Evidence of Saharan dust in the marine boundary layer

A typical size distribution of marine aerosol was measured on April the 9^th at the ground-based measurement station at Ragged Point (red). The Aitken and accumulation mode, seperated by the so called Hoppel-minimum can be seen in the Figure. On April the 15^th a Saharan dust layer with a maximum total number concentration at 2-4 km height was situated above the measurement region. Through synoptic scale advection of these Saharan dust to the measurement region since 14/04/2011 and following downmixing of those particles into the boundary layer, the shape of the number size distribution has changed. Compared to the typical measured number concentration in this marine region (red), the entrainment of the Saharan dust causes an increased number concentration (black) and the typical shape of the Hoppel-minimum gets almost lost.

Flight #07 with a lot of cirrus

Today we performed our 7th flight with all systems running well. A Saharian dust layer between 2 and 4 km was indicated by the MPI lidar, therefore we startet our flight pattern ( 13:42 - 15:25 UTC) with a profile and a subsequent level flight in 2.5 km off the East coast to get a scan with the CCNC.

An Aster satellite overpass was scheduled for 10:37 local - unfortunately there were only very tiny cumulus clouds over the water and we decided to chase a few clouds over land. We sampled a lot of droplets but for the whole day the sky was covered with cirrus clouds so a direct comparison of our measurements with the satellite data will be difficult.

Finally, we got a few clouds over the ocean before we came back to Concorde helipad. An example of our quicklook monitor inside the helicopter is shown in the picture. The lower time series shows the liquid water content of a shallow cumulus clouds, the upper one is the uncalibrated temperature value.

From (Saharan) dust till droplet

Today we performed two quite successful measurement flights including a fully functioning PICT! Both flight pattern included a vertical profile up to 8000 ft off the coast near Ragged Point where the dust layer was located. Afterwards a horizontal flight leg was performed to get full aerosol number size distributions and CCN spectra.
Observed CCN concentration lay in the order of 700 per cubic centimeter and the dust was even visible to the naked eye (see picture).
After the leg in 8000 ft we descended and went for cloud chasing. Fortunately, PICT worked very well and recorded lots of drops - even some lucky ones around 55 microns. Thus, last night's work was definitely worth it.

Thanks to Tina - we both edited this post.

Getting a taste of some juicy cumulus clouds

Today gave us the chance to get a first taste of some juicy cumulus clouds with the phase Doppler interferometer (PICT), recently arrived from Michigan Tech thanks to grad student and courier extraordinaire Matt Beals. The flight began at 09:45 local time and after a vertical profile to 6500 feet we dropped low enough to sample the tops of actively growing cumulus clouds at a flight level of approximately 3500 feet. As can be seen in the accompanying photograph, these clouds were covered by a solid cloud layer well above the flight level. Peak liquid water contents in the cumulus clouds were around 2 grams per cubic meter. Cloud tops were sampled for the next 50 minutes, and then we dropped to cloud base at a flight level of approximately 1800 feet to perform a last level flight before heading to the helipad.

Unfortunately the phase Doppler instrument was not functioning properly, so we could not obtain drop size distributions, beyond a general picture of drop diameters between 15 and 35 micrometers. Post-flight tests finally localized the instrument problem to a slight misalignment of the laser, which we were able to correct with the expert advice of our Artium Technologies colleagues, and a lot of patience and alignment help from Tina, Dieter, Holger, and Sylwester. When we finally got home at about 21:45, 12 hours after the flight began, we were all very happy to have reached the point where we can measure nice Doppler bursts and we have every indication that the instrument will work properly on the next flight.

First cloud contact

Today the third measurement flight of this campaign took place. We had two levels of clouds in the morning, one at 1600 ft and one at 8000 ft. This higher layer covered nearly the whole sky, while there were only scattered cumulus clouds below, but significantly more than yesterday. Thus, the conditions for cloud formation were obviously different and we tried to analyze that in detail. Means, we flew a similar pattern as yesterday: starting with a transfer to the open sea followed by a vertical profile from 50 m to 2000 m. In the meantime we reached a nice field of Cumulus clouds below us. We went down to the clouds and passed several of them at a height around 1200 m.

To compare with yesterdays flight we went down below cloud level to 1100 ft. We flew a horizontal leg there for approximately 7 min followed by vertical profiles through the transition layer: between 1100 and 2500 ft. Since there was still flight time left, we flew through some more clouds and this time the second higher cloud layer was almost gone. After another horizontal leg within 2500 ft between clouds we flew back to the airport below cloud base.

Fewer CCNs since the Saharan dust vanished

Yesterday, the helicopter together with ACTOS and SMART-Helios flew profiles and legs over the Atlantic ocean near by the east coast of Barbados in order to measure the dynamical, thermodynamical and microphysical properties of the transition layer (atmospheric layer between marine boundary layer and trade wind inversion) under cloud-free conditions. Also 5 dolphin flights were carried out between 1100 and 2500 ft to analyze the top of marine boundary layer. The miniature-Cloud Condensation Nucleus (CCN) counter on ACTOS as well as the ground-based CCN measurements on Ragged Point showed much less CCN numbers of about 50-100 than on 06.04.2011 (first test flight). During this flight there was a Saharan dust layer with a maximum height of about 3 km (measured by the MPI-lidar on Deebles point) and 200 CCNs were measured.

Good News: SMPS is working!

After horrible hours of installing and deinstalling of any available version of LabView software, we made it to compile and run the SMPS software. Many, many thanks to Thomas!! First test measurements at ground do not show any problems and ACTOS seems to recover from its "spectrometer problem". The picture shows "USER1"-LED running which caused a lot of happiness :). Results from first measurements will follow....