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Airborne lidar study of convective boundary layer development over pre-alpine terrain
J. Aerosol Sci. Vol.30,Suppl.i, pp.$209-$210,1999 O 1999PublishedbyElsevierScienceLtd.Allfightsreserved Printedin GreatBritain
Pergamon
0021-8502/99/$ - see frontmatter
A I R B O R N E L I D A R STUDY OF C O N V E C T I V E BOUNDARY L A Y E R DEVELOPMENT OVER PRE-ALPINE TERRAIN S. Nyeki ~'2, S. de Wekker 3, D. Steyn3, M. Kossmann 4, M. Kalberer 1, I. Colbeck 2 and U. Baltensperger I l Paul Scherrer Institute, 5232 Villigen PSI, Switzerland 2 Institute for Environ. Res., University of Essex, Colchester, Essex, England 3 Dept. of Geography, University of British Columbia, Vancouver, Canada n Dept. of Geography, University of Canterbury, Christchurch, New Zealand
KEYWORDS CBL, lidar, pre-alpine terrain, European Alps The structure of the convective boundary layer (CBL) and the exchange of CBL air masses with the free troposphere (FT) over complex mountainous terrain, is at present poorly understood. More recent studies have begun to use airborne lidar to observe CBL development over large spatial scales, such as the Pacific 93 campaign in the Lower Fraser Valley near Vancouver (e.g. Hoff e t a l . , 1997). The forthcoming Intensive Observation Period of the Mesoscale Alpine Project (MAP) over the European Alps in September 1999 will allow a comprehensive study to be conducted within the framework of an extensive airborne and ground-based measurement programme. In preparation for MAP, preliminary investigations were performed during an airbome campaign over the Jungfraujoch 46.-~ high-alpine research station (JFJ; 3454 m asl) Switzerland on 30 July 1997, in which 46. aerosol (Nyeki e t a l . , 1999) and lidar measurements were conducted. The present work focuses on development of the CBL 46. structure over the following regions shown in Fig. 1: a) pre-alpine terrain (500 - 2000 m asl) 46. in the Emmental region upwind of the JFJ, and b) over Lake Brienz (564 m asl). An extensive anticyclone was located over 46. central Europe, resulting in clear conditions with a light wind from the northwest (305 46.~ 315°). Radiosonde profiles for a pre-alpine location (Payeme, CH; 490 m asl, 85 km distant, WNW) confirmed a stable 46.: atmospheric stratification in the free troposphere ( d O / d z ~ 5.5 K km l for 3 - 5 km 46.1 7.60 7.70 7.80 7.90 8.00 8.10 8.20 8.30 8.40 asl). Moming (0100 LST; = UTC + 1) and afternoon (1300 LST) profiles indicated a Fig. 1. Map of the JFJ region indicating the subsidence inversion at about 2650 m asl. A nominal flight pattern of lidar transects at 8.0 downward-looking aerosol lidar (~ = 532 nm) km asl. Topographical elevation intervals at 1.0 aboard the German Aerospace Establishment km, darkest interval 3.0 - 4.0 km asl. For details (DLR) Falcon 20 jet aircraft was used to monitor atmospheric structure below 8 km of transects see text.
$209
$210
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Abstracts of the 1999 EuropeanAerosolConference
,
,
7.70
7.75
7,80
,t
7,70
7.75
7.80
7.85
7.85 Longitude
7,90
7,95
7.90
7.95
46.50
8.00
,~4o
46.60
46.~L~ti~¢ N46.~o
46.70
46.80
46.70
E
Fig. 2. Comparison of O1 transects during: a) the morning (0735 LST) and b) afternoon (1350 LST) flight. Lake Brienz lies east of 7.88°E.
Fig. 3. Comparison of P5 transects during: a) the morning (0815 LST) and b) afternoon LST) flight. Lake Brienz lies at 46.70°N [with the Emmental region north of this point.
1(1425
asl. Multiple passes were flown within a 40 x 75 km horizontal domain centred over the JFJ, where the five main transects were near-parallel to the wind and orthogonal to the regional alpine divide (see Fig. 1). Lidar results from identical morning and afternoon flight patterns over Lake Brienz (transect O1) are shown in Fig. 2a-b, respectively, and over a pre/high-alpine transect (transect P5) in Fig. 3a-b. Morning convective activity in the Emmental region (north of 46.70°N in Fig. 3a-b) is already seen to have begun and results in some cloud formation above south-facing slopes by the afternoon. Enhanced backscatter over Lake Brienz is most probably due to the hygroscopic growth of aerosols, rather than due to anthropogenic pollution, in this instance. A number of interesting features are evident. Convective cells are apparent in irregularities at the top of the CBL, while horizontal aerosol strata develop at south-facing slopes on the shores of Lake Brienz (Fig. 2). In addition, the CBL height is seen to have already attained - 3000 m asl over pre-alpine topography be'fore advection to high-alpine regions, where it reaches - 4000 m asl. Previous investigations in the upper Rhine valley have observed a CBL top which effectively follows the underlying terrain (Kossmann et al., 1998), and contrasts the level, slightly inclined, features in Figs. 2b and 3b. A long-term synoptic classification of weather over the Alps (Schiiepp, 1979) reveals that winds from the "North" sector (N-NW) have the highest frequency in central Switzerland, suggesting that the atmospheric structure over the Emmental region, as well as over regions further away (Jura, - 1400 m asl; Vosges, ~ 1200 m asl) may be important in development of the CBL over high-alpine regions. ACKNOWLEDGEMENTS The financial support of the NERC and EU funded STAAARTE programme are kindly acknowledged. REFERENCES HoffR. M., HarwoodM., SheppardA., FroudeF. A., MartinJ. B. and StrappJ. W. (1997)Atmos. Environ., 31, 2123-2134. Kossmann M., Vrgtlin R., Corsmeier U., Vogel B., Fiedler F., Binder H.-J., Kalthoff N. and Beyrich F. (1998) Atmos. Environ., 32, 1323-1348. Nyeki S., Kalberer M., Lugauer M., Weingartner E., Petzold A., Schrrder F., Colbeck I. and Baltensperger U. (1999) Submitted to Geophys. Res. Lett. SchiJeppM. (1979) Klimatologieder Schweiz,Beilage zu den Annalen 1978, Swiss MeteorologicalInstitute.
Pergamon
0021-8502/99/$ - see frontmatter
A I R B O R N E L I D A R STUDY OF C O N V E C T I V E BOUNDARY L A Y E R DEVELOPMENT OVER PRE-ALPINE TERRAIN S. Nyeki ~'2, S. de Wekker 3, D. Steyn3, M. Kossmann 4, M. Kalberer 1, I. Colbeck 2 and U. Baltensperger I l Paul Scherrer Institute, 5232 Villigen PSI, Switzerland 2 Institute for Environ. Res., University of Essex, Colchester, Essex, England 3 Dept. of Geography, University of British Columbia, Vancouver, Canada n Dept. of Geography, University of Canterbury, Christchurch, New Zealand
KEYWORDS CBL, lidar, pre-alpine terrain, European Alps The structure of the convective boundary layer (CBL) and the exchange of CBL air masses with the free troposphere (FT) over complex mountainous terrain, is at present poorly understood. More recent studies have begun to use airborne lidar to observe CBL development over large spatial scales, such as the Pacific 93 campaign in the Lower Fraser Valley near Vancouver (e.g. Hoff e t a l . , 1997). The forthcoming Intensive Observation Period of the Mesoscale Alpine Project (MAP) over the European Alps in September 1999 will allow a comprehensive study to be conducted within the framework of an extensive airborne and ground-based measurement programme. In preparation for MAP, preliminary investigations were performed during an airbome campaign over the Jungfraujoch 46.-~ high-alpine research station (JFJ; 3454 m asl) Switzerland on 30 July 1997, in which 46. aerosol (Nyeki e t a l . , 1999) and lidar measurements were conducted. The present work focuses on development of the CBL 46. structure over the following regions shown in Fig. 1: a) pre-alpine terrain (500 - 2000 m asl) 46. in the Emmental region upwind of the JFJ, and b) over Lake Brienz (564 m asl). An extensive anticyclone was located over 46. central Europe, resulting in clear conditions with a light wind from the northwest (305 46.~ 315°). Radiosonde profiles for a pre-alpine location (Payeme, CH; 490 m asl, 85 km distant, WNW) confirmed a stable 46.: atmospheric stratification in the free troposphere ( d O / d z ~ 5.5 K km l for 3 - 5 km 46.1 7.60 7.70 7.80 7.90 8.00 8.10 8.20 8.30 8.40 asl). Moming (0100 LST; = UTC + 1) and afternoon (1300 LST) profiles indicated a Fig. 1. Map of the JFJ region indicating the subsidence inversion at about 2650 m asl. A nominal flight pattern of lidar transects at 8.0 downward-looking aerosol lidar (~ = 532 nm) km asl. Topographical elevation intervals at 1.0 aboard the German Aerospace Establishment km, darkest interval 3.0 - 4.0 km asl. For details (DLR) Falcon 20 jet aircraft was used to monitor atmospheric structure below 8 km of transects see text.
$209
$210
O~
Abstracts of the 1999 EuropeanAerosolConference
,
,
7.70
7.75
7,80
,t
7,70
7.75
7.80
7.85
7.85 Longitude
7,90
7,95
7.90
7.95
46.50
8.00
,~4o
46.60
46.~L~ti~¢ N46.~o
46.70
46.80
46.70
E
Fig. 2. Comparison of O1 transects during: a) the morning (0735 LST) and b) afternoon (1350 LST) flight. Lake Brienz lies east of 7.88°E.
Fig. 3. Comparison of P5 transects during: a) the morning (0815 LST) and b) afternoon LST) flight. Lake Brienz lies at 46.70°N [with the Emmental region north of this point.
1(1425
asl. Multiple passes were flown within a 40 x 75 km horizontal domain centred over the JFJ, where the five main transects were near-parallel to the wind and orthogonal to the regional alpine divide (see Fig. 1). Lidar results from identical morning and afternoon flight patterns over Lake Brienz (transect O1) are shown in Fig. 2a-b, respectively, and over a pre/high-alpine transect (transect P5) in Fig. 3a-b. Morning convective activity in the Emmental region (north of 46.70°N in Fig. 3a-b) is already seen to have begun and results in some cloud formation above south-facing slopes by the afternoon. Enhanced backscatter over Lake Brienz is most probably due to the hygroscopic growth of aerosols, rather than due to anthropogenic pollution, in this instance. A number of interesting features are evident. Convective cells are apparent in irregularities at the top of the CBL, while horizontal aerosol strata develop at south-facing slopes on the shores of Lake Brienz (Fig. 2). In addition, the CBL height is seen to have already attained - 3000 m asl over pre-alpine topography be'fore advection to high-alpine regions, where it reaches - 4000 m asl. Previous investigations in the upper Rhine valley have observed a CBL top which effectively follows the underlying terrain (Kossmann et al., 1998), and contrasts the level, slightly inclined, features in Figs. 2b and 3b. A long-term synoptic classification of weather over the Alps (Schiiepp, 1979) reveals that winds from the "North" sector (N-NW) have the highest frequency in central Switzerland, suggesting that the atmospheric structure over the Emmental region, as well as over regions further away (Jura, - 1400 m asl; Vosges, ~ 1200 m asl) may be important in development of the CBL over high-alpine regions. ACKNOWLEDGEMENTS The financial support of the NERC and EU funded STAAARTE programme are kindly acknowledged. REFERENCES HoffR. M., HarwoodM., SheppardA., FroudeF. A., MartinJ. B. and StrappJ. W. (1997)Atmos. Environ., 31, 2123-2134. Kossmann M., Vrgtlin R., Corsmeier U., Vogel B., Fiedler F., Binder H.-J., Kalthoff N. and Beyrich F. (1998) Atmos. Environ., 32, 1323-1348. Nyeki S., Kalberer M., Lugauer M., Weingartner E., Petzold A., Schrrder F., Colbeck I. and Baltensperger U. (1999) Submitted to Geophys. Res. Lett. SchiJeppM. (1979) Klimatologieder Schweiz,Beilage zu den Annalen 1978, Swiss MeteorologicalInstitute.