TAO/EPIC Ship Request

Presented by Meghan Cronin
to OAR Fleet Management Committee and OAR reps
(Fred Rossman, Louisa Koch, Beth White, Ken Mooney,...)
via conference call on 2/13/01.

Summary

* The TAO/PACS-EPIC project requests a 3-4 day piggyback on the TAO 95W/110W Ron Brown cruise in FY02 and in FY03.

* Three days are the minimum days required to achieve our science goals.

Figure 1.  EPIC science objectives

I'll begin with a discussion of the EPIC science objectives.

* This figure shows the cover page of the "Science and Implementation Plan for EPIC:   An Eastern Pacific Investigation of Climate Processes in the Coupled Ocean-Atmosphere System".

* The bottom figure shows SST field, with cool (blue color) water off South America and along the equator, and warm waters (represented by reds) north of the equator. As shown in the top cartoon, the meridional structure of the SST field is reflected in the cloud structure: The sratus deck extends from the cool waters off South America to the convective region of the cold tongue / ITCZ complex. At and north of the ITCZ, in the "breeding grounds" of east Pacific tropical storms, SSTs are extremely warm.

* Understanding the ocean-atmosphere coupling responsible for the structure and evolution of the CT/ITZC complex is a prime objective of the EPIC program. It is expected that this will lead to improved predictability of short-term climate analyses in the Pan-American region and improved predictability of warm season rainfall over the Americas.

EPIC is a US CLIVAR initiative. EPIC fieldwork includes short-term intensive process studies embedded within longer-term larger-scale enhanced monitoring. The EPIC2001 process study (which will take place next September) is funded jointly by NOAA and NSF. Longer-term enhanced monitoring projects (such as the TAO/EPIC project) are funded through the NOAA PACS program by NOAA OAR and OGP.

Figure 2.  Area of work

As part of the enhanced monitoring for EPIC, the TAO array has been enhanced with extra sensors and 3 extra buoys which extend the line northward through the monsoonal trough, and add resolution on the northern edge of the cold tongue where the meridional gradients are large.

Small squares are the TAO moorings.
Big Squares are TAO enhanced moorings.
Big Diamonds are new TAO enhanced moorings -- at 3.5N, 10N, and 12N, 95W
The Star is Bob Weller's IMET mooring in the stratus region.

Each of the 10 enhanced TAO moorings carries shortwave and longwave radiometers, a rain gauge, barometric pressure sensor, extra thermistors in the mixed layer, 7 conductivity sensors and 1-2 current meters, in addition to the standard TAO sensors. These enhancements enable us to monitor the air-sea heat, moisture and momentum fluxes, and upper ocean temperature, salinity and horizontal current structure in the cold tongue/ITCZ complex from the stratus deck region at 8S, 95W through the CT/ITCZ complex to the warm pool region at 12N, 95W.

The enhancements began in November 1999. Final recoveries will occur in the Fall 2003, thus providing 3-4 years of data.

* Funding:
The project has 5-years of funding through NOAA OGP.

* Required Shiptime:
As discussed by Paul Freitag, each mooring must be recovered and a new mooring redeployed in its place at 12 month intervals +/- 1 month. A mooring recovery/deployment takes 1 full day. Thus the 3 additional moorings at 3.5N, 10N, and 12N involve at a minimum, 3 additional shipdays annually, which can be piggybacked onto the TAO tender cruise.

However, because of the extra payload associated with these 3 moorings, the work must be done from a class 1 ship. Thus we have requested a minimum of 3 additional days on the Ron Brown TAO cruise.

The fourth day requested was to do a 1-day intercomparison between the buoy and shipboard measurements. Chris Fairall will have a suite of sensors onboard the 95W/110W TAO tender cruise as part of his EPIC enhanced monitoring project. This made the buoy/ship intercomparison partiuclary interesting as we would be able to compare our bulk fluxes to Chris Fairall's direct flux measurements.

* Effects of dropping the project:
We have requested 3-4 days shiptime on the Ron Brown TAO cruise.

The 1-day intercomparison was a cool idea but is not critical to the science objectives of the program. It could be dropped without jeopardizing the program. However, 3 days are critical. Essentially without these 3 days of shiptime, we cannot have these 3 moorings at 12N, 10N, and 3.5N. 3-days per year to maintain the EPIC enhancements is Rock Bottom.

Figure 3.  June 2000 Cold Tongue/ITCZ complex  (from TAO/EPIC data)

This figure shows the 95W mean cross-section for June 2000. Essentially, this is the observed realization of the cartoon on the cover of the science and implementation document that I showed at the start.

Top panel shows the barometric pressure field,
next panels shows shortwave and longwave radiation.
Next panel -- rain. Highest accumulations are at 8N.
Below that -- winds and some of the currents (in blue).
The bottom 3 panels show upper ocean salinity, upper ocean temperature, and the temperature down to 500 m.

Note, this figure is based only on realtime data. During the first deployment year, most of the subsurface currents were not transmitted and therefore are not shown here.

So what is the effect of not having the 3 extra moorings?

Looking at the winds, we see the convergence (and rainfall) associated with the ITCZ between 5N and 10N. Without the 10N and 12N moorings, we would not have data that straddles the ITCZ.

And what about the 3.5N mooring? Certainly, we need this mooring to help resolve the very temperature front on edge of the cold tongue. However what's really curious is that the salinity field is anomalously fresh between 2N and 4N. Thus the salinity gradient changes sign in this region. What is the role of this salinity structure? What causes and maintains these large meridional gradients? How do they affect the coupled system? We need the 3.5N mooring to help resolve these sharp gradients.

Of course, the system varies on a variety of timescales -- interannually associated with ENSO, seasonally, and on even more rapid time scales. A major advantage of moored buoys is that they we can monitor this temporal variability.

Figure 4.  10N 95W time series

This figure shows the time series of the daily averaged realtime data at 10N, 95W. The panels show the variables in the same order as the previous figure -- bp at top, winds in the middle, and the ocean salinity, and temperature at the bottom. Time here ranges from Nov 99 to yesterday.

Clearly, this is a very complicated system, with large spatial and temporal variability.

Figure 5.  EPIC2001

In September 2001, the CT/ITCZ phase of the EPIC2001 process study will take place next to 10N,95W buoy. As shown in this diagram, measurements will be made from a variety of platforms including -- the Ron Brown, the New Horizon, 2 aircraft, and aerosonds.

The TAO/EPIC mooring array provides critical data to this effort to better understand the meridional structure and evolution of the cold tongue/ITCZ complex.

Summary