#16 - Climbing up for the clouds

Today we had very clean conditions and the lower atmosphere was predominantly influenced by marine aerosol. After a short shower we took off sharp at 13:51 UTC under cloud-free conditions. At the beginning we flew a short horizontal leg near sea level to Charly 1, followed by a vertical profile up to 8.000 ft to Charly 2, as usual. The CCN concentration was very low and almost constant with increasing altitude. It ranged from 50 to 100 #/cm³ at 0.3 % supersaturation. Afterwards we decided to go for low level cumulus clouds above the sea. But in reality the helicopter had to climb up to about 10.000 ft for these clouds, because they were quit convective and developed so fast, as can be seen in the first figure. At about 14:25 UTC, ACTOS had the first cloud contact and by the means of PICT a mean droplet size of about 35 µm was measured. We had the chance to fly on top and at the edge of this cumulus congestus cloud three times. A shift in droplet sizes to larger values was found. Possible explanations for this effect are (a) growing droplets in a still towering cloud or (b) PICT measured droplets at different cloud heights. During the whole flight no cirrus pertubated the radiation measurements, only a very thin fast disappearing stratocumulus was located at our flight altitude. Then we went for other cumulus clouds, some of them contained clearly smaller droplets of about 25 µm and others also larger ones of about 35 µm in diameter, see second figure. Being quite northward of Barbados over the sea and becoming really tired because of the lack of oxygen at this high altitude, we decided to turn back to Charly 2 and to descend down to 3.000 ft, which was approximately the height of the cloud base. A horizontal leg at 3.000 ft to Charly 1 and also one at 1.500 ft was performed on the way back to the airport under cloud-free conditions. Considering the former leg, a maximum CCN concentration of 250 #/cm³ was determined by the mini-CCNc operating in the scanning mode, see third figure. At the higher supersaturation values we can assume that all the potential CCN are already been activated to cloud droplets.

Now we are done, that was our last scheduled measurement flight of CARRIBA 2011 with the helicopter CFNHG carrying ACTOS and SMART-Helios. Many thanks to all contributors and the people who gave me the opportunity to be a part of this project!

Porpoise dives around cloud base

Today we performed (probably) our second last flight. After the low level leg at a height of 50 m (ACTOS height) above the sea, we started the profile up to 8000 ft (helicopter height). During this time almost all clouds in our measurement area disappeared. Only north of Ragged Point nice cumulus clouds were located above the sea with a cloud top at 6500 ft. So, we decided to chase these clouds. Afterwards, we flew back to our measurement area and investigated conditions around cloud base east of Ragged and Deebles Point. We started with a horizontal leg at a height of 3000 ft, followed by four porpoise flights between 1500 ft and 3000 ft and finished with a horizontal leg at 1500 ft (helicopter height). Before the last leg, the mini CCNC was switched to the scanning mode. We finished the flight with a low level leg above sea heading to the airport.

Flight #14

For the flight today we took off at 13:26 UTC. After profiling the atmosphere up to 8000 ft we directly started with cloud chasing over the ocean on the eastside of Barbados. Due to the large vertical extension of the first cumulus cloud we choose, we had to ascend again until we reached 8500 ft. For this first cloud PICT was measuring cloud droplets with a mean diameters of 40 µm. Outside the cloud at 0.1 % supersaturation the minature-Cloud Nucleation Counter measured an almost constant value of the total CCN number concentration with 40 cm^-3. After circling this cumulus cloud for several minutes we decided to investigate a slightly higher dissapearing shallow alto cumulus cloud layer. The cloud droplets of this cloud layer were smaller with a mean value of about 20 µm detected by PICT.
Afterwards we began to analyze some smaller low level cumuli. In the following we performed some porpoise flights between 1500 ft and 2500 ft. After almost two hours flight time and without breakdown of any measurement instruments we landed at 15:22 UTC. As you can see in the graph, the total number cocentration of the measured CCN did not changed significantly at different altitudes. At 0.3 % supersaturation it was roughly stable at 100 CCN cm^-3.

Very clean clouds

After the dust of the last few days we had some very clean clouds today. PICT measured mean droplet diameters of up to 40 μm (see exapmle on the right) and there were only few CCNs. First we started flying a profile in our measurement area, which was soon cancelled to catch the few clouds above the sea (north of Ragged Point) before they move over land. The cloud base was about 1600 ft high. Afterwards we went back to the measurement area and finished the profile from 8000 ft down to 1000 ft. Meanwhile a lot of nice cumuli were carried with the southeastern wind towards us, which we started chasing then. Moving towards Barbados they grew quite fast. During chasing we got too far north, so we went back to the measurement area, where we catched tinier cumuli. Unfortunately, there was cirrus above us almost all the time. Then cloud chasing was finished and we stayed at about 1600 ft below the clouds so the Mini-CCNC could perform the scan mode. Heading back to the airport we finished with a low level leg.

Growing and towering cumulus

During the weather briefing, we recognized cumulus clouds above the sea. So we decided to catch clouds over the ocean in contrast to the flights of yesterday. After the profile from 180 ft (ACTOS height) to 8000 ft (helicopter height) in our measurement area, only very thin cumulus clouds were below us (see upper picture). Additionally, a slightly increased concentration of aerosols and CCNs was detected in 8000 ft. Thus, we decided to stay there for a 5 minutes long leg. Afterwards, we tried to catch the thin cumulus clouds and recognized growing ones over the island. In the middle of the island, the cumulus clouds towered and their tops were partly separated and drifted eastwards resulting in a compact altostratus layer. That is shown in the lower picture, which also shows a cumulus congestus at the west coast of Barbados including some showers. We catched the thicker cumulus clouds at the east coast of Barbados, while the developed altostratus covered the sky above us. Thus, the radiation measurements were handicapped. On our way back to the airport we found some cumulus clouds, which were not influenced by this layer - but there was cirrus above.

To show you all what Birgit meant with "a full round-trip around the island" here is a screenshot of our GPS tracking of flight 10.

Biomass burning on Barbados

After our contact to probably polluted clouds in the morning we had the chance to sample clouds at the same place in the afternoon.
Again we started with a vertical profile from 200 ft (ACTOS) to about 8000 ft (helicopter) in our measurement area. Since there were no clouds off the east coast we decided to fly to the west coast where a couple of mature cumuli stayed almost the complete day - the ones Birgit already observed in the morning.
On our way there we performed a horizontal leg at 6000 ft and recognized increased aerosol number concentration and CCN concentration probably due to biomass burning (see upper picture with one bigger fire in the north of the island).
Finally, we were able to catch the clouds near the west cost (but over land) and performed several cloud passages at different altitudes with ACTOS inside the cloud and at the very top. It was really amazing to watch these big cumuli growing and disappearing right next to each other. It is a pity that my camera ran out of power just as we reached the first clouds... The lower pictures shows one of my last pictures for today.

Clouds over Bridgetown

Today, we started earlier than usual: take off was already at 9:00 local time. We had almost blue sky above the ocean and only a few scattered clouds above the island. As on the days before, we flew at first a profile from approximately 60 m above sea surface to a height of 8000 ft helicopter height above the ocean. However there were still no clouds around us. We recognized a few small clouds above the northern part of Barbados and started flying there. It took some time to reach this region and the clouds were almost gone when we reached them. But PICT got a few droplets to measure to check if the new setup works better. From the north of the island we recognized that the area around Bridgetown was nearly covered with clouds and asked for permission to fly there.That was approved, thus we followed the west coast down to the area of Bridgetown. Finally we got some more cloud contacts above the city area and at least a chance to check the new settings of PICT. After spending a couple of minutes there the flight time was over and we flew back to the Concorde helipad. From the first quicklook it looks like the cloud was more polluted than those above the sea the last days and was probably influenced by the island (PICT was doing well!). During this flight we made a full round-trip around the island to catch our clouds in the end.

Flight #9

Today we started our measurement flight at 9:45 local. Directly after departure we performed a horizontal leg with ACTOS at 200 ft above sea level heading to our measurement area near Ragged Point. After reaching this area we began to ascent for a vertical profile up to 8000 ft heading north. During the ascent we recognized a field of small cumuli slightly north of our measurement area and we decided to hunt for them.All systems seemed to work well and we were lucky to catch more cumuli on our way back into the intended measurement area. Arriving there, unfortunately, nearly all clouds disappeared so we stopped cloud hunting to focus on aerosols. Therefore, we performed horizontal legs at 3000 ft and 1600 ft (helicopter) and in between a couple of vertical profiles (like porpoise dives) to characterize conditions near cloud base. First quicklooks from the aerosol data point to weaker dust concentrations which can also be verified by the MPI lidar quicklook.

It never rains in April

Again Dust and Clouds

Today the dust layer was still obvious from the lidar plot, but the concentration decreased and it seems to be mixed also into the marine boundary layer. We choose a similar flight pattern as the last days: first a vertical profile up to 8000 ft (helicopter height) followed by a horizontal leg for approximately 20 min within the dust layer. Both were done over the sea without any cloud contact. In general, there were no low clouds above the ocean today, but there were nice cumuli over the island (see the picture below).

Thus we went there and dipped ACTOS into them. Some were really thick up to more than 8000 ft and contained a lot of liquid water. We continued cloud chasing for approximately 40 min in height between 5000 and 6000 ft. Before going back to Concorde helipad we went below cloud level for another short horizontal leg. This layer was obviously influenced by biomass burning, the particle concentrations were relatively high and we could also smell it.

After all, another interesting flight giving probably interesting results about the influence of transported dust on trade wind cumulus clouds.

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....

Showers... - no flight today (2011-04-08)

Overcast conditions and several showers made a safe take-off with ACTOS impossible. Afternoon, there will be a workshop at CIMH and an increased chance of showers is predicted, therefore we canceled all flights for today.

Eagle sees clouds

This is an example of the Eagle data: A cloud "image" at 646 nm wavelength from Deebles Point, and the (uncalibrated) radiance spectra of a cloudy pixel inside the red box (top) and a clear-sky pixel (bottom). Eagle "images" are a bit tricky as their coordinates are not x and y but x and t.

ACTOS & HELIOS

Our continuous all-sky camera at Deebles Point caught this image of the heli with ACTOS and HELIOS yesterday. The fence is that of the MPI station.

First ACTOS flight

Today, we performed the first flight with ACTOS and SMART-Helios. The aim of this flight was to test the setup and to provide data for a comparison with MPI observations. Therefore, all flight activity was off the coast close to Deebles Point with a few low-level flights. Since PICT and the SMPS were both not running we decided to avoid cloud contact and measured profiles from 30 to 2000 m with a special focus on cloud base height. A few legs in 50 m above sea level completed the flight pattern. After a first look into the data, all devices were running without obvious problems.

The picture shows ACTOS passing by the MPI station at Deebles Point in a height of 60 m above sea level.

The Eagle has landed

One of the new instruments in this second part of CARRIBA is the hyperspectral imager Eagle, which we have installed at the MPI research site at Deebles Point. We bought it only very recently, and it seems to operate fine and we'd like to thank MPI Hamburg for providing us with the spot and proper voltage supply. The Eagle will spectrally scan the clouds passing over Deebles Point whenever ACTOS and HELIOS are airborne.

CARRIBA 2.0 (beta)

We are back!
Since April 1st the whole crew (old and new) is back in Barbados.
The instruments are being tested and a dummy flight was performed on April 4th.
Again, the HELIOS dummy was destroyed.
Most instruments seem to work fine, with the exception of the SMPS and Tina's PICT, but support is on the way.
Today we plan to perform the first science flight with ACTOS and HELIOS, we'll keep you posted.