The helicopter-borne ACTOS for
small-scale cloud turbulence observations
Holger Siebert, Katrin Lehmann , Manfred Wendisch, and Raymond Shaw
Leibniz-Institute for Tropospheric Research (IfT), Leipzig, Germany
Dept. of Physics, Michigan Technology University, Houghton, MI, USA
Besides a technical overview of ACTOS the pos-
sibilities of using a helicopter for cloud research are
Clouds play a major role in the Earth system and are discussed by showing measurement examples which
relevant to many aspects of climate and daily weather clearly demonstrate the unique capabilities of the new
forecast. The dynamics of clouds span a wide range system.
of spatial scales from the macroscopic cloud extension
itself down to the Kolmogorov microscale (typically in
the mm range for atmospheric conditions). Since cloud 2. Experimental Setup
microphysical properties on larger scales are controlled
by processes taking place on smaller scales, measure- ACTOS is an autonomous measurement payload which
ments with high spatial and temporal resolution are es- can, in principle, be carried by different platforms such as
sential for a better understanding of cloud processes.
balloons, blimps, Zeppelin, or helicopters. The system is
The majority of airborne in-situ observations of clouds equipped with sensors to perform high-resolution mea-
have been made by fast-flying research aircraft which surements of meteorological standard parameters such
limits the spatial resolution of most parameters to the as wind vector, air temperature, and humidity but also
meter scale or so. To overcome this limitation the Air- cloud and aerosol microphysical properties such as liq-
borne Cloud Turbulence Observation System (ACTOS) uid water content ( ) and number concentrations of
has been developed which was originally designed for interstitial aerosol particles in boundary layer clouds.
the use beneath a tethered balloon (Siebert et al. 2003,
To keep the load for the carrier platform as low as pos-
2006b). Due to the low true airspeed (TAS) of such a sible, a light-weight frame made from carbon-fiber and
balloon-borne system the spatial resolution of the mea- aluminum was designed. The total weight of ACTOS in-
surements is much higher compared with aircraft data. cluding the instruments is
200 kg. ACTOS is equipped
In this paper the new helicopter-borne version of ACTOS with an autonomous power supply and data acquisition
is introduced (see also Siebert et al. (2006a)). However, to be completely independent from its carrier platform. A
compared to balloon–borne measurements, which also data link between ACTOS and the helicopter cabin was
meet the slow–flying criterion, a helicopter is even more installed to ensure on-line monitoring of standard param-
advantageous due to its longer cruising range and pos- eters during the flights.
sible ceiling. A helicopter is more flexible in time and
space than a balloon and can be chartered at different 2a. Sensor Equipment
airfields. Furthermore there are fewer limitations with re- ACTOS was designed to provide collocated measure-
spect to possible payload (weight, size, available electri- ments of several types of parameters. All sensor outputs
are sampled with a joint real-time data acquisition sys-
tem to ensure precise temporal correlation between the
different measured parameters. In the following a short
Cloud droplet microphysical properties are mea-
list of all devices is given, for a more detailed discussion
sured with a modified version of the Fast For-
of sensor performance the reader is referred to Siebert
ward Scattering Spectrometer Probe (M-Fast-FSSP,
et al. (2003, 2006b).
Schmidt et al. 2004; Lehmann et al. 2006). The M-
Fast-FSSP counts each individual droplet and mea-
The three-dimensional wind vector and the vir-
sures its size and the inter-arrival times. The size
tual air temperature are measured with an ultra-
distribution, number concentration, and the of
sonic anemometer/thermometer (Solent HS, see
the droplets is derived from the measurements.
also Siebert and Muschinski 2001).
A combination of differential Global Positioning Sys-
tem (dGPS) and inertial sensors (optical fiber gyros
and accelerometers) measure the attitude angles,
angular rates, position, and the velocity vector of
ACTOS with different time resolution and precision.
A navigation computer combines all measurements
and gives all parameters with 10 Hz resolution (100
Hz are optional) and with best precision.
A special version of the so-called UltraFast Ther-
mometer (UFT, Haman et al. 2001) allows air tem-
perature measurements with 500 Hz resolution. The
UFT is based on temperature-dependent resistance
measurements of a thin wire which is protected
against droplet impaction with a shielding rod in front
of the wire.
Figure 1: Schematic sketch of ACTOS with numbered de-
vices. The system can roughly be divided into three parts (i) the
Humidity fluctuations are measured with a Lyman- tail unit (9), (ii) the main body consisting of five covered 19"-inch
absorption hygrometer. A pre-impactor inlet pre- racks including electronics, data acquisition, power supply, and
vents cloud droplets to enter the optical system dGPS antenna (8) and (iii) an outrigger made of carbon-fiber
which would lead to an irreversible bias of the sig- tubes with all sensor and sampling inlets: 1) Sonic anemome-
ter, 2) M-Fast FSSP, 3) PICT, 4) Impactor Inlets, 5) UFT, 6)
PVM-100A, and 7) Nevzorov probe.
For air temperature and relative humidity measure-
ments standard PT-100 resistance-wire thermome-
ters and a capacitive hygrometer based on the
In addition to the standard equipment a second cloud
Vaisala Humicap sensor serve as calibration stan- spectrometer called PICT (Phase-Doppler Interferome-
dard for the UFT and Lyman- , respectively.
ter for Cloud Turbulence) was installed beside the M-
Fast-FSSP for this experiment. The PICT instrument
The is measured with a Particle Volume Mon-
itor PVM-100A (airborne version, Gerber 1991).
measures the radius, longitudinal velocity component,
and time of arrival of droplets that enter its sampling vol-
The number concentration of interstitial aerosol par- ume. The sampling volume is defined by the region in
ticles is measured with two Condensation Particle which two laser beams intersect: light scattered from
Counter (CPC). Since the two CPCs have a differ- the two beams by a droplet is detected at several an-
ent lower cut-off characteristics, the concentration of gles, providing temporal interference patterns (Doppler
ultrafine particles in the size range between 6 and bursts) related to the droplet size and speed (Bachalo
12 nm is derived which is used as an indicator of and Sankar 1996). The sampling frequency is sufficiently
freshly nucleated particles (Siebert et al. 2004).
high that there is no dead time and therefore inter-droplet
distances as small as the beam cross section can be de-
termined. An advantage of PICT is that droplet sizes
ranging from newly activated cloud droplets to drizzle
can be detected with a single instrument (
m). Furthermore, at low
, such as in the experi-
ment described below, the instrument provides a mea-
sure of the longitudinal turbulent velocity component.
Figure 1 depicts a schematic sketch of the current
version of ACTOS. The setup is divided into three major
parts: i) the 1.5 m long outrigger on which all sensors
and inlets are attached, ii) the main body consisting of
five covered 19" standard racks including the sensor
electronics, data acquisition and power supply, and
iii) the tail unit which keeps ACTOS in the mean flow
direction. A rough skid system with shock absorbers
ensure a safe take-off and landing procedure. The side
covers can easily be removed for final settings before
2b. ACTOS Carried by Helicopter
Figure 2: Sketch of ACTOS suspended from the helicopter of
Using the Helipod system Bange and Roth (1999) and type BELL LongRanger. The rope is 140 m long, several flags
Muschinski et al. (2001) demonstrated that state-of- are attached to the rope to increase the visibility. The down-
the-art turbulence measurements with a payload car- wash from the main rotor blades is deflected backwards, thus,
ried by helicopter as external cargo are possible. With turbulence measurements on ACTOS are safely unbiased. The
sketch is not in scale.
the appropriate combination of
and length of the
rope, measurements are unbiased from the influence
of the helicopter downwash which is deflected back-
wards. However, these measurements were done un-
der cloud-free conditions and no experience was avail-
10.000 ft (3.000 m)
able concerning helicopter flights with an external cargo
Minimum Cloud Base
3.000 ft (1.000 m)
in clouds. After clarification of the flight regulations under
such conditions first test flights with a mock-up version of
ACTOS were successfully performed in 2004 and 2005.
Hereby, ACTOS was dipped into the clouds from above
whereas the helicopter remains outside the clouds such Table 1: Overview of flight parameters and conditions for the
that it can be flown under visual flight regulations (VFR). helicopter-borne ACTOS.
is the true air speed during
For this reason a 140 m long rope was used which is measurement flight conditions, whereas
much longer than the 15 m rope used for the Helipod mum
for carrier flights with ACTOS to the measurement
but has also the advantage of allowing lower
without being influenced
by the downwash. Figure 2 shows a sketch of the com-
For this study a single-engine helicopter of type Bell
bination of ACTOS and the helicopter.
Long Ranger (BELL 206III LR) was used. For VFR
The conditions and requirements for measurement flights one pilot and three scientists/operators can be on
flights with ACTOS are summarized in Tab. 1.
board the helicopter. Flights with the helicopter inside
the clouds have to be performed under Instrument Flight
Regulations (IFR) which are planned for 2006. The he-
licopter will be flown by two pilots and ACTOS will be
operated by two scientist. This allows measurements
in extensive stratiform cloud sheets which would not be
possible under VFR and which will significantly extend
the capabilities of ACTOS.
3. Measurement Example
The first field campaign with the helicopter-borne AC-
TOS was conducted in April 2005 at the airfield
Koblenz/Winningen, Germany. Here, one example is
shown to illustrate the unique possibilities of using a
slow-flying helicopter-borne payload for cloud investiga-
tions. The data were taken on 27 April at a height of 2100
– 2300 m above ground level. Since the helicopter was
not allowed to penetrate into the cloud, a constant flight
level could not be maintained due to varying cloud top
heights. Figure 3 depicts a 70 s long record of selected
parameters for this flight leg. The with maximum
indicates a cloud penetration close to
cloud top. The vertical velocity shows strong downdrafts
at cloud edges and updrafts with the same order of mag-
nitude in the cloud core region. It is noteworthy that both
Seconds of the day [UTC]
downdraft regions at the cloud edges are still inside the
cloud with a non-vanishing . The temperature de-
creases rapidly when entering the cloud and drops from Figure 3: Measurementsof liquidwatercontent
C. Whereas inside the cloud core the fluctu-
wind velocity , static air temperature , and aerosol particle
are comparable small,
in the size range 6 to 1000 nm (
fluctuations between the cloud regions.
red curve) and 12 to 1000 nm (
, black curve). The true
An interesting feature is contained in the record of the airspeed of the helicopter was 15
aerosol particle number concentration
in the size range between 12 and 1000 nm is relatively
constant over the entire record the second data set in-
cluding the size range from 6 to 1000 nm,
shows sev- 4. Summary
eral significant peaks after the cloud penetrations with
up to four times higher particle concentrations. The oc- The approach of using a helicopter-borne measurement
currence of so-called ultrafine particles in the size range system for cloud research was introduced. The unique
between 6 and 12 nm is an indication for freshly nucle- possibilities and limits of such a system for high resolu-
ated particles. The cloud edges are a preferential region tion measurements were discussed and technical infor-
for new particle formation.
mation of the payload ACTOS were given. A measure-
ment example of a short cloud penetration illustrates the Schmidt, S., K. Lehmann, and M. Wendisch, 2004: Mini-
unique capabilities of the new system for high resolution
mizing instrumental broadening of the drop size distri-
bution with the M-Fast-FSSP. J. Atmos. Oceanic Tech-
nol., 21, 1855–1867.
Acknowledgement We thank R. Maser, H. Franke, and
D. Schell from enviscope GmbH Frankfurt/M, Germany Siebert, H., H. Franke, K. Lehmann, R. Maser, E. W.
for technical support during the experiment. The heli-
Saw, R. A. Shaw, D. Schell, and M. Wendisch,
copter was chartered from Rotorflug GmbH, Friedrichs-
2006a: Probing fine-scale dynamics and microphysics
dorf, Germany and flown by M. Flath.
of clouds with helicopter-borne measurements. Bull.
R. Shaw's participation was part of a sabbatical leave
Am. Meteor. Soc., submitted.
supported by IfT and the U.S. National Science Founda- Siebert, H., K. Lehmann, and M. Wendisch, 2006b: Ob-
tion (grant ATM-0320953). Part of this work was funded
servations of small scale turbulence and energy dis-
by the Deutsche Forschungsgemeinschaft (WE 1900/7-
sipation rates in the cloudy boundary layer. J. Atmos.
Sci., 63, 1451 – 1466.
Siebert, H. and A. Muschinski, 2001: Relevance of
a tuning-fork effect for temperature measurements
with the Gill Solent HS ultrasonic anemometer-
thermometer. J. Atmos. Oceanic Technol., 18, 1367–
Bachalo, W. D. and S. V. Sankar, 1996: Phase Doppler
Particle Analyzer, in: Handbook of Fluid Dynamics (Ed.
R. W. Johnson). CRC Press.
Siebert, H., F. Stratmann, and B. Wehner, 2004:
First observations of increased ultrafine particle num-
Bange, J. and R. Roth, 1999: Helicopter-borne flux mea-
ber concentrations near the inversion of a conti-
surements in the nocturnal boundary layer over land -
nental planetary boundary layer and its relation to
A case study. Boundary-Layer Meteorol., 92, 295–325.
ground-based measuremnts. Geophys. Res. Lett., 31,
Gerber, H., 1991: Direct measurement of suspended
particulate volume concentration and far-infrared ex- Siebert, H., M. Wendisch, T. Conrath, U. Teichmann,
tinction coefficient with a laser-diffraction instrument.
and J. Heintzenberg, 2003: A new tethered balloon-
Appl. Opt., 30, 4824–4831.
borne payload for fine-scale observations in the cloudy
boundary layer. Boundary-Layer Meteorol., 106, 461–
Haman, K. E., S. P. Malinowski, B. D. Stru´s, R. Busen,
and A. Stefko, 2001: Two new types of ultrafast aircraft
thermometer. J. Atmos. Oceanic Technol., 18, 117–
Lehmann, K., H. Siebert, M. Wendisch, and R. Shaw,
2006: Evidence for inertial droplet clustering in weakly
turbulent clouds. Tellus, submitted.
Muschinski, A., R. G. Frehlich, M. L. Jensen, R. Hugo,
A. M. Hoff, F. Eaton, and B. B. Balsley, 2001: Fine-
scale measurements of turbulence in the lower tro-
posphere: An intercomparison between a kite- and
balloon-borne and a helicopter-borne measurement
system. Boundary-Layer Meteorol., 98, 219–250.
DIE VERENGTEN ATEMWEGE Dabei steht die Entzündung der Atemwegsschleimhaut im Mittelpunkt, das führt zur Schwel ung und Schleimabsonderung in den Bronchien. Dadurch kann die Luft beim Ein- und Ausatmen nur erschwert und mit deutlich größerer Kraftanstrengung durch die Atemwege strömen. Die äußeren Zeichen einer solchen Verengung der Atemwege (= obstruktive Bronchitis): • Beschleunigung der Atmung
For BROCK BIOLOGY OF MICROORGANISMS, THIRTEENTH EDITION Michael T. Madigan, John M. Martinko, David A. Stahl, David P. Clark Chapter 26 Microbial Growth Lectures by John ZamoraMiddle Tennessee State University © 2012 Pearson Education, Inc. Microbial Growth Control • Sterilization – The killing or removal of all viable organisms