◽

Almost All

Concentrations of atmospheric ice nucleating particles (INP) were obtained from weekly filter samples which were collected from May 2019 until March 2020 in southern Chile. Sampling took place at an altitude of 620m above sea level, on top of Cerro Mirador, a mountain directly to the west of Punta Arenas (53&#176;S, 71&#176;W). Additional aerosol properties such as particle number size distributions were measured as well. In parallel, ground-based remote sensing measurements with lidar and cloud radar were made in Punta Arenas.INP concentrations were obtained from washing atmospheric aerosol particles off from deployed polycarbonate filters and subsequent analysis of the samples on two different freezing arrays which were used and described by us earlier (e.g., in Gong et al., 2019 and Hartmann et al., 2020). INP concentrations could be obtained over a broad temperature range from above -5&#176;C down to -25&#176;C.INP concentrations were clearly higher than data obtained for the Southern Ocean region as reported in McCluskey et al. (2018) and Welti et al. (2020). Indeed, they were comparable to concentrations measured at Cape Verde (Gong et al., 2020). INP concentrations obtained during the warm season were spreading over ~ 2 orders of magnitude at any temperature. Data obtained for the cold season almost all were at the upper end of the observed INP concentration range, with only one weekly sample featuring low concentrations.Heating of the samples was also applied, and the heated samples had clearly lower INP concentrations across the examined temperatures, implying a biological fraction among the INP of ~ 80%. Therefore, local terrestrial sources may be the source of the observed INP.The assumption of local terrestrial sources is strengthened by a case study. For that, two subsequent samples obtained during the cold season were examined in more detail. These were the one sample with low INP concentrations which was obtained during the cold season during the week from August 14 to August 22, and the subsequent sample collected from August 22 to August 29, which was amongst the highest samples. Backward trajectories together with an analysis of Lidar data showed that the low INP concentrations were obtained for a time during which air masses predominantly came in from the south with little contact to land and for calm weather conditions. Conditions were not as stable during the following week which featured air masses mostly coming in from the north-west. The aerosol backscatter coefficient at the height level of the in-situ measurements was obtained from lidar observations for both weeks and shows about 50 % lower aerosol load for the first week, when INP concentrations were low.All of this hints to local terrestrial sources for the observed highly ice active biogenic INP.&#160;Literature:Gong et al. (2019), Atmos. Chem. Phys., 19, 10883-10900, doi:10.5194/acp-19-10883-2019.Gong et al. (2020), Atmos. Chem. Phys., 20, 1451-1468, doi:10.5194/acp-20-1451-2020.Hartmann et al. (2020), Geophys. Res. Lett., 47, doi:10.1029/2020GL087770.McCluskey et al. (2018), Geophys. Res. Lett., 45, doi:10.1029/2018gl079981.Welti et a. (2020), Atmos. Chem. Phys. 20, doi:10.5194/acp-2020-466.

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Studying boundary layer methane isotopy and vertical mixing processes at a rewetted peatland site using an unmanned aircraft system

Atmospheric Measurement Techniques ◽

10.5194/amt-13-1937-2020 ◽

2020 ◽

Vol 13 (4) ◽

pp. 1937-1952 ◽

Cited By ~ 1

Author(s):

Astrid Lampert ◽

Falk Pätzold ◽

Magnus O. Asmussen ◽

Lennart Lobitz ◽

Thomas Krüger ◽

...

Keyword(s):

Boundary Layer ◽

Vertical Distribution ◽

Isotopic Composition ◽

Water Samples ◽

Vertical Mixing ◽

Temperature Inversion ◽

Mixing Processes ◽

Air Masses ◽

The Vertical Distribution ◽

Different Altitudes

Abstract. The combination of two well-established methods, of quadrocopter-borne air sampling and methane isotopic analyses, is applied to determine the source process of methane at different altitudes and to study mixing processes. A proof-of-concept study was performed to demonstrate the capabilities of quadrocopter air sampling for subsequently analysing the methane isotopic composition δ13C in the laboratory. The advantage of the system compared to classical sampling on the ground and at tall towers is the flexibility concerning sampling location, and in particular the flexible choice of sampling altitude, allowing the study of the layering and mixing of air masses with potentially different spatial origin of air masses and methane. Boundary layer mixing processes and the methane isotopic composition were studied at Polder Zarnekow in Mecklenburg–West Pomerania in the north-east of Germany, which has become a strong source of biogenically produced methane after rewetting the drained and degraded peatland. Methane fluxes are measured continuously at the site. They show high emissions from May to September, and a strong diurnal variability. For two case studies on 23 May and 5 September 2018, vertical profiles of temperature and humidity were recorded up to an altitude of 650 and 1000 m, respectively, during the morning transition. Air samples were taken at different altitudes and analysed in the laboratory for methane isotopic composition. The values showed a different isotopic composition in the vertical distribution during stable conditions in the morning (delta values of −51.5 ‰ below the temperature inversion at an altitude of 150 m on 23 May 2018 and at an altitude of 50 m on 5 September 2018, delta values of −50.1 ‰ above). After the onset of turbulent mixing, the isotopic composition was the same throughout the vertical column with a mean delta value of −49.9 ± 0.45 ‰. The systematically more negative delta values occurred only as long as the nocturnal temperature inversion was present. During the September study, water samples were analysed as well for methane concentration and isotopic composition in order to provide a link between surface and atmosphere. The water samples reveal high variability on horizontal scales of a few tens of metres for this particular case. The airborne sampling system and consecutive analysis chain were shown to provide reliable and reproducible results for two samples obtained simultaneously. The method presents a powerful tool for distinguishing the source process of methane at different altitudes. The isotopic composition showed clearly depleted delta values directly above a biological methane source when vertical mixing was hampered by a temperature inversion, and different delta values above, where the air masses originate from a different footprint area. The vertical distribution of methane isotopic composition can serve as tracer for mixing processes of methane within the atmospheric boundary layer.

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Quantification of topographic venting of boundary layer air to the free troposphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-4-497-2004 ◽

2004 ◽

Vol 4 (2) ◽

pp. 497-509 ◽

Cited By ~ 141

Author(s):

S. Henne ◽

M. Furger ◽

S. Nyeki ◽

M. Steinbacher ◽

B. Neininger ◽

...

Keyword(s):

Boundary Layer ◽

Production Efficiency ◽

Weather Conditions ◽

Free Troposphere ◽

Fair Weather ◽

Air Mass ◽

Air Masses ◽

Mountainous Regions ◽

The Alps ◽

Alpine Valleys

Abstract. Net vertical air mass export by thermally driven flows from the atmospheric boundary layer (ABL) to the free troposphere (FT) above deep Alpine valleys was investigated. The vertical export of pollutants above mountainous terrain is presently poorly represented in global chemistry transport models (GCTMs) and needs to be quantified. Air mass budgets were calculated using aircraft observations obtained in deep Alpine valleys. The results show that on average 3 times the valley air mass is exported vertically per day under fair weather conditions. During daytime the type of valleys investigated in this study can act as an efficient "air pump" that transports pollutants upward. The slope wind system within the valley plays an important role in redistributing pollutants. Nitrogen oxide emissions in mountainous regions are efficiently injected into the FT. This could enhance their ozone (O3) production efficiency and thus influences tropospheric pollution budgets. Once lifted to the FT above the Alps pollutants are transported horizontally by the synoptic flow and are subject to European pollution export. Forward trajectory studies show that under fair weather conditions two major pathways for air masses above the Alps dominate. Air masses moving north are mixed throughout the whole tropospheric column and further transported eastward towards Asia. Air masses moving south descend within the subtropical high pressure system above the Mediterranean.

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Warunki biometeorologiczne Kłodzka i ich wpływ na klimatoterapię i turystykę

Prace Geograficzne ◽

10.4467/20833113pg.21.005.13430 ◽

2021 ◽

pp. 9-25

Author(s):

Bartłomiej Miszuk

Keyword(s):

Meteorological Data ◽

Warm Season ◽

Thermal Conditions ◽

Weather Conditions ◽

Human Organism ◽

Important Region ◽

Spring And Autumn Period ◽

Tourism Information ◽

Annual Scale ◽

The Impact

Biometeorological conditions of Kłodzko and their influence on climatotherapy and tourism The region of Kłodzko belongs to the most important tourist areas in the Lower Silesia. It is also a very important region in the context of health resorts. Because of significant impact of weather conditions on both tourism and health issues, a crucial aspect is to evaluate the influence of weather on human organism and various forms of climatotherapy, tourism and recreation. The goal of the paper was to evaluate the biometeorological conditions of Kłodzko, considering its bio-thermal conditions as well as the usefulness of weather for climatotherapy, tourism and recreation. The basis for the analysis was meteorological data for 1971–2015 from the IMGW-PIB station in Kłodzko. The evaluation of biometeorological conditions included the bio-thermal index of UTCI and the weather suitability index for tourism and recreation (WSI). The WSI is calculated on the basis of the MENEX model which enables an assessment of the human heat balance. The climate tourism information scheme (CTIS) was also considered. It enables an evaluation of recreational potential with a consideration of bio-thermal conditions and the impact of particular meteorological variables. Based on the mentioned methods, a structure of heat stress categories and the annual course of usefulness of weather for climatotherapy, tourism and recreation were presented. The results of the research showed that weather conditions related to no thermal stress prevail on an annual scale. As for the context of the impact of weather on tourism issues, the best conditions are observed in the warm season, especially in the spring and autumn period. The results of the study can be a source of information for tourists and bathers visiting the region. They can also be a basis for increasing the knowledge on biometeorological conditions of the Sudetes.

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Quantification of topographic venting of boundary layer air to the free troposphere

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-3-5205-2003 ◽

2003 ◽

Vol 3 (5) ◽

pp. 5205-5236 ◽

Cited By ~ 4

Author(s):

S. Henne ◽

M. Furger ◽

S. Nyeki ◽

M. Steinbacher ◽

B. Neininger ◽

...

Keyword(s):

Boundary Layer ◽

Weather Conditions ◽

Ozone Production ◽

Free Troposphere ◽

Fair Weather ◽

Air Mass ◽

Air Masses ◽

Mountainous Regions ◽

The Alps ◽

Alpine Valleys

Abstract. Net vertical air mass export by thermally driven f\\/lows from the atmospheric boundary layer (ABL) to the free troposphere (FT) above deep Alpine valleys was investigated. The vertical export of pollutants above mountainous terrain is presently poorly represented in global chemistry transport models (GCTMs) and needs to be quantified. Air mass budgets were calculated using aircraft observations obtained in deep Alpine valleys. The results show that on average 3 times the valley air mass is exported vertically per day under fair weather conditions. During daytime the type of valleys investigated in this study can act as an efficient "air pump" that transports pollutants upward. The slope wind system within the valley plays an important role in redistributing pollutants. Nitrogen oxide emissions in mountainous regions are efficiently injected into the FT. This enhances their ozone production efficiency and thus influences tropospheric pollution budgets. Once lifted to the FT above the Alps pollutants are transported horizontally by the synoptic flow and are subject to European pollution export. Forward trajectory studies show that under fair weather conditions two major pathways for air masses above the Alps dominate. Air masses moving north are mixed throughout the whole tropospheric column and further transported eastward towards Asia. Air masses moving south descend within the subtropical high pressure system above the Mediterranean.

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Spatiotemporal variation in urban overheating magnitude and its association with synoptic air-masses in a coastal city

Scientific Reports ◽

10.1038/s41598-021-86089-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Hassan Saeed Khan ◽

Mat Santamouris ◽

Pavlos Kassomenos ◽

Riccardo Paolini ◽

Peter Caccetta ◽

...

Keyword(s):

Weather Conditions ◽

Extreme Heat ◽

Daily Maximum ◽

Synoptic Scale ◽

Air Masses ◽

Coastal City ◽

Extreme Heat Events ◽

The Mean ◽

The Impact ◽

Heat Events

AbstractUrban overheating (UO) may interact with synoptic-scale weather conditions. The association between meteorological parameters and UO has already been a subject of considerable research, however, the impact of synoptic-scale weather conditions on UO magnitude, particularly in a coastal city that is also near the desert landmass (Sydney) has never been investigated before. The present research examines the influence of synoptic-scale weather conditions on UO magnitude in Sydney by utilizing the newly developed gridded weather typing classification (GWTC). The diurnal, and seasonal variations in suburban-urban temperature contrast (ΔT) in association with synoptic-scale weather conditions, and ΔT response to synoptic air-masses during extreme heat events are investigated in three zones of Sydney. Generally, an exacerbation in UO magnitude was reported at daytime over the years, whereas the nocturnal UO magnitude was alleviated over time. The humid warm (HW), and warm (W) air-masses were found primarily responsible for exacerbated daytime UO during extreme heat events and in all other seasons, raising the mean daily maximum ΔT to 8–10.5 °C in Western Sydney, and 5–6.5 °C in inner Sydney. The dry warm (DW), and W conditions were mainly responsible for urban cooling (UC) at nighttime, bringing down the mean daily minimum ΔT to − 7.5 to − 10 °C in Western Sydney, and − 6 to − 7.5 °C in inner Sydney. The appropriate mitigation technologies can be planned based on this study to alleviate the higher daytime temperatures in the Sydney suburbs.

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EXPERIMENTAL INVESTIGATION OF FLOW RESPONSE TO STATIONARY DISTURBANCE IN ROTATING-DISK FLOW

NED University Journal of Research ◽

10.35453/nedjr-ascn-2018-0047 ◽

2019 ◽

Vol XVI (2) ◽

pp. 13-22

Author(s):

Muhammad Ehtisham Siddiqui

Keyword(s):

Boundary Layer ◽

Boundary Layer Flow ◽

Three Dimensional ◽

Rotating Disk ◽

Careful Analysis ◽

Laboratory Frame ◽

Transition To Turbulence ◽

Turbulent Regime ◽

Mean Velocity ◽

Layer Flow

Three-dimensional boundary-layer flow is well known for its abrupt and sharp transition from laminar to turbulent regime. The presented study is a first attempt to achieve the target of delaying the natural transition to turbulence. The behaviour of two different shaped and sized stationary disturbances (in the laboratory frame) on the rotating-disk boundary layer flow is investigated. These disturbances are placed at dimensionless radial location (Rf = 340) which lies within the convectively unstable zone over a rotating-disk. Mean velocity profiles were measured using constant-temperature hot-wire anemometry. By careful analysis of experimental data, the instability of these disturbance wakes and its estimated orientation within the boundary-layer were investigated.

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