US CLIVAR High Latitude Surface Flux Working Group
Overall plan (revised as of April):
telecon 1: introductions; defining the problem
telecon 2: user requirements
telecon 3: NWP flux issues
telecon 4: producing turbulent fluxes; in situ observation
First Telecon Notes (March 14, 2008)
Agenda:
● Introductions (and consideration of possible membership gaps)
● Discussion of current challenges with fluxes
● Assessment of working group aims, objectives, and schedule
Aims of the working group are to do what we can to obtain better high latitude fluxes.
Motivation:
Surface fluxes at high latitudes are important for a number of reasons including:
● water mass transformation and meridional overturning circulation in the ocean depend
on surface processes
● global heat budgets are controlled by surface fluxes
● wind energy input to the global ocean is dominated by high latitude exchanges
● CO2 exchange is largest at high latitudes in Southern Ocean
● salinity governs the Southern Ocean upper ocean heat balance, so freshwater matters
as well as heat
● changing open water regions due to changing ice implies significant changes in air-sea
fluxes and in albedo feedbacks
Expectations for the working group:
● define current state of fluxes and requirements for future fluxes. Summarize findings
in a paper (aimed at BAMS).
● run a workshop intended to entrain a broader segment of the community into this
discussion.
● lay the groundwork to push for future field work, reanalysis efforts, data analysis, etc.
that might be needed to resolve current flux challenges.
note: IPY Arctic reanalysis is being planned. Can we prod the directions for that effort?
Working group membership spans a number of interests:
Flux users:
● Sarah Gille (SIO). Southern Ocean processes, upper ocean heat budget
● Lynne Talley (SIO). Mode Water and Intermediate Water transformation
processes.
● Gudrun Magnusdottir (UC Irvine). large scale dynamics; feedback with ocean
and ice
● Kevin Speer (FSU) [at sea for this telecon]. International CLIVAR Southern
Ocean working group. Interests in water mass transformation and upper ocean
heat budgets.
In situ fluxes:
● Will Drennan (RSMAS, U. Miami). Flux measurements from buoys,
platforms, towers, ships, including one north of S. Georgia Islands.
● Dave Carlson. (BAS, IPY). Organizer of big projects; Experience with air-sea
interface, particularly at low-wind end; big view.
Satellite measurements:
● Mark Bourassa (FSU). QuikSCAT scatterometer and gridded products;
comparisons with ship observations; flux modeling, SAMOS program.
● Gary Wick (NOAA, Boulder). SeaFlux project, SST and satellite
determination of
● turbulent air-sea fluxes;
Numerical weather prediction:
● Ross Hoffman (AER). Scatterometer for ocean surface winds and variational
analysis methods (including through ECCO GODAE).
ice:
● Cecilia Bitz (U. Washington). Sea ice in climate system, climate modeling.
Notes no data set characterizes uncertainties.
● Mark Serreze (U. Colorado). Largely satellite reanalysis. Interests in
atmosphere and ocean heat budget. Notes that budgets don't close.
Modeling/observations of turbulent fluxes:
● Chris Fairall (NOAA, Boulder). Measurements from ships, ice, and towers.
Involvement with World Climate Research Program Surface Flux Working
Group, SEAFLUX, and Arctic Sea Ice programs.
Kevin Speer sent e-mailed comments suggesting 4 issues to consider:
1. Producing a relatively high space-time resolution flux data set for some period of
years in the Southern Ocean (open water) is within reach and should be a tangible
goal. (Mark Bourassa has done much of work, he says.) Moisture fluxes remain an
issue.
2. How do we extend this to Arctic, with decreasing ice cover? Do the same methods
work, and does the same satellite coverage apply
3. Flux through sea ice as a function of ice concentration would be useful. Presumably
ice thickness is harder to work with.
4. Can we estimate flux in coastal polynyas (following work by Moore, Renfrew).
We considered potential areas of importance that might not be covered in working group
membership:
● aircraft measurements: covered by Drennan, Fairall
● gas exchange: Fairall, Drennan
● clouds: Fairall (SHEBA used Arctic ice cloud lidar; SEARCH cloud radar)
● radiation: could include satellite cloud radiation retrievals,
satellite perspective using new products; surface observational perspective
from satellite; low clouds are an issue
Sample names suggested: Jennifer Kay, Rachel Pinker, Bill Rossow
Discussion of graphics:
Mark Bourassa's plots of flux product differences:
●
●
●
●
JRA versus ERA-40 show large rms differences
NCEP-1 is a big problem; NCEP-2 also has issues
topgraphy could be an issuesstorms in NCEP; operational products are better
than reanalysis
MB noted high resolution in space and time wold be good
NWP products:
● SURFA working group on surface fluxes (WCRP), numerical experiments
● have obtained operational weather model fields, archived in real time, 4x daily
at ½ degree resolution
● 5-6 operational products all to be archived within a year
● also pointers to archive of buoys and in situ data
● intended as a mechanism for operational centers to improve flux products
● weather centers like to improve operational model (rather than reanalysis)
● more leverage with weather centers if looking at their operational models
blended wind (Eta + QuikSCAT) used for some purpose
high resolution model can be averaged to coarse resolution
realistic errors for satellite data would help
How good are fluxes now? What could be done to improve them?
Grid resolution issues
Applications with ERA-40
storms: everywhere and continuous
Spatial and temporal variability?
1 hour and 10 km from point measurements as validation requirement?
Validation will be a challenge.
● Closure studies (e.g. heat budget closure) can be best choice
● In situ observations: validate at selective points
TAO network: derived fluxes and comparisons
Peter Taylor as contact(?)
TAO has learned a lot (including wind vane issues; etc.)
close to meeting 10 W/m^2 requirement
concern that 2/3 of NDBC buoys have broken sensors
IPY objective: wind and energy observations for observing system
SOOS and SAON (Antarctic and Arctic programs) are in planning on 12 month time
scale
We should aim to contribute to discussion of what to keep from IPY and what to add
Preliminary results will need to be examined
● IPY cruises: some flux oriented; some cloud research
● THORPEX: Barents Sea, tremendous surface flux
SEAFLUX papers coming out soon; could leverage off of these papers
Should we aim to have workshop first and write article afterwards? Or write article now
to combine with IPY? (DC suggested workshop first?)
Defer decision to after initial telecons.
Homework:
Each of us should write a pargraph explaining interests; contribute material for web site
The MJO Working Group web site is a good template with lots of science questions and
information.Second Telecon Notes (April 21, 2008)
On the phone:
Legler, Bitz, Gille, Magnusdottir, Speer, Bourassa, Serreze, Wick, Fairall, Carlson,
Drennan. (not available: Hoffman, Talley)
Agenda:
● Applications
● Accuracy and resolution requirements
● Can applications be used to help validate surface flux estimates?
A number of graphics were made available, and we spent time discussing them.
list of graphics:
Kevin Speer: Fig10.pdf
Cecilia Bitz: Bitz_fig4.pdf
Mark Bourassa: bourassa.pdf
Mark Serreze: fluxes_serreze.pdf (or .ppt)
Gudrun Magnusdottir: telecon2.pdf (pp. 1-2)
Sarah Gille: telecon2.pdf (pp. 3-)
Chris Fairall (slides by Simon deSzoeke, sent after meeting): flux_analysis_slides.ppt
comments on Fairall slides (sent after meeting)
Ship observations: comparing with Woods Hole flux estimates and Bill Large's estimates
good comparisons in equatorial Pacific and Easter Pacific and stratocumulus regions
2 degree resolution versus transects (75-85W, at 20S); N-S transects from 10N to 8S
include sensible, latent, IR, cloud properties
Gille example: Shenfu Dong plotted trends and differences between flux products.
For WHOI flux, some question whether latest flux version was used.
can we get realistic satellite winds,
diurnal cycle, inertial cycle hard to resolve
Kevin Speer: notes need a region of buoyancy gain (or heat gain)
mixed layer heat budget
10 W/m^2
compare solid line (box inverse), dotted (NCEP), diamonds (ERA), dashed (COADS),
dash-dotted (NOC);
assigning errors for fresh-water matters
Chris: reanalysis looks pretty poor.
better on net; cancelling errors
doesn't necessarily help to balance heat and freshwater
Large products and Woods Hole probably better than reanalysis
STG: CLIMODE has advocated ECMWF values with COARE-3 algorithm....
Serreze example: ERA-40 (1979-2001)
ERA-40 + hydrographic data in Arctic, seeking info on seasonality
long-term annual mean (net flux mean)
essentially zero, as expected
broad brush assessment: ERA-40 not bad
but interannual variability, trends not present
desired resolution: 1 degree lat/lon, monthly in time, 10 W/m^2
broad brush not bad, but “devil is in details”
spatial component: Arctic Ocean as a whole OK, but smaller regions ....
temporal issue: monthly means average out a lot of sins
January flux downward into ocean
budget requirement; keep up requirement for horizontal exchanges
horizontal flux bigger in July than January
changing heat flux implies changes in horizontal requirements
SHEBA July 1985: July +100; January -60
JRA reanalysis comparable to ERA-40; take closer look at CERES products
Bitz example: heat budget in CCSM2
net flux into ocean
panel (a) minus (d) mismatch
ocean heat content
Bourassa: more humidity in JRA makes difference
Serreze: barotropic correction for mass imbalance in atmosphere in reanalysis
have to correct for this to use imbalance
Kevin Trenberth has pointed out net mass flux into Arctic if correction not made
diabatic versus adiabatic rearrangements
model output looks better than observations; unclear how to make comparison
Bourassa: working with Shawn Smith;
can measure all data that go into flux algorithm and do bias correction
Serreze: surface flux implies ice thickness changes
net fluxes don't have much to balance
same ocean information
ice thickness change not available
point measurements: point versus grid scale
latent and sensible heat flux: 10 meters from surface
Bourassa: difference in scaling larger than observational error issues
Serreze: precipitation: Arctic precip as flux; need 3 or 4 stations within grid scale to
make robust measurement
strategy: look for grid cell with 20 stations
ask how many stations do I need for stable precipitation estimate---3 or 4 apparently
requires instrumenting 100 square km to death to get a handle on station issues
ice versus no ice: leads show up on satellite images
ice concentration measured
25 km resolution to 6 km resolution differences
MODIS for clear sky for leads
open water versus ice
ice concentration data matters: pretty good for passive microwave
250 m resolution: leads can be open water only briefly
Magnusdottir example:
short time scales: weather scales incluence on ocean over Pacific
signature in surface flux at 45N
weather noise drives ocean; heat flux positive into atmosphere;
transients non-linear; drive changes at surface and influence overturning
improving parameterization: need field campaign with global observations
better assesssment
Bourassa: reanalysis versus operational products
surface data base; now compiling surface fluxes
SURFA compiling fluxes
no documentation: NCDC NOAA Climate Data Center
T-PACS? weather prediction
airborne measurements, ships, radar; no surface fluxes
need improvement in parameterization of flux
Bourassa: tower work is problematic; models good; data are poor
Fairall: winter conditions; lack of data is a problem rather than flux parameterization
Magnusdottir: coupled reanalysis would help;
weather patterns can force ocean;
are fluxes in reanalysis fluxes
can we trust NCEP reanalysis?
NCEP-II versus NCEP-I reanalysis fluxes: performance very similar
Bourassa example: weather noise
transient storms modify multi-year regions in heat
examples: sensitivity
MM5 simulation: 2 strong systems (labeled LC1 and LC2)
high resolution mesoscale model
good boundary layer; tracks of ???
surface latent heat flux; sheared; strong sensitivty to latent heat flux
perturbation in weather influence over region
warm air/cold air influence storm differently
small scale noise over SST or gradient
huge bias by ignoring terms; small scale, short-term variability
asymmetry: long-term mean removed
warm sector: is it more stable than cold sector?
net cooling effect? cold sector has unstable air?
larger area in cold sector
MM5 parameterization
Fairall: polynomial stability—probably OK (Louis bulk flux parameterization)
Magnusdottir (later by e-mail): notes that LC1 is anticyclonically breaking
transient, and LC2 is a cyclonic breaking one, so differences between two events
are not so surprising.
Fairall: STREX field program in 1980s. told fluxes don't matters
where to go from here:
summaries of telecons to be made available
highlight unresolved issues
put documents on password protected web site