This is a summary of my travels in The Netherlands, notes taken at the GCSS Meeting, and summary and conclusions provided by Steve Krueger and Chris Bretherton.
Took the train to transfer point and as I was told it would arrive in 15 minutes, decided to put the bike together. Train arrived before I had a chance to get everything packed, but got everything on the train. I got the bike adjusted and all finalized by the time I arrived in Utrecht.
Then I spent about an hour trying to locate travel information (VVV) but the Utrecht area map they gave me was worth it.
Following the VVV's directions I pedaled to DeBilt. It was only 3 or 4 miles and after asking directions I finally found the hotel and arrived by 10:00 a.m. After a shower I took a nap to 12:30 p.m.
Then I pedaled to KNMI and had lunch at their cafeteria with Aad Van Ulden. Finding everything ready for next week's meeting, I decided to take a ride to help keep awake. Aad had mentioned there was a glider port only 10 km west of DeBilt. I decided to check it out. I found a nice forested area near the airport, but a high barbed wire fence looking much like a military area surrounding it. If it looks military, smells military, it must be military. After riding around 3/4 of the perimeter on some scenic winding bike paths, I finally found an information headquarters. As I suspected it was an airport with glider operations but only for military.
So continuing around the perimeter I headed back only to get into a full downpour. I got out my rain poncho which kept me dry except for my feet. After returning to my room to get dry shoes I pedaled toward Utrecht to find supper.
The prices in my hotel ran about $30 U.S. per meal. I found an Indonesian restaurant whose owner found me a room next door to park my bike. The food was interesting with many tastes I had not experienced. It ranged from mild to very spicy and cost about $30! Pedaled back to hotel, watched a U.S. TV program with Dutch subtitles and after reading went to sleep by 10:30 p.m. I slept through to 9:30 a.m.-- Vollie I slept in!
The only problem I had was the bike trails don't always follow the major roadways. Also, since there are no mountains, I frequently got my directions fouled up. At one point I found myself at Soest about 10 km east of my destination.
After getting help from numerous people (all of whom were very helpful) I finally found the Hilversum Airport. There I met a glider club who were operating a two-winch system plus aerotows. The winching operation was very impressive with light signals and a portable control tower.
I got a ride with an instructor in a ASK 13 for the price of the instructor ($10). After a great launch to approx. 200 m we found a thermal and soared in it to approx. 1200 m. Two other planes were in it, flying closer than I have ever been in a thermal. The instructor continued to ask me to flatten out my bank in turns in the thermals contrary to what I have been taught here. Rolf experienced the same thing flying in Switzerland. I had trouble making coordinated turns at first as it was quite different from the sailplanes I have flown so far. The rudder pedals, in particular, were a pain. As you placed your entire foot into metal frames and had to move your whole leg, instead of just wiggle your toes with your heal fixed in place. It was great ride and I got some great views of the area.
I biked back to DeBilt through some forests and farmland, a pleasant ride.
Then I biked to Altrecht to a pizza place and got a pizza and beer for about $10.
The Dutch seem about as conservative about soaring as they are about biking. All the sailplanes I saw were canvas covered--no glass ships here! Aside for lower maintenance costs the old ships fly slow (approx. 30 kts) and have low sink rates so they can stay in the weak thermals and low cloud bases pretty well.
On biking, besides the standard old style bikes being the norm, no one wears helmets, and they look peculiarly at mine, especially with the mirror. Few wear shorts, but instead standard long pants.
Along the way I passed many small farms; dairy, I believe, judging from the manure smells. Many of the farm homes as well as the homes in town had very nice flower gardens. I passed through another forest area so thick there was no underbrush and cars on the highway were instructed to turn on lights.
After 3.5 hours I found my way to Terlet. The area is a highland area with strong winds, more open land scattered with heather about and smaller trees and bushes.
The gliderport is on top of a ridge. Here was an impressive commercial glider operation comparable to Turf near Phoenix. The difference was Turf operates a fleet of 6 or more tow planes. At Terlet they had a single tow plane, an old 2-place motorized glider, and a fleet of high-performance 2-place and single place glass sailplanes. They were all lined up in six side-by-side rows, with several behind the lead planes like the start to the Indy car race.
The trick was a superwinch that operated six winch lines. A truck hauled the six lines up from the winch like the start to a sulky horse race. The lines were dropped parachutes and weak links attached, then hooked on the planes when they were ready to launch. The planes were individually launched but in rapid succession.
The weak link by the way in a metal contraption holding a piece of metal rated to break upon stressed for a two-place or single-place plane (different metal pieces).
I asked the cost for a flight and since it was 2.5 times what it cost at Hilversum. I decided to pass. I liked the club atmosphere better at Hilversum anyway.
I had my lunch and at 3:00 p.m. started back. The ride back was tiring as the winds picked up to 12 to 15 kts dead on the nose.
Oh, I forgot, on the way out and again on my return I passed a windy meadow area near Ede. There there was a kite convention. There must have been 100 or more kites flying in the area, some huge, some big and many small ones. Some contest maybe? Loads of cars were parked along the roadside. It was the only area I had trouble biking because the bikeways were cluttered with family groups on bikes. Mom, pop, the kids, grandparents, etc. all moving at snail's paces and me without a bell yelling "bike passing on left" again and again. I guess they got the idea.
Finally I broke out of the pack and headed along. I was getting pretty tired toward the end, especially my (sore) END. I decided I didn't want to wait and pay a big price for food besides, so I took a 3km (out and return) side-track and stopped at McDonald's--yes me at McDs! I had 2 fish sandwiches, fries, and a vanilla shake for about $6.50 US. Lots of fat and energy to make up for seven hours of continuous biking! When I stepped outside it was raining, so I had to suit-up. Got back to the hotel and ordered a cheesecake to take to my room.
The I relished in a hot shower and then ate my cheesecake with hot drinks prepared from the hot water faucet. Now I'm pooped and going to bed. Hopefully I won't wake up after an hour of sleep like last night. I read from 11:00 p.m to 11:30 p.m. Hence the reason I feel like sleeping in--All part of the adjustment process.
I particularly enjoyed the old boats along the canals, especially the old working sailboats with huge lee boards that people have converted to homes.
I returned to DeBilt and got charged $6 for my bike on the train. I'll have to fold it and put it in my bag to fool them in future.
I found a message from Bjorn at the hotel, so I know he is about but haven't seen him yet.
After a nap I contacted Bjorn and walked into DeBilt with him to keep him company while he ate (remember it is Monday, my fast day). We found a Ching-Indo restaurant, what ever that means where he had a dish that sounded Indian, but tasted more Chinese.
He was able to rent a standard Dutch ironsides single-speed with a coaster bake for about $19 per week.
We then headed southeast on a cool and drizzly morning. Bjorn wasn't so sure he wanted to do this since he neglected to bring rain gear--to The Netherlands? I told him to wear shorts and loaned him my parka which he never used as it never got beyond light drizzle.
We took to narrow, paved roads south and east of Dricebergen-Rijsenmberg. The road had a canal (like our irrigation canals) running along at least one side, with boats (row boats) in front of most houses. Every so often we encountered a castle, some looking pretty old, others probably 19th century. It was a pretty pastoral landscape with plenty of cousheisa smells.
We finally reached the river a top a dyke that was put in place for flood prevention. Eventually we walked our bikes across the gates of a lock, then along dam gates across the river. We then came to a closed, barred gate.
Now what do we do? We saw no signs that we interpreted as "keep out" getting there. Of course, that doesn't mean there weren't any. I found a call box and pushed the button asking if we could get through? On the other side a recreational park was noted on the map. After some discussion, we in English and the guy on the speaker in Dutch, I gathered we were supposed to put 5 Kl (approx. $3) in some box before he opened it. Couldn't find the box and just as we started to turn back across the dam the gate opened about 3 ft and I walked through. They promptly closed it with me out and Bjorn still inside. Now what? After Bjorn and the voice in the box had an English/Dutch discussion, the gate opened again and he quickly slid through.
Once in the recreation area we began exploring it. I found a sailboat rental place and was tempted to rent one. But they wanted 65 Kl for the afternoon or approx. $40 and it was cool, windy and it looked like it would rain. So we pedaled on to a marina that was closed up and moved some chairs under an overhanging roof and had lunch while it rained.
Our lunch consisted of cheese and bread which I had purchased earlier at DeBilt, some apples from our breakfast, and some pears which I picked up beneath a tree along the road. They were great!
We headed back by way of Wijk bij Duurstede, taking a ferry across the river. From there we took some single-lane paved side roads through Cothen (drove through a windmill), Doorn, and again on side roads to Drieberge-Rijsenburg. We headed north through wooded countryside and bike lanes to Austerlitz, the rough woods to Zeist. Zeist is quite a wealthy looking city. Actually I haven't seen anything run down or close to slums here. But Zeist really stands out. I got a pastry and Bjorn cashed some money and, bucking the wind, we headed back to DeBilt. Ah! a nice hot shower again.
I figure I have ridden over 400 km since Friday. My butt is a bit sore, otherwise OK. Bjorn did well on the single speed and kept with me all the way.
Bjorn overview on entrainment.
Taylor's entrainment hypothesis origin of this model.
Separation boundary "laminar super-layer" - Townsend
Basic lab experiments - Deardorff's Tank experiments - 2 layer fluid - sharing grids. Summarizes selected results from lab exps.
Issue of similarity - lab
Stratocumulus -- how does it differ from lab exps?
Debate of quantitative value of field stratocu obs vs. lab exps.
Recent attempts at synthesis. Breidenthal's work.
Summary
Peter Bechtold
Joao Teixeira Describes ECMWF single column model. Shows prog. eqs. for liquid water and cloud fraction and parameterizations of cloud coverage entrainment rates, dissipation of cloud fraction, etc. Describes Monin-Obukov surface layer implementation. Too many eqs. certainly can't absorb all!
Model is available by writing letter to director request it (ECMWF).
Branko Kosovic
Describes his "nonlinear" subgrid scale scheme. Overcomes deficiencies of linear models.
Nonlinear model has 2 more terms added to standard Smagorinsky closure due to strain rate tensor and rotation rate tensor. Simplest nonlinear scheme that has all rotational properties.
Nonlinear model extracts energy better from the mean flow and also does backscatter.
TKE is a little different between linear and nonlinear SCS schemes but temperature fluxes are identical. Smoke fluxes are slightly different. In TKE budget, largest difference in transport term near the inversion.
Overall nonlinear model has small effect for smoke case but it may be more important in a sheared boundary layer case.
It is not known if coefficients are stability dependent--they may be.
Chin-Hoh Moeng
Effect of cloud top cooling on entrainment rate. She varies downwelling radiative flux 60, 40, 20. Potential temperature flux varies linearly with FR. TKE doesn't vary linearly. Cloud top height or varies with FR.
is approx. linearly proportional to average TKE.
Steve Krueger
Stratocu to trade cu transitions. Showed slides of different cloud regimes over Porto Santo. Discusses his 2D cloud-resolving model and application to transition from solid stratus to cu.
Chris Bretherton
More stratocumulus to cumulus transitions. PM mesoscale cellular convection. Agee (1987) fig. showing regions of MCC.
Explanations of MCC's
Hsu and Sun (1991) 3D with turbulence model doing transports
Chris shows 3D simulation for ASTEX 4 June -- nocturnal based on Porto Santo sounding 500 m . Cloud spacing approx. 50 km controlled by up moist/down dry.
Conclusions:
Andreas Chlond - Max Planck Institute
LES model. Added a single-moment bin model of microphysics. Include radiative effects in droplet growth. Have 12 classes - ice particles 1-64 to simulate contrails. For boundary layer clouds they use a bulk microphysics scheme (Lupkes et al., 1989) this scheme is tested for closed-box type calculations.
Radiation scheme. Use spherical harmonic spatial grid method (low truncations 2?; simplified version of Frank Evans scheme). Solutions obtained using conjugant gradient method? Bounded cascade model to describe spatial distribution of cloud liquid-water. Claims errors of approx. 2% for truncations of 5 to 7.
Dave Lewellen
Shows variation in "A" with . Shows strong sensitivity to . Bulk of smoke fluxes come from reasonable scales even for very coarse . Little sensitivity to sub-grid parameterization once m.
Physical Variations
Smoke cooling varied from 10 varied linearly with was constant.
Absorption coefficient (var. thickness of cooling) falls off as layer deepens, but not too much and nearly constant.
Then he lowered cooling rate (made top of smoke transparent) -- entrainment values dropped sharply, but was flat, and dropped.
Cloud with fixed cooling
Complication of radiation coupled to LWC. Set radiative cooling as in smoke, but otherwise cloud could do its thing. With ; 50 200 m all give same fluxes, etc.
Varied moisture amounts, e.g., Randall-Deardorff criteria and increases to a max. at their point and remains constant after that and cloud fraction goes from 1 to smaller values.
For fully coupled cloud (radiation and cond/evp) higher resolution was need than fixed radiation case. But not a lot of higher resolution.
Rate of rise of smoke top varies with method of calculating buoyancy in equation. Hour-to-hour variations in total smoke flux were very large!
Showed plots for all participants--huge scatter!
"A" values varied greatly from monotone to non-monotone schemes. Variability (hour-to-hour) greater in non-monotone schemes.
Clear differences in smoke topped height between monotone and non-monotone.
Sub-grid contributions to smoke fluxes are consistently small. Horizontal velocity variances agree among monotone schemes, less so for non-monotone. Same with .
Theta flux shows more scatter but sub-grid fluxes are very small compared with total.
Skewness values are more consistent except above inversion where monotone schemes yield small values (near zero) of .
Eddy viscosity (diagnosed) varies quite a bit with MacVean and Bjorn showing a max near inversion while others don't. Reasonable consistency in resolved TKE.
High Vertical Resolution
(4 people)
values smaller. Smoke heights closer. Layer average TKE shows more spread but converging? Total smoke fluxes showed most variation. Radiative cooling still appears to extend one grid point above inversion.
2D Results
Restricted domain results less statistical significance in 2D and 3D. is consistently larger in 3D than 2D. Peter Bechtold did only 1D model.
Bjorn's Summary of Many Experiments
Increased resolution increased entrainment if only. Increase gave about same resolution.
P. Mason - If simulations are correct model suggests what is important is local distribution of . You can't distinguish numerical diffusion from Smagorinsky diffusion by scaling.
Hans Cuijpers
Shows differences in predictions of for smoke case for cases using centered differences and using monotonic schemes.
Shows case where most radiative cooling occurring at smoke top and case where most is within the mixed layer.
Conclusion:
Joan Cuxart
Sensitivity of dry entrainment to turbulent Prandtl number and mixing length in 1D and 3D simulations.
New model code, non-hydrostatic built from grid up. 1D simulation can be tweaked to compared well with LES using in 1D gives better results.
Chris B.
Shows dependence of A.
Macolm again
Shows values of for cases of surface heating and cloud top cooling things fall on line if
ASTEX Lagrangian I and 2 cases
Chris and Peter Duynkerke describe the Lagrangian experiments. Peter - Lagrangian 1 -
Drizzle rate: a lot of scatter about 1 mm/day. Estimates of . Stephan de Roode--Turbulent structure of 1st Lagrangian SST increased 4.5 C in 4 days subsidence 0.5 cm s.
estimated ?
2D simulations of ASTER Lagrangian with HUSCI.
Lagrangian 1 -- Forced with observed subsidence, geostrophic winds SST's. Exhibited a deepening of BL with time and transition to cumulus with a decoupled BL.
At end of simulation cloud fraction remained approx. 100% near top of BL which is an overestimate of cloud cover.
Lagrangian 2 -- Subsidence assumed constant throughout period. Simulation gives a drop in BL height followed by a growth while it was observed to rise steadily. Was it the model or data driving it?
Steve Krueger
2D simulation using the UUCEM.
Lagrangian 1 -- Results comparable to Chris except that cloud fraction was much less than 100%. Shows substantial difference in simulation due to radiation.
Lagrangian 2 -- Steve's results more similar to Chris' than either are to observations.
1D models
Joao Texceira
Lagrangian 1 -- BL depth varied reasonably. Cloud cover not bad. LWP ok earlier on but poor later on. What maintained the cloud was not the stratocu para. but large scale condensation from radiation cooling.
Sensitivity -- Not sensitive to radiation scheme frequency of activation. Small time steps smooth oscillations but cloud disappears.
Lagrangian 2 -- Produces convection immediately and produces stratus cloud similar to Chris and Steve.
Erik van Meijgaard
Single column model for global-wide ECHAM4. Nonlocal diffusion (Troen and Mahrt, 1986; Holtslag and Moeng, 1991. Cloud scheme generally based on Sundqvist's scheme.
Lagrangian 2 -- LWC's predicted much less than observed partly because mass flux scheme very active. Cloud cover looked very good.
Lagrangian 1 -- Cloud base very low. Cloud cover solid stratus early on changed to cu and lower cover later as observed. LWC looks good (at 10 hrs later on it creates too high a cloud. Sensitivity experiments with mass flux scheme. Modified entrainment rate which results in mass flux decreasing with height. Increasing entrainment rates doesn't improve results.
Conclusions
LWC underestimated by standard scheme. Increase of lateral entrainment puts increased RH at low levels, but this is in wrong direction.
Pier Siebsma
Mostly discussion of representativeness of sounding. Diagnosed fractional entrainment;detrainment rates much larger than generally used in GCMs and detrainment is larger than entrainment.
Steve Krueger
Presents Don Lenschow's proposed measurement strategy for entrainment.
WRAP UP
Steve K.
Lagrangian 1 -- Drizzle rates reasonably consistent. Sensible heat fluxes are consistent latent heat fluxes are more variable.
Lagrangian 2 -- Lots of disagreement on cloud fraction. Drizzle rates vary a lot with obs being close to zero. Some models 2-3 mm/day.
ASTEX Lagrangians
First Lagrangian: Cases 1,3 -- General agreement with obs BL structure.
Second Lagrangian: Cases 2,4 -- General agreement with cloud but not cloud evolution. Reasons not clear. Candidates: Initial soundings and spin-up time.
Next steps:
The Smoke Cloud Case Study of the GCSS Boundary Layer Cloud WG
Summary of Results and Ongoing Work from Aug 95 Workshop
Chris Bretherton
Results:
Planned Papers and Future Work
Principal topics to investigate further:
Group agreed to met at Clermont-Ferrand next August.
After the meeting Steve Krueger (on Bjorn's single speed rental) and I took a bike ride to the north. Steve had a hard time with the brisk head winds.
We followed winding back country roads with the usual canals along side. In Westbroek we took pictures of a large operating windmill. Very picturesque. From there we found a recreational lake with many sailboarders on it. Steve wants to get back there to sail Sunday or Monday.
We then followed a bike path around the lake and then back to the hotel.
Bjorn, Steve, the student from Penn State working with John Wyngaard and I went to dinner in DeBilt. Had a good meal and a few real great tasting beers.
