Technical report on meteorological measurements carried out in urban and sub-urban areas of Rome in the frame of EXPAH project. Action 3.4

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Technical report on meteorological measurements carried out in urban and sub-urban areas of Rome in the frame of

EXPAH project. Action 3.4

C. Gariazzo¹, S. Argentini², I. Pietroni², A. Pelliccioni¹, I. Petenko²

1 INAIL , Ex-ISPESL, Dipartimento Installazioni di Produzione e Insediamenti Antropici

2 CNR, Istituto Scienze dell’Atmosfera e del Clima, Unità Tor Vergata-Roma

September, 2012

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2 List of content

Executive summary ... 3

1. Introduction ... 4

2. Measurements sites and instrumentation ... 4

2.1. Villa Pamphili ... 5

2.2. Tor-Vergata Science park ... 9

2.3. Montelibretti ... 14

2.4. Monteporzio Catone ... 15

2.5. Preliminary data processing. ... 16

3. Statistical analysis of wind measurements on seasonal and annual bases ... 16

3.1. Seasonal and annual wind roses ... 16

3.2. Daily histogram of wind speed and direction ... 19

4. Statistical analysis of surface air temperature and humidity on seasonal and annual bases ... 24

4.1. Probability density function (PDF) of surface air temperature and humidity ... 24

4.2. Daily histogram of surface air temperature and humidity ... 28

5. Statistical analysis of surface turbulence parameters on seasonal and annual bases ... 31

5.1. Probability density function of friction velocity, turbulent kinetic energy, standard deviation of vertical wind speed and Monin-Obukhov length ... 31

5.2. Daily histogram of surface turbulence parameters ... 35

6. Characterization local circulation systems ... 41

6.1. Sea breezes ... 41

6.2. Cold fronts ... 43

6.3. Warm fronts ... 45

6.4. Urban vertical structure of wind. ... 47

Conclusions ... 50

References ... 52

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3 Executive summary

The action 3.4 of EXPAH project carried out a field campaign to collect meteorological data in the urban area of Rome and its surroundings. The aims of the field experiment is to detect the main local circulation patterns and provide data to action 4.5 to reconstruct the meteorological fields by means of a modeling system. Four measurements sites equipped with in situ and ground based remote sensing systems were used.

The field campaign started on December 2010 and ended on June 2012. The 2011 data were preprocessed for validation and averaged on a hourly base. More than 35000 meteorological measurements (4 x 365 x 24) were produced, each of them composed by multi-parameters.

In order to obtain information on the typical behavior of the different parameters, a statistical analysis has been done on 2011 data set.

For the wind we extracted the wind roses at each station, for the whole year and on seasonal bases using both surface and upper air data (100 and 180m a.g.l.). The prevalent winds were identified. The probability density functions were also calculated to get the occurrences of wind speed and directions on both yearly and seasonal bases. The hourly occurrence of the wind at each station provided information of the daily evolution of wind.

Also for the air temperature and the relative humidity the probability density functions were calculated to obtain the occurrence of specific values of these parameters on both yearly and seasonal bases. For the wind the hourly distributions were calculated to get information on the most likely value at any hour of a typical day.

As turbulence has a great impact on pollutants concentration, we carried out a statistical study on some parameters considered descriptors of surface turbulence: friction velocity; turbulence kinetic energy; standard deviation of vertical wind component and stability parameter. Also for these parameters the probability density functions were calculated on yearly, seasonally and hourly bases.

Information on their typical behavior were extracted.

The typical meteorological regimes were identified and presented for some representative days.

The sea-breeze, cold and warm fronts were detected and characterized. A peculiar vertical wind structure was detected at the urban station during the early morning hours of cloudless days and stable conditions, in presence of an high pressure system.

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4 1. Introduction

The EC funded the EXPAH project (EXPAH “Population Exposure to PAHs”) under the LIFE+ program.

The aim of EXPAH is to identify and quantify the population exposure to Polyciclic Aromatic Hydrocarbon (PAH) in highly urbanized areas, and to assess the impact of the PAH on human health.

The action 3.4 of the EXPAH project is responsible for the collection of meteorological measurements which are required to feed the modeling system that simulate the emission, dispersion and transformation of PAH in the target studied area, chosen to be the metropolitan area of Rome, Italy, carried out under action 4.5.

Since December 2010 the project has collected upper air and surface meteorological data. In addition to the existing monitoring network, four stations have been located in the city of Rome and its surroundings. Remote sensing systems are used in this intensive field campaign as well as sensors for the measurement of the atmospheric turbulence. In addition, to feed the modeling systems, the collected meteorological data allow to monitor the spatial extensions of the meteorological phenomena, identifying urban effects and the observation of both mountain-valley and sea-land circulations in the basin area. Statistical analysis is a common approach to detect, characterize and parameterize such effects. The local circulation regimes around the city of Roma has been studied by different authors [eg. Petenko et at (2011); Pelliccioni et al. (2012); Gariazzo et al. (2010);

Mastrantonio et al. (2006; 2008)]. The local circulation is characterized by two prevailing circulations:

land and sea breezes, and drainage flows from the mouth of the Tiber valley. Daily behavior of the wind direction and intensity, as a function of the season, was highlighted by these studies and the existence of two nocturnal alternative components of the local circulation was evidenced.

The following chapters will describe the statistical analysis carried out on the meteorological data collected under the EXPAH project and the differences and peculiarities of the data provided by each station to confirm the above regimes and to detect urban influences.

2. Measurements sites and instrumentation

Since December 2010 the EXPAH project has collected upper air and surface meteorological data, closing its intensive field campaign on June 2012. In addition to the existing monitoring network, four stations have been located in the city of Rome, which is the study area, and its surroundings. The meteorological stations are the following:

 Villa Pamphili urban park (hereafter PMH)

 Tor- Vergata science park (hereafter TV)

 Montelibretti CNR-science park (hereafter MLB)

 Monteporzio Catone INAIL Institute (hereafter MTP)

The figure 2.1 and 2.2 show the locations of the four stations in a large and detailed view respectively.

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Figure 2.1. Location of EXPAH meteorological stations.

Figure 2.2. Detailed view of the location of the EXPAH meteorological stations respect to the urban area of Rome.

In the first two stations, upper air (by means of remote sensing systems) and surface meteorological measurements are carried out. Surface turbulence measurements are conducted at the same sites.

The last two stations provide simple conventional meteorological measurements. Details about each station are given below.

2.1. Villa Pamphili

The PAMPHILI station is located within the Villa Pamphili urban park, NorthWest of Rome. The park is embedded in the urban structures about 4 Km from the downtown area. Figure 2.3 shows details about its location in the city of Rome. The meteorological station is composed by a mobile laboratory (LMM) and two ground based remote sensing systems. The LMM system (figure 2.4) hosts several surface meteorological equipments able to measure both conventional and unconventional parameters such as those related with atmospheric turbulence. The list of measured parameters is shown in table 2.1.

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Figure 2.3. Details about the location of the PAMPHILI station.

Figure 2.4. The Meteorological Mobile Laboratory at the PAMPHILI station.

Table 2.1. List of meteorological parameters measured by the mobile laboratory LMM.

parameter unit

Wind speed at 10 and 2m Standard dev. Wind speed at 10 and 2m Horizontal wind direction at 10 and 2m Standard dev. Wind direction at 10 and 2m

Vertical wind speed at 10 and 2m Standard dev. Vertical wind speed at 10 and

2m Air temperature at 10 and 2m global solar radiation

rain quantity air temperature at 2m

relative humidity net solar radiation

soil temperature

differential temperature between 10-2m atmospheric pressure

m/s m/s degree N

degree m/s m/s

°C watt/m²

mm

°C

% watt/m²

°C

°C hPa

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By using the two tri-axial sonic anemometers (http://www.gill.co.uk/products/anemometer/windmaster.htm) located at 2 and 10 m above the ground, it is possible to calculate a surface profile of some

atmospheric parameters listed in table 2.2.

Table 2.2. Measured and calculated turbulence parameters by the mobile laboratory LMM.

ACRN Parameter unit

Measured parameters

U V W TS SoS T1 T2

u Component wind speed v Component wind speed w Component wind speed sonic Temperature speed of sound Temperature at 10m Temperature at 2m

m/s m/s m/s

°C m/s

°C

Measurements heights 2 e 10 m

Sampling rate 20 Hz

Derived turbulence parameters

Ndata v_vet v_scal dir Tm s_dir su sv sw TKE sT uv uw vw uT vT wT u_st T_st z_L H0 Cu2 Cv2 Cw2 CT2 T1 T2

Number of data processed Vectorial wind speed Scalar wind speed Wind direction Sonic Temperature

Standard Dev. Wind direction Stand Deviat. u compon wind speed Stand Deviat. v compon wind speed Stand Deviat. w compon wind speed Turbulent kinetic energy

Stand. Dev. sonic Temp.

Covariance comp. u,v wind speed covariance comp. u,w wind speed covariance comp. v,w wind speed covariance Sonic temp. - comp. u wind covariance Sonic temp. - comp. v wind covariance Sonic temp. - comp. w wind friction velocity

Temperature scale Monin-Obukhov lenght sensibile heat

structure Parameter comp. u wind structure Parameter comp.v wind structure Parameter comp. w wind structure Parameter temperature air temperature aria at 2 m air temperature aria at 10 m

m/s m/s degree N K degree N m/s m/s m/s m²/s²

°K m²/s² m²/s² m²/s² m/s K m/s K

°C m/s K

Watt/m² (m/2)² (m/2)² (m/2)² K² K K

In order to obtain vertical profiles of wind and temperature, a ground based remote sensing system was used. It is based on a SODAR/RASS system. A SODAR is an active remote sensing device that vertically emits sound pulses and receives and analyzes the backscattered part reflected from refraction index fluctuations in the atmosphere (Emeis, 2011). By analyzing the Doppler shift of the backscattered sound pulses, it is possible the derivation of the vertical wind profile. Wind and turbulence profiles measurements were performed with a METEK DSDPA.90 (http://www.metek.de/product-details/pcs2000-24.html) phased array miniSODAR. Narrow acoustic beams are achieved by means of a phased array of 16 loudspeakers. The speakers are switched to

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different phases to pan the beam to one of the 3 directions, one of them is directed vertically upward. The system is able to derive the wind components up to 400m agl, and turbulence parameters such as w profile and reflectivity along each beam axis. Diffusion Class (DC) (Pasquill stability), standard deviation of wind direction and inclination (, ) can also be calculated by the system. For this filed campaign the SODAR was set to measure wind up to 400 m agl with a vertical resolution of 20 m and 40 m as lowest measuring height. The system was set to provide analyzed data at 10 minutes period. The collected data were selected for further analysis only if the acceptance test was satisfied. The latter is based on different parameters such as signal to noise ratio and statistical significance of measured signal and ambient noise.

A Radio acoustic sounding system (RASS) is normally coupled with a SODAR system (http://www.metek.de/product-details/id-1290-mhz-rass.html). This instrument is able to detect acoustic shock front of the acoustic pulses and to determine their propagation speed from the Doppler shift of the electromagnetic waves (Emeis, 2011). This propagation speed is equal to the speed of sound, which in turn is known function of air temperature and humidity. For this campaign the RASS system was set to measure temperature at the same heights as the SODAR system.

A picture of the SODAR/RASS system is shown in figure 2.5. A list of measured and derived parameters is reported in table 2.3.

Figure 2.5. The SODAR/RASS system.

Table 2.3. List of measured and derived SODAR/RASS parameters Minimum measurement height 40m

Maximum measurement height 400m

Vertical resolution 20m

ACRON. parameter unità

Measured parameters

RR1 RR2 RR3 VVU VVV VVW V D S3

Reflectivity acoustic axis 1 Reflectivity acoustic axis 2 Reflectivity acoustic axis 3 component u Wind speed component v Wind speed component w Wind speed horizontal wind speed horizontal wind direction

Standard Dev. Vertical wind speed

dB dB dB m/s m/s m/s m/s degree N m/s

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9 DC

TMP

Diffusion class.

virtual Temperature

A-F

°C

Averaging period 10 min

The PAMPHILI station also hosts an additional remote sensing system: a LIDAR ceilometer. In a LIDAR system a light beam is emitted into the atmosphere and interacts with it, mainly in different scattering ways (Emeis, 2011). In particular a backscatter LIDAR is employed to determine aerosol and trace gas profiles in the atmosphere. It detects the backscatter light which depends on the aerosol content in the atmosphere. Ceilometers are simple backscatter LIDARs that record the optical backscatter intensity in the near infrared. Due to its characteristics they are mostly eye-safe and unattended. The Ceilometer installed at the PAMPHILI station is a VAISALA CL31 (http://www.vaisala.com/en/products/ceilometers/Pages/cl31.aspx), which is shown in figure 2.6. Its technical characteristics are given in table 2.4.

Figure 2.6. The LIDAR Ceilometer installed at the PAMPHILI station.

Table 2.4. Technical characteristics of CL31 LIDAR Ceilometer installed at PAMPHILI station.

Parameter value Measurement range 0-7.5 Km

resolution 10 m

source Laser InGaAs diode, 910 nm

Data message Cloud hits, status and backscatter profile

By analyzing the backscatter profile it was possible to obtain information on the vertical structure of the atmosphere through the aerosol vertical distribution. Such data can in turn be used to derive the Planetary Boundary Layer (PBL) heights, particularly the diurnal ones, which cannot be detected by the SODAR/RASS system due to its lower measurement range (0-400 m). Furthermore the backscatter intensity profiles can be used to validate the aerosol model results obtained in a different action of the EXPAH project.

2.2. Tor-Vergata Science park

The Tor-Vergata station is located in the experimental facility of ISAC - CNR research area (41°50’N, 12°38’E). The research area is located 100 m a.s.l. 25 km from the Tyrrhenian sea. At 10 km, in the SE

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direction, the Albani hills (mean altitude 600 m; max altitude 1000 m) lie, while 20 km in the north- west direction the great urban centre of Rome is located. The experimental facility hosts both in situ instruments and ground-based remote sensors to measure meteorological parameters, turbulence and meteorological profiles (wind, temperature, thermal structure of the atmosphere).

A meteorological Automatic Weather Station (AWS) (Figure 2.7) is used to measure the standard meteorological parameters given in table 2.5.

Figure 2.7. The Automatic Weather Station

Table 2.5. AWS measurements

Parameter Units

10 m (sls) 10 m (slm) 3.5 m 3.5 m 3.5 m 3.5 m 3.5 m

VEL DIR T RH PA SR IR

Wind Speed Direction Air Temperature Relative Humidity Atmospheric Pressure Shortwave radiation (down) Infrared Radiation (down)

m s^-1 gradi N

°C

% hPa W m^-2 W m^-2

Acquisition 10 minutes

Averaging time 1 hour

Turbulent fluxes of heat and momentum were measured using Metek USA-1 thermo-anemometers.

Two sonic thermo-anemometer were located on a 10 m mast (Figure 2.8): one at 3.5 m, the other at 10 m. The atmospheric parameters measured or derived using the sonic anemometers are listed in table 2.6.

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Figure 2.8. The micro-meteorological mast Table 2.6. Sonic measurements

Measurements units

Parameter at 3.5 m (sls)

VEL DIR Tson sw u_st L H0 TKE

Average wind speed Average wind direction Sonic temperature Vertical velocity variance Friction velocity

Obukhov length Sensible heat flux Turbulent Kinetic Energy

m s^-1 gradi N

°C m² s^-2 m s^-1 m W m^-2 m²s^-2

Acquisition frequency 10 Hz

The MTP5-P radiometer (Figure 2.9)., used in this study, measures microwave frequency radiation (60GHz) emitted by atmospheric oxygen, to produce a temperature profile with 10m resolution near the ground, increasing to 50m in the upper section of the 600m profile. (Kadygrov and Pick, 1998).

The MTP5 profiler executed a profile scan every 10 minutes, starting on the designated record time and taking approximately 3 minutes to step through the eleven vertical angles, from 1 to 90 degrees elevation. The profiler undertakes a frequent automatic calibration by comparing the temperature measured when the antenna is horizontal with an external reference temperature sensor housed in a standard radiation shield.

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Figure 2.9. The Meteorological Temperature Profiler MTP-5P

Table 2.7. Meteorological Temperature Profiler measurements

Minimum measurement heigth 5 m

Massimum measurement heigth 300 m

Vertical resolution 10 m (0-50 m); 25m (50- 100 m); 50 m (100-300 m)

Measure Unit

Temperature profile 0- 300 m °C

Temporal resolution 10 minutes

Fig 2.10 shows an example of the temperature vs time plot for a 24 hour period. In the upper half and a height vs time plot in the lower half. In the upper plot, all 18 height levels are plotted (plus the surface reference temperature – dark black) which illustrates how the atmosphere commonly makes a transition from an inversion during the night to the daytime regime with no inversion, and the reverse transition in the evening.

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Figure 2.10 24 hour plot of MTP data

A SODAR (Sound Detection and Ranging) Doppler system (Figure 2.11) provided the continuous record of the structure of the atmospheric boundary layer along the year. The SODAR is a triaxial monostatic Doppler system. The antennas radiated 0.1 s duration acoustic bursts simultaneously, each at a different frequency (namely: 1750, 2000, 2250 Hz). The tone bursts, emitted every 6 s, allow for an instrumental range of about 1000 m. The echoes collected by the antennas were separately amplified and filtered, then combined, undersampled at a frequency of 1600 Hz (Mastrantonio and Fiocco 1982) and recorded in a PC file. For each channel, the processing of the returned signal provided the profiles of the radial wind velocity and echo intensity. The three dimensional wind vector can be calculated from the Doppler shift of the echo sent by the three independent radial wind velocities.

Figure 2.11. The triaxial Doppler SODAR

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Table 2.8. Meteorological Temperature Profiler measurements

Minimum height 27 m

Maximum height 1000 m

Vertical resolution 25 m

Measurements units

Parameters RR1

RR2 RR3 VEL DIR VV

Reflectivity acoustic beam 1 Reflectivity acoustic beam 2 Reflectivity acoustic beam 3

Wind Velocity Wind direction Vertical velocity

dB dB dB m s^-1 gradi N

m s^-1

Acquisition frequency 1 measurement/6 s

Averaging 1 hour

Figure 2.12 6 hour plot of SODAR Backscattered echo with superimposed the wind velocity profiles

2.3. Montelibretti

In the CNR–science park of Montelibretti, located about 30 Km north of Rome, a conventional meteorological station was installed. This is a quite rural area with some hills around it. A three meter height mast hosts sensors for air temperature (thermo-resistance PT100) and relative humidity (hygrometer) as well as wind speed (cups anemometer) and direction (wind vane) instruments. The mast, shown in figure 2.13, was mounted on the top of a structure located within the European Monitoring and Evaluation Programme (EMEP) station of Montelibretti, reaching a measurement height of about 5.5 m a.g.l. Table 2.9 summarizes the main parameters and technical characteristics of this station. The collected data are processed by a local control unit and stored in a card memory.

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Figure 2.13. The meteorological station of Montelibretti CNR- science park.

Table 2.9. Parameters measured at the Montelibretti station.

ACRN. Parameter unit

T UR DV VV

Air temperature at 4 m Relative humidity at 4 m

Wind direction at 5.5 m Wind speed at 5.5m

°C

% degree N

m/s

Sampling rate 1 sec

Averaging period 1 h

2.4. Monteporzio Catone

The station of Monteporzio is located within the INAIL Institute, placed about 15 Km south of Rome.

It is sited along the hill of Monteporzio Catone, about 650 m a.s.l., embedded in a group of hills (Albani hill). A picture of the station can be seen in figure 2.14.

Figure 2.14. The Monteporzio meteorological station.

In terms of measured parameters and technical characteristics it is equivalent to that of Montelibretti. The only difference is the measurement heights, which is 3 and 2 m for respectively wind and air temperature and humidity.

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16 2.5. Preliminary data processing.

All data collected at the above stations were validated and, in case of need (eg. SODAR and turbulence data), averaged on hourly bases to provide the data at the time resolution requested by meteorological modeling activities carried out in other EXPAH actions (action 4.5). The processed data were also formatted in predefined text structures to be imported in the meteorological modeling system. Finally the processed data were uploaded to the EXPAH ftp web site (ftp://84.253.168.61) available to be downloaded by other EXPAH users.

3. Statistical analysis of wind measurements on seasonal and annual bases 3.1. Seasonal and annual wind roses

To detect the main features of the wind a statistical approach has been chosen. The wind rose for different velocity ranges has been done. The results give the prevalent wind direction at each station and its characteristic. Figure 3.1 shows the wind roses at the surface for all the stations.

All the stations show a well defined wind pattern with the exception of Tor-Vergata.. At MLB station, the NNW, SW and SE wind sectors prevail. The occurrence in the NNW sector being the prevailing.

Light winds (between 1 - 3 m/s) are the most frequent, while strong winds (> 6 m/s) come from the northern sectors. The urban station of PMH exhibits a stronger wind polarization than the MLB one, with prevalent winds from the N, NE and SW sectors. Strong wind speeds (>6 m/s) are rarely detected as light winds (< 3 m/s) prevail. At TV station all the wind sectors have the same occurrence with the exception of the 210°-240° angular sector. The winds in the W sector are associated to the highest wind velocities (> 4 m/s). Strong winds (> 6 m/s) are observed in all the sectors although with a low occurrence. A strong wind polarization is observed for the MTP station.

The E – SE sectors are the prevailing ones. Light speed (< 2 m/s) are associated to these winds. Due to its particular position (downslope to the hills of Monteporzio Catone) katabatic winds (thermal drainage flows) develop.

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Figure 3.1. Wind roses at EXPAH stations during year 2011.

The PMH and TV SODARs allow to study the vertical profiles of the wind speed and direction. The wind roses were calculated at 2 levels: 100 and 180 m, where at least 50% of measurements are available. The results are shown in figure 3.2.

Figure 3.2. Wind roses at 100 and 180 m calculated from PMH and TV SODARs.

For PMH the measurements at 100 and 180 m are consistent with the surface ones (figure 3.1). For TV some differences are observed between the surface wind roses and 100 – 180 m SODAR ones.

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To highlight the seasonal effects and geographic effects (related with air-surface heat exchange, sea- land breezes and thermally driven local effects) the wind roses have been calculated for all the stations and seasons .

Figure 7. Surface seasonal wind roses at EXPAH stations during year 2011.

Figure 3.3 shows the seasonal wind roses at the surface for each EXPAH station during the year 2011.

At MTB station the winds from the northern west and southern east sectors prevail in all the seasons although with a different strength. Strong wind speed are observed during winter time, normally associated with large scale synoptic flows. Winds from south-west are instead observed during summer and spring with a peak in summer time. These winds are due to the sea breeze which easily develops in this area. According to wind roses, wind speed between 2 and 4 m/s are observed in such conditions.

PMH measurements confirm the presence of the sea breeze from the SW west sector, but with lower wind speeds (2-3 m/s) respect to MTB. The N and NE wind components are instead detected with different strength in all seasons. These winds are more evident during the night or in presence of large scale synoptic conditions. Wind speed above 5 m/s are rare.

During the summer and spring the sea breeze circulation prevails also at TV station. Because of the station position (outside the urban area), stronger wind speed (4-6 m/s) can be observed. NE and E winds prevail during the winter and autumn. These winds are associated to the thermally driven local circulation and to geographic effects produced by the hills located south of the monitoring site.

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v  6 m s^-1 5  v < 6 m s^-1 4  v < 5 m s^-1 3  v < 4 m s^-1 2  v < 3 m s^-1 1  v < 2 m s^-1 0  v < 1 m s^-1 Monteporzio 2011

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At MTP a local katabatic wind prevail during all the seasons. Sea breeze occur during warmer seasons although less evident respect to the other stations.

To verify if seasonal effects are also detected in upper air wind profiles, seasonal wind roses were extracted for the two stations of Pamphili and Tor-Vergata. Figure 3.4 shows the results.

Figure 3.4. Seasonal wind roses at 100 (upper panel) and 180 (lower panel) m from SODAR measurements at PMH and TV stations.

For PMH surface results are roughly the same of the ones at upper level (compare figure 3.3 and 3.4).

In addition a few differences in the wind pattern are observed at 180m for this station. In particular the summer and autumn wind roses seem to be more affected by the seasonal effects. In both seasons the NE wind component was drastically reduced respect to the correspondent values at 100 m.

At the TV the seasonal wind roses at 100 m contain a NE component in all seasons, especially during the winter and autumn.

3.2. Daily histogram of wind speed and direction

The mean daily variation of the meteorological parameters is an important aspect to be investigated, as it provides information of starting and ending time of a certain phenomenon. The hourly PDF functions were calculated for the wind speed and direction at each station. Figures 3.5 and 3.6 show the hourly occurrences of respectively wind speed and direction at the EXPAH stations. The

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v  14 m s^-1 12  v < 14 m s^-1 10  v < 12 m s^-1 8  v < 10 m s-1 6  v < 8 m s^-1 4  v < 6 m s^-1 2  v < 4 m s^-1 0  v < 2 m s^-1 PAMPHILI 2011

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v  14 m s^-1 12  v < 14 m s^-1 10  v < 12 m s^-1 8  v < 10 m s-1 6  v < 8 m s^-1 4  v < 6 m s^-1 2  v < 4 m s^-1 0  v < 2 m s^-1 Tor-Vergata 2011

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v  14 m s^-1 12  v < 14 m s^-1 10  v < 12 m s^-1 8  v < 10 m s^-1 6  v < 8 m s^-1 4  v < 6 m s^-1 2  v < 4 m s^-1 0  v < 2 m s-1

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PAMPHILI 2011

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Tor-Vergata 2011

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