Discussion Summary of CLIMODE PI Meeting, 4-5 November 2004, MIT

A. Notes on Expectations/Needs of CLIMODE PI's

1) Air-Sea Interaction: Recurring needs for mesoscale-resolving SST (or ca. 50 km. Resolution) were mentioned by Samelson/Skyllingstad, for their high resolution atmospheric boundary layer modeling; by Marshall for his Walin-type calculations of water mass transformation; by the wintertime seagoing group who needs near real-time imagery for cruise support/planning; and by Weller, for improved surface fluxes [heat and freshwater]. All expected, or hoped, that K. Kelly would provide daily imagery for microwave SST for CLIMODE. Other expectations were that Kelly would also provide altimeter and scatterometer wind stress products. Edson will be collecting microwave skin temperatures and wind stresses during cruises and it would be desirable for him to make comparison with satellite products. All of these products should be collected and archived for CLIMODE beginning in October 2005, prior to our first cruise.

Enhanced spatial data in the atmospheric boundary layer may require that Edson consider how/when radiosondes will be released, or possibly consider adding a towed atmospheric sounder during wintertime cruises. This sounder is a kite which is towed behind the vessel and samples downward through the boundary layer from its tow height of ca. 300m. Also the issue came up whether or not aircraft are totally out of the question for our intensive winter period in 2007. CLIMODE PI's (Edson and Samelson) will explore this with contacts within NOAA and ONR.

Mixed layer depth: John Marshall brought up the need for mesoscale-resolving Mixed Layer depths for a variety of calculations envisioned [e.g., water mass transformation, lateral induction]. It was not clear that any PI in CLIMODE would be focusing on this. A similar statement can be made for Sea Surface Salinity. One thing CLIMODE needs to do is provide links with ongoing efforts elsewhere, such as the Oleander section and the Mercator group in France. Also discussed was CLIMODE dropping XBTs along cruise tracks and collecting underway SST & SSS. These data could be used to evaluate SSS and ML depth products from other sources. R. Lumpkin will investigate getting XBTs for CLIMODE cruises thru NOAA sources.

Improved air-sea fluxes will benefit all of the PI's and recent calculations by Marshall have shown large differences in water mass transformation switching from NCEP to the WHOI daily climatologies by Yu and Weller.

2) Eddies and Mixing. What field data will be collected to advance the CPT Emelie goals of:

On the former, the SeaSoar/ADCP surveys will provide critical data, but the 75 kHz system on Knorr is not useful in the upper 25m. CLIMODE should consider putting a higher frequency system on the vessel for the winter cruises. This had been discussed at one time and T. Joyce should discuss this further with M. Gregg. Also discover if the microstructure instrument [AMP] being planned for use by Gregg can measure finestructure velocity.

Other relevant measurements include the FILIS and surface drifters. Thorpe Scale calculations could be done from the Moored Profilers by J. Toole and B. Sloyan. Results could be compared to direct turbulence measurements by Gregg, but Knorr needs to sample near 2 Moored Profiler moorings for better comparison.

On the issue of the velocity structure within and below convecting mixed layers, the present plan will give data during the compound spar drift [ASIS/FILIS]. Inertial shear below the Mixed Layer is expected to be modulated by mesoscale variability and by surface forcing. However, numerical models cannot have realistic inertial shear without better time resolution than daily forcing. Can CLIMODE get access to 3-hourly forcing for the planned MIT model calculations?

T. Joyce plans ca. 80 CTD stations on the 2 week February 2006 cruise of the Knorr. He needs to make sure that L. Talley is prepared for this many perhaps additional stations since she is supporting the CTD/water sampling on the winter cruises. These stations will be used to define the cross- and down-stream structure of the Gulf Stream since SeaSoar and XCTD work was scrubbed in the budget reductions.

 

3) Circulation and Subduction. One question which came up is how many profiles of EDW thickness and flow would be available from CLIMODE? The WOCE results reported by Kwon and Riser were based on approximately 150 Argo-type float profiles/month. CLIMODE estimates are as follows: 45/month from the Talley floats, 40/month from the Argo array within the EDW region, 100 profiles/month from the 2 MP moorings of Sloyan, and 400 thickness and flow estimates/month from the Fratantoni bobbers. So we can expect to have about 600 estimates/month of EDW thickness and flow during the 2 year intensive phase of CLIMODE [October 2005 - October 2007].

Can we understand the PV balance of EDW outside of the formation region from the floats? The bobber floats will cover much of the recirculation gyre over the course of CLIMODE. A comparison of thickness/velocity correlations should yield a gyre-scale picture of PV bolus or eddy flux out of the EDW. Within the formation region, floats, hydrography, and the Moored Profiler moorings will give a time-dependent PV input, especially during the winter-spring transition when formation and subduction occur.

Question: If temperature staircases are prevalent below the EDW layer, vertical sampling of profiling floats may need to be altered to detect them. This is an issue that can be addressed by Fratantoni by looking at CTD profiles from the A22 lines through the EDW layer.

4) Modeling:

Can eddy-permitting model output be made available for studies of optimal float and drifter dispersal prior to CLIMODE field deployments? And can the SST fields or their relevant statistics be also available for planning the High Resolution Atmospheric boundary layer calculations? R. Lumpkin will investigate obtaining MICOM and perhaps NRL model output for the CLIMODE region.

Can models provide some planning information on location of mixing "hotspots" to better optimize limited shiptime in our winter cruises? Are we looking at meander troughs for our focus? Or should we also be sampling at other sites for comparison? Issues such as incorporating high resolution temporal forcing into regional and GFD-like models need to address the issue of mixing and inertial shear below the Mixed Layer depth. These have already been raised above.

5) Synthesis: Water Mass Transforation and Subduction was presented by J. Marshall and Young-Oh Kwon. Kwon's calculations suggest about 7 Sv. of mean transformation each year, of which only 4 Sv. subducts. Diabatic processes due to vertical mixing or loss of PV by warm-core rings [which are subsequently cooled] may be able to provide the sink to the subducted EDW. Marshall and colleagues at MIT are looking at revised water mass transformation estimates and have found a reduced transformation from the Speer numbers (10-20 Sv) by a factor of two. Estimates of lateral eddy fluxes can reduce this number by a further 5 Sv. leaving a smaller net subduction of EDW than previously thought, more in line with Kwon's and Smethie's estimates of 4 Sv. We expect CLIMODE to stimulate further calculations along these lines.

Another area for modeling and synthesis is the identification of "case studies" such as a cold air outbreak, to focus CLIMODE's attention of synthesizing observations and model calculations for likely key air-sea processes that will play a role in CLIMODE.

B. Programmatic Needs of CLIMODE:

1) Interaction with CPT Emilie: Presently, some members of our CLIMODE group [Ferrari, Marshall] are participants in the Clivar Process team Emilie. Raf Ferrari would like some CLIMODE observationalists to participate and has extended an invitation to all of our group to attend the November 2004 CPT meeting in Providence. In the future, we will try to schedule our two meetings closer together in time [and space]. There are clear overlapping interests in both groups.

2) Plans for a Bio-Geo-Chem Study of EDW:

Invitations were extended to Scott Doney and Mick Follows to join our CLIMODE PI meeting to tell us about possible interests in a bio-geochemical study of EDW by Jenkins, Doney, Bates, and others, who are interested in the flux of nutrients, and carbon dioxide into the EDW, and removal of the same by lateral and vertical processes. During Follows presentation, it became clear that many of the same processes are common to nutrients and gasses as to heat and salt, with the added factor of biology. We expect that if such an effort develops soon, CLIMODE investigators could be entrained in, for example, adding some relevant sensors to their measurement program and collaborating further with this group. It appears that direct covariance estimates of CO2 flux will be possible from the presently planned, drifting ASIS platform according to Edson.

3) Suggestions for CLIMODE Web Site:

Our beginnings of a web site were discussed and suggestions were made for improving the prototype version. To be added are the following:

CLIMODE has been registered as a "*.org" domain, and these links will be accessible via the web. T. Joyce will see that these are addressed and our prototype website will go "public" before the fall 2004 AGU.

4) Follow-up CLIMODE PI Meetings: A second PI meeting will be held at noon on 15 December at the San Francisco AGU. Attending will be T. Joyce, R. Samelson, D. Fratantoni, and W. Dewar, who attended this meeting, as well as K. Kelly and L. Talley, who did not. Our next regular PI Meeting will be September 2005, probably in Woods Hole.


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