Busato M.

Pecorari E.

Rampazzo G.

Archivio Istituzionale della Ricerca

Planetary Boundary Layer: a model validation.

PECORARI, ELIANA

RAMPAZZO, Giancarlo

Archivio istituzionale della ricerca - Università degli Studi di Venezia Ca' Foscari

 PLANETARY BOUNDARY LAYER: A MODEL VALIDATION  Eliana Pecorari1, Martina Busato1and Giancarlo Rampazzo1   1Department of Environmental Science, Informatics and Statistics, University Ca’ Foscari Venice, Calle Larga Santa Marta 2137, Dorsoduro 30121 Venice, Italy.  The diurnal variation of various meteorological parameters in the Planetary Boundary Layer at different altitudes has been studied through a remote sensing instrumentation and a sonic anemometer. RASS-SODAR integrated system allowed the definition of the vertical temperature profiles and the determination of the vertical wind speed and direction profiles. The Sonic Anemometer provided the dataset used to obtain the time trend of other meteorological and dispersive parameters, and to evaluate the PBL turbulence and heat exchange.  Key words: Planetary Boundary Layer, Rass/Sodar measurements, meteorological modeling.    INTRODUCTION Meteorological conditions strongly affect secondary pollutants formation. Complex and non linear processes, in fact, are involved in pollutants production and accumulation. Understanding meteorological parameters behavior is important especially for wind and temperature profiles in the Planetary Boundary Layer (PBL) where air pollutants dispersion is more dangerous for human health. Unfortunately upper data are not easily available and measurements entail high costs. Meteorological models, usually used as dispersion pre-processor, can help to overcome this problem.  A new project has been conducted in Venice area to better understand PBL conditions. Particular attention has been given to lagoon affection on PBL dynamics.  METHODOLOGY The diurnal variation of various meteorological parameters in the Planetary Boundary Layer has been studied through a remote sensing instrumentation and a sonic anemometer. RASS-SODAR integrated system allowed the determination of the vertical temperature profiles and of the vertical wind speed and direction profiles. The Sonic Anemometer provided the dataset used to obtain the time trend of other meteorological and dispersive parameters, and to evaluate the PBL turbulence variables and the energetic fluxes. The mobile RASS- Airone provided by ISMES-CESI was installed on board a 13 m semi-trailer carrying a container containing acquisition electronics, Doppler radar and an acoustic generator. Remote measurement takes place when the acoustic generator emits a brief impulse upward and the corresponding radio echo captured by the Doppler radio receiver antenna is analyzed. The SODAR LP-120 was provided by ISMES-CESI and is composed by three individual antennas aimed in specific directions to steer the acoustic beam. The Sonic Anemometer METEK-USA 1, provided by ISMES-CESI uses ultrasonic sound waves to measure wind velocity. They measure wind speed based on the time of flight of sonic pulses between 3 pairs of transducers. The instrumentation is connected with a data capture system Meteoflux®, that allow to collect real time data of the three wind component and of the eddy covariance requested for the calculation of turbulence parameter and of radiation fluxes. The anemometer was coupled with a meteorological station to measure local temperature, pressure, humidity and precipitation. Several sensors have been located to collect radiation and heat flux data. The instrumentation is showed in Figure 1.   Figure 1. Rass/Sodar station with the Sonic Anemometer.   The monitoring stations have been located in strategic areas of the Venice Lagoon (Porto, the lagoon site, and Malamocco, the sea site) and for two different periods (autumn-winter and spring-summer, respectively). Other data has been obtained by a RASS-SODAR integrated system located in Fusina, which works in continuous for the entire year (Figure 2). Unfortunately only one instrumentation was available and the two campaigns were conducted in different periods. Data was collected from the September 2009 to the Dicember 2009 in the lagoon site and from march 2010 to July 2010 in the sea site. Data from the fixed instrument in land site were always available so comparison between land and lagoon site were made for the first period, and comparison between land and sea site were made for the second one. Logistic problems didn’t allow to collect nocturnal data in lagoon site and to have always coherent data among the three stations.  Measurements have been used to validate a diagnostic meteorological model (MINERVE) (Desiato et al., 1998, Aria Technologies, 2001) and a turbulence model (SURFPRO) (D'Allura et al., 2004). Minerve is a 3D wind field model for complex terrains; it produces a mass-consistent wind field with data from a dispersed meteorological network. Temperature and humidity fields can also be interpolated. SURFPRO produces the fields of dry deposition velocities and turbulent diffusivities.     Figure 2. Sample sites location in Venice area.  DATA ANALYSIS Daily variability of Planetary Boundary Layer don’t permit an homogeneous analysis only based on average values. Besides this a general and typical behavior has been checked for the sites investigated. From RASS data temperature profiles were plotted while wind ones was get by SODAR measurements. The anemometer allowed to measure other parameters that are significant in heat exchange and in dispersion phenomena such as: global and net radiation, stability class and mixing height and wind component standard deviation. All these parameters have a cyclical behavior and are influenced by solar radiation and by meteorological phenomena like clouds or precipitation. Unfortunately land site wasn’t supplied with an anemometer and data couldn’t have been compared. In the first period PBL profiles show significant correlations between land and lagoon sites at different heights for both wind (0.6 ÷ 0.8, with p < 0.5) and temperature (0.9, with p < 0.5) data. During the second period correlations show significant values for temperature profiles (0.7 ÷ 0.9, with p < 0.5) while wind values are not well correlated (0.3÷ 0.5, with p < 0.5) at different heights. Temperature profiles show a typical daily behavior in all the sites investigated but land site is generally warmer than the other two sample stations. unfortunately lagoon and sea data don’t reach more than 600 m of heights because the mobile instrumentation was less powerful than the fixed one in land site. Some peculiarities can be observed temperature profiles. As regard the first period generally an early inversion occurs in the lagoon site from 3 pm probably connected with the formation of the stable nocturnal layer. That doesn’t happen for land site where it arises from 6 to 8 pm. Unfortunately lack of nocturnal data doesn’t allow to observe the profile for the 24 hours. The differences between the two sample sites can depend on PBL behavior for different geographic positions. An example of absolute temperature profile during the day for the first period is showed in Figure 3.    Figure 3. Land and lagoon comparison of temperature profiles.  Wind profiles confirm the typical Venice climatology with calm wind and breeze. Wind speed increases with height reaching high values over 150 m or over the elevated inversion height defined by temperature profiles. Land site wind is generally lower respect to the sea sites while lagoon present more comparable values at the different heights The first period is characterized by highest wind values in the morning while the second one shows nocturnal more windy situations.  The anemometer data were processed by Meteoflux® System and refer to weather parameters,  wind components and energetic fluxes. Data were available only for lagoon and sea sites. These parameters are generally used for weather analysis or as modeling input. An inverse proportionality exist between solar radiation and stability classes that means very unstable situations during the day (value 1-2, class A-B of Beaufort scale) with high solar radiation and convective turbulence phenomena. Nocturnal period is characterized by stability (value 4, class D of Beaufort scale) that means mechanical turbulence phenomena. During the night or during in the early morning the value 6 (F of Beaufort scale) denotes foggy events.  MODELING Data predicted were compared with measurements for the two periods. Generally the model tends to make homogeneous the data over the study area than reality and the vertical profiles are strongly influenced by upper air data used as input of the simulation. Differences appear more in the lower levels than over the 100 m height. An example for temperature data is showed in Figure 4). Despite this, comparison shows a good correlation between predicted and measured except for data near the surface. That is probably due to the fact that surface meteorological data used by the model are interpolated among a big number of local stations, while measured data refers to a unique value.   Figure 4. Comparison between predicted and measured data, land – lagoon case.  CONCLUSION Temperature and wind profiles are strongly correlated to heat exchange between earth and atmosphere as explained before. Data for heat exchange were necessary to better describe the PBL behavior. Data from lagoon and sea sites were available and some critical situations was stressed confirming the analysis described before. During the first period lagoon site shows a very stable situation in first hours of the night probably connected with the early inversion described before. This situation can be critical if emission sources are located in the area because pollution won’t be dispersed easily. During summer period the sea site is characterized by daily strong instability at the lower heights and elevated inversion causing the typical capping inversion. Adding a calm wind situation to this typical PBL behavior will increase the risk of pollutant entrapment. As regard modeling, some critical situation arise by data comparison. The temperature profile in the sea site seems to be discriminant respect to the other stations. That can depend on model but also on a real particular geographical position that is affected by the sea influence. Even though data demonstrate a good performance of the model, results can be improved with an increase of model data input with new measurements.  This work was supported by Ente della Zona Industriale di Porto Marghera and ISMES (Divisione Ambiente e Territorio di CESI Spa). The authors also express thanks to ARIANET Srl and MAV for helping in collecting meteorological data.  REFERENCES Aria Technologies, 2001: Aria Technologies, MINERVE Wind Field Models Version 7.0, General Design Manual ARIA Report, Aria Technologies, Paris (May 2001). D’Allura, A., R. De Maria, M. Clemente, F. Lollobrigida, S. Finardi, C. Silibello and G. Brusasca, 2004: The influence of surface atmosphere exchange processes on ozone levels. In: Sunden, B., Brebbia, C.A., Mendes, A.C. (Eds.), Advanced Computational Methods in Heat Transfer, VIII, 265-275. Desiato F., S. Finardi, G. Brusasca and M.G. Morselli 1998: TRANSALP 1989 Experimental Campaign - Part I: Simulation of 3-D Flow with Diagnostic Wind Field Models. Atmospheric Environment, 32, 7, 1141-1156.  

Name not available

 PLANETARY BOUNDARY LAYER: A MODEL VALIDATION 
 
Eliana Pecorari1, Martina Busato1and Giancarlo Rampazzo1  
 
1Department of Environmental Science, Informatics and Statistics, University Ca’ Foscari Venice, Calle Larga Santa Marta 
2137, Dorsoduro 30121 Venice, Italy. 
 
The diurnal variation of various meteorological parameters in the Planetary Boundary Layer at different altitudes has been studied through a 
remote sensing instrumentation and a sonic anemometer. RASS-SODAR integrated system allowed the definition of the vertical temperature 
profiles and the determination of the vertical wind speed and direction profiles. The Sonic Anemometer provided the dataset used to obtain 
the time trend of other meteorological and dispersive parameters, and to evaluate the PBL turbulence and heat exchange. 
 
Key words: Planetary Boundary Layer, Rass/Sodar measurements, meteorological modeling.  
 
 
INTRODUCTION 
Meteorological conditions strongly affect secondary pollutants formation. Complex and non linear processes, in fact, are 
involved in pollutants production and accumulation. Understanding meteorological parameters behavior is important 
especially for wind and temperature profiles in the Planetary Boundary Layer (PBL) where air pollutants dispersion is more 
dangerous for human health. Unfortunately upper data are not easily available and measurements entail high costs. 
Meteorological models, usually used as dispersion pre-processor, can help to overcome this problem.  
A new project has been conducted in Venice area to better understand PBL conditions. Particular attention has been given to 
lagoon affection on PBL dynamics. 
 
METHODOLOGY 
The diurnal variation of various meteorological parameters in the Planetary Boundary Layer has been studied through a 
remote sensing instrumentation and a sonic anemometer. RASS-SODAR integrated system allowed the determination of the 
vertical temperature profiles and of the vertical wind speed and direction profiles. The Sonic Anemometer provided the 
dataset used to obtain the time trend of other meteorological and dispersive parameters, and to evaluate the PBL turbulence 
variables and the energetic fluxes. 
The mobile RASS- Airone provided by ISMES-CESI was installed on board a 13 m semi-trailer carrying a container 
containing acquisition electronics, Doppler radar and an acoustic generator. Remote measurement takes place when the 
acoustic generator emits a brief impulse upward and the corresponding radio echo captured by the Doppler radio receiver 
antenna is analyzed. The SODAR LP-120 was provided by ISMES-CESI and is composed by three individual antennas 
aimed in specific directions to steer the acoustic beam. The Sonic Anemometer METEK-USA 1, provided by ISMES-CESI 
uses ultrasonic sound waves to measure wind velocity. They measure wind speed based on the time of flight of sonic pulses 
between 3 pairs of transducers. The instrumentation is connected with a data capture system Meteoflux®, that allow to 
collect real time data of the three wind component and of the eddy covariance requested for the calculation of turbulence 
parameter and of radiation fluxes. The anemometer was coupled with a meteorological station to measure local temperature, 
pressure, humidity and precipitation. Several sensors have been located to collect radiation and heat flux data. The 
instrumentation is showed in Figure 1. 
 
 
Figure 1. Rass/Sodar station with the Sonic Anemometer. 
 
 
The monitoring stations have been located in strategic areas of the Venice Lagoon (Porto, the lagoon site, and Malamocco, 
the sea site) and for two different periods (autumn-winter and spring-summer, respectively). Other data has been obtained by 
a RASS-SODAR integrated system located in Fusina, which works in continuous for the entire year (Figure 2). Unfortunately 
only one instrumentation was available and the two campaigns were conducted in different periods. Data was collected from 
the September 2009 to the Dicember 2009 in the lagoon site and from march 2010 to July 2010 in the sea site. Data from the 
fixed instrument in land site were always available so comparison between land and lagoon site were made for the first 
period, and comparison between land and sea site were made for the second one. Logistic problems didn’t allow to collect 
nocturnal data in lagoon site and to have always coherent data among the three stations. 
 
Measurements have been used to validate a diagnostic meteorological model (MINERVE) (Desiato et al., 1998, Aria 
Technologies, 2001) and a turbulence model (SURFPRO) (D'Allura et al., 2004). Minerve is a 3D wind field model for 
complex terrains; it produces a mass-consistent wind field with data from a dispersed meteorological network. Temperature 
and humidity fields can also be interpolated. SURFPRO produces the fields of dry deposition velocities and turbulent 
diffusivities. 
 
 
 
 
Figure 2. Sample sites location in Venice area. 
 
DATA ANALYSIS 
Daily variability of Planetary Boundary Layer don’t permit an homogeneous analysis only based on average values. Besides 
this a general and typical behavior has been checked for the sites investigated. From RASS data temperature profiles were 
plotted while wind ones was get by SODAR measurements. The anemometer allowed to measure other parameters that are 
significant in heat exchange and in dispersion phenomena such as: global and net radiation, stability class and mixing height 
and wind component standard deviation. All these parameters have a cyclical behavior and are influenced by solar radiation 
and by meteorological phenomena like clouds or precipitation. Unfortunately land site wasn’t supplied with an anemometer 
and data couldn’t have been compared. 
In the first period PBL profiles show significant correlations between land and lagoon sites at different heights for both wind 
(0.6 ÷ 0.8, with p < 0.5) and temperature (0.9, with p < 0.5) data. During the second period correlations show significant 
values for temperature profiles (0.7 ÷ 0.9, with p < 0.5) while wind values are not well correlated (0.3÷ 0.5, with p < 0.5) at 
different heights. 
Temperature profiles show a typical daily behavior in all the sites investigated but land site is generally warmer than the other 
two sample stations. unfortunately lagoon and sea data don’t reach more than 600 m of heights because the mobile 
instrumentation was less powerful than the fixed one in land site. Some peculiarities can be observed 
temperature profiles. As regard the first period generally an early inversion occurs in the lagoon site from 3 pm probably 
connected with the formation of the stable nocturnal layer. That doesn’t happen for land site where it arises from 6 to 8 pm. 
Unfortunately lack of nocturnal data doesn’t allow to observe the profile for the 24 hours. The differences between the two 
sample sites can depend on PBL behavior for different geographic positions. An example of absolute temperature profile 
during the day for the first period is showed in Figure 3. 
 
 
 
Figure 3. Land and lagoon comparison of temperature profiles. 
 
Wind profiles confirm the typical Venice climatology with calm wind and breeze. Wind speed increases with height reaching 
high values over 150 m or over the elevated inversion height defined by temperature profiles. Land site wind is generally 
lower respect to the sea sites while lagoon present more comparable values at the different heights The first period is 
characterized by highest wind values in the morning while the second one shows nocturnal more windy situations. 
 
The anemometer data were processed by Meteoflux® System and refer to weather parameters,  wind components and 
energetic fluxes. Data were available only for lagoon and sea sites. These parameters are generally used for weather analysis 
or as modeling input. An inverse proportionality exist between solar radiation and stability classes that means very unstable 
situations during the day (value 1-2, class A-B of Beaufort scale) with high solar radiation and convective turbulence 
phenomena. Nocturnal period is characterized by stability (value 4, class D of Beaufort scale) that means mechanical 
turbulence phenomena. During the night or during in the early morning the value 6 (F of Beaufort scale) denotes foggy 
events. 
 
MODELING 
Data predicted were compared with measurements for the two periods. Generally the model tends to make homogeneous the 
data over the study area than reality and the vertical profiles are strongly influenced by upper air data used as input of the 
simulation. Differences appear more in the lower levels than over the 100 m height. An example for temperature data is 
showed in Figure 4). Despite this, comparison shows a good correlation between predicted and measured except for data near 
the surface. That is probably due to the fact that surface meteorological data used by the model are interpolated among a big 
number of local stations, while measured data refers to a unique value. 
 
 
Figure 4. Comparison between predicted and measured data, land – lagoon case. 
 
CONCLUSION 
Temperature and wind profiles are strongly correlated to heat exchange between earth and atmosphere as explained before. 
Data for heat exchange were necessary to better describe the PBL behavior. Data from lagoon and sea sites were available 
and some critical situations was stressed confirming the analysis described before. During the first period lagoon site shows a 
very stable situation in first hours of the night probably connected with the early inversion described before. This situation 
can be critical if emission sources are located in the area because pollution won’t be dispersed easily. During summer period 
the sea site is characterized by daily strong instability at the lower heights and elevated inversion causing the typical capping 
inversion. Adding a calm wind situation to this typical PBL behavior will increase the risk of pollutant entrapment. 
As regard modeling, some critical situation arise by data comparison. The temperature profile in the sea site seems to be 
discriminant respect to the other stations. That can depend on model but also on a real particular geographical position that is 
affected by the sea influence. Even though data demonstrate a good performance of the model, results can be improved with 
an increase of model data input with new measurements. 
 This work was supported by Ente della Zona Industriale di Porto Marghera and ISMES (Divisione Ambiente e 
Territorio di CESI Spa). The authors also express thanks to ARIANET Srl and MAV for helping in collecting 
meteorological data. 
 
REFERENCES 
Aria Technologies, 2001: Aria Technologies, MINERVE Wind Field Models Version 7.0, General Design Manual ARIA 
Report, Aria Technologies, Paris (May 2001). 
D’Allura, A., R. De Maria, M. Clemente, F. Lollobrigida, S. Finardi, C. Silibello and G. Brusasca, 2004: The influence of 
surface atmosphere exchange processes on ozone levels. In: Sunden, B., Brebbia, C.A., Mendes, A.C. (Eds.), 
Advanced Computational Methods in Heat Transfer, VIII, 265-275. 
Desiato F., S. Finardi, G. Brusasca and M.G. Morselli 1998: TRANSALP 1989 Experimental Campaign - Part I: Simulation 
of 3-D Flow with Diagnostic Wind Field Models. Atmospheric Environment, 32, 7, 1141-1156. 
 


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Planetary Boundary Layer: a model validation.

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