WRF and ROMS forecast summary for July 31

7/31/2009 - A fast-moving low pressure system passed through the south central Alaska yesterday evening. This system passage caused a tightening of the pressure gradients in the region of PWS, resulting in winds strengthening to 15-20 knots and becoming more northeasterly. Today and through the weekend the ridge is forecast to build back, and depending on the location of the ridge axis, a tendency towards lighter, more southwesterly winds should be seen. The central Sound eddy, as revealed by HF radar observations, weakened overnight, perhaps in response to the stronger atmospheric wind forcing that developed. ROMS nowcast/forecast surface currents also show a weakening in the eddy circulation in the mean surface currents from the first 24 hours of today's ROMS forecast. Interestingly, the mean from the second 24 hours of the forecast shows a return of the eddy circulation. The tidal range will increase slightly over the next 48 hours. At Valdez, the tidal range will be around 10 feet. High water (5feet) will be at 20AKDT, and low water (-5 feet) at 5AKDT. There were no signficant operational issues today.

CTD data

Hi Everyone

Just a quick note - I've found a few errors (about 6 of nearly 100 total casts) in the position/time metadata of the CTD profiles from serial #4773. I have uploaded the corrected files to the AOOS server. Let me know if you need the exact files. However it will be just as efficient to download the entire dataset again as the files are relatively small. I expect the other CTDs to have minor errors, and I'll work on identifying them and fixing them today.

Mark H

ROMS simulated drifter trajectories at HE and MS

Based on the most recent ROMS forecast, I produced the attached three images, releasing simulated drifters at the HE, and both the east and west sides of the MS. According to ROMS, there are very strong inflows at these locations. The only outflow is through the Knight Island Passage. However, it might be difficult to release drifters there because of the narrow width and the tidal fluctuations. Comments and suggestions are appreciated.

First satellite SST image for PWS during our FE!

It must be the clear weather on Thursday. We have the first satellite image for sea surface temperature (SST) from MODIS. The image is a 24-hour composite, taken from the global blended SST product from my group, see http://sst.jpl.nasa.gov. A lot of gaps with noisy features, mostly due to the patchy clouds I believe. I also attach the daily mean ROMS SST, which shows very encouraging agreement between the two, at least in the eastern side of the sound, where we have most of our data collected during the FE. There are some really cold waters in the western sound and outside the MS where ROMS shows a warm bias there, maybe these are the cold glacier waters that we missed in the model and we don't much in situ data there as well! Comments and suggestions are appreciated.

Data Report for July 31st, 2009

New data as of July 31st, 2009 @ 10 PM AKDT:

• Slocum glider (RU21)
  
• Argosphere (0m): 7/31
• SVP (10m): 7/31
• A boatload of CTD data new and old...

Status of other data:

• SVP (40m): last update to FTP site on 7/27
• Microstar (1m): last update to FTP site on 7/29
• Remus: last update was 7/29
• Thermosalinograph: last update was 7/29 (on the 30th)
  

Proposal to collect more T/S vertical profiles during Sat/Sunday

One of the most challenging task in modeling the PWS circulation is to ensure sufficient fresh-water input into the sound coming from rainfall, rivers, runoff and glaciers. We have been estimating the fresh-water input from rivers and runoff based on the WRF simulated rainfall over land (routing them through the various watersheds to put them back in the right place around the sound). However, the fresh-water inflows from glaciers remain unknown, as a result, not represented in ROMS. Thus, the ROMS simulated salinity is significantly saltier than observed.

In order to quantify the fresh-water input from glaciers, we propose to use the last two days to collect more temperature/salinity vertical profiles along a few selected sections, see blue lines in the image, filling the data gaps and close the salinity budget. The proposed cross-sections include: Valdez arm, sections for Columbia Glacier outflow, and sections for glaciers from the College Fjord.

These sections can be surveyed by ship CTDs, gliders and REMUS AUV.

Thanks for your considerations. We can discuss this at tonight and tomorrow morning's telecons.

Drifter release proposal for Sat/Sunday

By looking at the drifter trajectories during the past two weeks, I have identified a gap in the northern end of the MS, see the red dashed line. By Sat afternoon/evening, it would be great to deploy all the Microstar drifters along this red line, and recover them by Sunday afternoon/evening. After this, we should have the entire PWS covered with various drifters.

According to the ROMS prediction, there is a good possibility that these drifters will be drifted in the northeast direction into the sound.

Thanks for your considerations.