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Physical Oceanography Division Phone: 305/361-4345

4301 Rickenbacker Cswy Fax: 305/361-4412

Miami, Florida 33149-1097

**April 2008**

**[Cruise Plan -- AX10]{.underline}**

**[Ship Name]{.underline}:** ***M/V HORIZON NAVIGATOR***

**[Project Title]{.underline}:** Atlantic Climate Change Program

Volunteer Observing Ship High Resolution XBT Line AX10

**[Beginning date]{.underline}:** Departing Newark, NJ, 26 April 2008

**[Ending date]{.underline}:** Arriving San Juan, Puerto Rico, estimated
29 April 2008

Sections taken four times per year. Next section scheduled for June
2008.

**[Scientific Ship Riders:]{.underline}** Shaun Dolk, Sommyr Pochan -
NOAA AOML

**[Description of the Scientific Program]{.underline}**

The volunteer ship, ***M/V HORIZON NAVIGATOR***, will be involved in a
study of the upper ocean thermal structure of the subtropical North
Atlantic Ocean within the context of the Atlantic Volunteer Observing
Ship Program. Repeat crossings through the center of the subtropical
gyre, every 3 months, will be conducted with the intent of determining
and monitoring the seasonal-to-interannual variability of the upper
ocean. The upper ocean thermal structure obtained by the ship using the
expendable temperature probes (XBTs) will be used to correlate the
subtropical gyre intensity with atmospheric forcing as well as
determining the heat transport. This particular line along nominally
75^0^ W, designated as AX10, will be used in conjunction with the high
resolution line AX7 that transits from Miami, Florida through the
Straits of Gibraltar (Figure 1). Together, these two lines form a closed
box off the eastern United States, which should allow us to make
stronger statements about the effect of heat flux variability on
atmospheric weather patterns.

![](media/image2.jpeg){width="5.252083333333333in"
height="2.6131944444444444in"}

**Figure 1.** Projected station locations for the VOS/XBT line AX10
(blue circles) and the station locations from a sample track along AX7
(red triangles) taken aboard the M/V MITLA during Feb, 1995. Shading
represents progressively deeper bottom contours: 3000, 4000, 5000, and
5500 m.

**[Implementation]{.underline}**

Sampling along this section (designated AX10) began in 1996 (figure 2)
and meets the WOCE (World Ocean Circulation Experiment) criterion for
high resolution deployment providing temperature profiles every 40 km in
the open ocean and between 10-30 km near boundary currents down to a
depth of about 760 m.

Sampling on this section should be of consistent horizontal spacing of
XBT probes (see below) and a nearly repeating track line for each of the
crossing in order to minimize the differences between sections and the
possible aliasing of horizontal gradients in temperature into time
changes of temperature.

The overall plan for the sampling assuming previous ship tracks and
speeds is as follows:

-   *From Port of departure to Ambrose Tower, 40°27\' N, 73°49\' W:* Set
    up and test XBT launcher as desired. No planned sampling.

-   *From Ambrose Tower near 40°27\' N, 73°49\' W to near 39°25\' N,
    73°24\' W* : Low resolution sampling every 40 km (every 21.6 nm):
    i.e., 4 probes over 120 km deployed approximately every 58 minutes.

-   *From near 39°25\' N, 73°24\' W to near 35°17\' N, 71°49\' W*: High
    resolution sampling every 20 km (10.8 nm): i.e., 24 probes over 480
    km deployed approximately every 29 minutes.

    -   Note this sampling should continue **until** you first see the
        Gulf Stream. The northern edge of the Gulf Stream can be
        estimated by looking at the 15°C isotherm at 150-200m. As soon
        as you see this Temperature at this depth, start shooting every
        15 minutes until the Gulf Stream is completely crossed. The
        southern edge of the Gulf Stream is completely crossed after the
        15°C isotherm deeper than 600m).

-   *From near 35°17\'N, 71°49\'W to near 19°30\'N, 66°1\'W*: Sampling
    every 40 km (21.6 nm): i.e., 47 probes over about 1880 km deployed
    every 58 minutes.

-   *From near 19°30\' N, 66°14\' W to 18°40\' N, 66°1\' W*: Sampling
    every 20 km (10.8 nm): i.e., 3 probes over 60 km deployed every 29
    minutes.

-   *After 18°40\' N* XBT locations will be as follows: 18°40\'N,
    18°35\'N, 18°30\'N, 18°29.4\'N and 18°28.8\'N.

![](media/image3.png){width="5.604166666666667in"
height="5.385416666666667in"}

***Figure 2**: Table of times of all section occupations since the
program began in 1994.*

![](media/image4.png){width="4.436805555555556in"
height="2.873611111111111in"}

![](media/image5.png){width="3.7180555555555554in"
height="2.676388888888889in"}

**Figure 3.** Satellite altimetry-derived surface currents and dynamic
height in the North Atlantic for 12 September 2007.

The time interval between XBT deployments is a function of ship speed.
The above time interval estimates are based on a ship traveling at 22
knots. If the ship is traveling at a different speed it will be
necessary to adjust the launch times (see table 1 as a quick guide). If
the planned cruise track deviates significantly from the outline above
please notify Molly Baringer at 305/361-4345 or 305/710-9240.

![](media/image7.wmf)

If the planned sampling is interrupted for any reason (such as an
autolauncher failure) the procedure will be to drop another probe as
close as possible to the planned drop and continue with the desired
spacing of the XBTs for that section of the cruise track (according to
the above guide). If a serious malfunction of the autolauncher occurs
then manually deploy the XBTs from the stern of the ship using the hand
launcher.

The ship-rider will work as needed around the clock to:

> 1\) check and load the auto-launcher;
>
> 2\) check that the system is logging data correctly;
>
> 3\) keep a log of problems, repeated casts due to suspected XBT errors
> and
>
> weather conditions;
>
> 4\) inform NOAA personnel of any difficulties; and,
>
> 5\) deploy ARGO profiling floats and surface drifting buoys as
> necessary.

No drifters or floats will be deployed during this cruise.

**[Summary]{.underline}**

This high resolution XBT line will require 84 probes plus an anticipated
10% failure rate of 8 probes for each Atlantic crossing. This typically
requires a total of 92 probes per crossing and about 368 probes per
year.

> **[What features we are expecting]{.underline}**:

Numerous XBT sections have been taken in areas similar to the ones to be
taken on this AX10 cruise. Several of the previously taken sections
provide guidance in determining where the XBTs will be dropped. Figure 3
shows the expected currents in the region during the cruise.

##### Figures 4, 5 and 6 show some of the typical sections that show features we will be attempting to sample. The most prominent feature is the deepening of temperature contours (isotherms) marking the Gulf Stream (figure 4). The northern edge or 'wall' of the Gulf Stream (or front) is often demarked by the northernmost position that the 15°C isotherm occurs deeper than 150-200m. Further south of the Gulf Stream this isotherm is typically about 600m (or more) deep. Some investigators use the position that the 15°C isotherm goes deeper than 500m to denote the southern edge of the Gulf Stream.

The Gulf Steam is an unstable jet (or front) that wiggles or meanders
considerably as the current proceeds farther into the Atlantic Ocean. We
will attempt to approximate the exact position of the Gulf Stream from
satellite sea-surface temperature (SST) imagery. Near 70-74°W the Gulf
Stream is thought to meander over a 300 km distance between about 35°N
to 38°N. Occasionally these meanders in the Gulf Stream will pinch off
and form rings of anoma­lously warm (or cold) water that appear to the
north (or south) of the Gulf Stream.

![](media/image8.png){width="5.017361111111111in"
height="3.592361111111111in"}

***Figure 4**.* Temperature section of a typical crossing along AX10
(temperature contours as marked

are in ^0^C). This section was taken aboard the ***M/V CSX HAWAII*** in
March of 2001.

![](media/image9.png){width="4.440277777777778in"
height="3.1791666666666667in"}

***Figure 5.*** Temperature section along AX10 showing a cold core ring
(temperature contours as marked

are in ^0^C). This section was taken aboard the **M/V SEALAND CRUSADER**
in August '99.

One example of a cold ring is shown in figure 5. In this figure starting
at the left hand side that is closest to the coast, the cold water off
the NE United States is seen (blue contours at depth). The abrupt
deepening of many isotherms (constant temper­ature surfaces) of the Gulf
Stream occurs near 36-37°N. Further south, the isotherms rise and fall
again briefly marking the presence of a cold 'core' ring (centered at
about 35°N). A warm core ring can be seen in figure 5 located
approximately 300 km offshore near 38°N. Warm core rings are
characterized by isolated regions of relatively warm water usually at
depth. Often these are "capped" over by water consistent with the local
environment. Optimally we would like to sample the Gulf Stream and any
rings with fine horizontal sampling (15-20 km) while the rest of the
ocean is sampled more coarsely (40 km).

Some other features we are looking for include:

-   ***The pocket of warm water typically found along the axis of the
    Gulf Stream***.

> > Note this is marked by waters warmer than 23°C in figure 4 and
> > greater than 25°C in figure 5. This is primarily an advective
> > feature that marks a long filament of warm waters from the Florida
> > Straits and is seen clearly in SST maps. This feature is
> > occasionally obscured during summer when surface heat creates fairly
> > uniformed warm surface temperatures.

![](media/image10.png){width="4.440277777777778in"
height="3.1791666666666667in"}

***Figure 6.*** Temperature section along AX10 showing a warm core ring
(temperature contours as

marked are in ^0^C). This section was taken aboard the **M/V SEALAND
CRUSADER**

in October '97.

-   ***The large volume of \"18°C\" water south of the Gulf Stream***.
    This water is formed through surface cooling during winter and can
    form very deep layers of homoge­neous properties (over 400m thick).
    Figure 4 shows isotherms extending vertically to the surface with
    uniform (or near uniform) water properties from the surface to more
    than 300 m depths. The presence of this water type (we call it a
    water mass) can still be seen in the summer section, figure 5, when
    the surface is warmer by noting the large distance between the 17°C
    and 19°C isotherms. Note that the volume and specific temperature of
    this \"18°C\" water mass varies substantially as a function of time.
    For example the October 1997 section con­tains a large volume of
    water between 18 to 18.5°C, while the August 1999 section contains
    more water in the 19 to 20°C range.

-   **The shelf-slope front.** Very near the coast, surface cooling and
    advection of cold waters from the north produce very cold water that
    typically follows the edge of the continental shelf where it meets
    the continental slope (where the bottom topography deepens from less
    than 100m to over 500m). In the examples in figure 4, the shelf
    slope front is evident by the cluster of closely spaced isotherms
    39°N that slope downwards towards the coast and bottom topography.
    The slope front is generally coincident with the abrupt change in
    the bottom topography about 200 km from Ambrose Tower. Note that
    this feature and its offshore extension will include vertical
    temperature inversions of as much as 5°C (in 100m) with colder water
    on top of warmer water (figure 4). This is due to the low salinity
    of the coastal waters compensating for the lower temperatures. At
    present we are not measuring the salinity along AXl0. We hope that
    some arguments about the correspondence between temperature and
    salinity from historical coastal data can be used to estimate the
    actual density from temperature alone.

**[High Density Check-out list for the Ship Rider]{.underline}** **[Date
Completed]{.underline}**

***Data to be copied to CD or other means of transportable memory***
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

1\. All XBT data in .BIN, .NDC and electronic XBT drop log sheet.

2\. HistoryAllAttempts.txt -- found at
c:\\ProgramFiles\\AMVERSEAS\\XBT\\ARCHIVE

3\. Cruise webpage summary, cruise report, drifting buoy log sheet and
ARGO float log sheet

***XBT data and HistoryAllAttempts.txt CD to each of the following:***

Molly Baringer \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Robert Roddy \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Qi Yao \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Juan Delgado \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

***Argo deployment information while underway***:

e-mailed to: [**aoml.argo@noaa.gov** and
**robert.j.roddy@noaa.gov**](mailto:aoml.argo@noaa.gov and robert.j.roddy@noaa.gov)
**\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_**

***Drifting buoy deployment information while underway***:

**<shaun.dolk@noaa.gov>** \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

***Cruise webpage summary***. This information goes on the webpage
including number XBTs dropped, drifters/floats deployed, any data
affecting issues. Send an email to each of the following:

Gustavo Goni [**gustavo.goni@noaa.gov**](mailto:gustavo.goni@noaa.gov)
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Molly Baringer
[**molly.baringer@noaa.gov**](mailto:molly.baringer@noaa.gov)
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Qi Yao (XBTs) [**qi.yao@noaa.gov**](mailto:qi.yao@noaa.gov)
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Silvia Garzoli **<silvia.garzoli@noaa.gov>**
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Shaun Dolk [**shaun.dolk@noaa.gov**](mailto:shaun.dolk@noaa.gov)
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Juan Delgado (GTS)
[**juan.delgado@noaa.gov**](mailto:juan.delgado@noaa.gov)
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

***Please email a Cruise Report to Molly Baringer, Silvia Garzoli and
Gustavo Goni stating the following:***

-   XBTs deployed

-   Drifters deployed (ID, date, time, latitude, longitude)

-   Profiling floats deployed (start time, deployment time, latitude,
    longitude)

-   GTS transmission (Real-time, twice a day, problems)

-   Additional equipment, tools, supplies needed

-   Problems

-   Recommendations

-   Other narrative

***At the end of the cruise please send an e-mail to Sommyr Pochan
<sommyr.pochan@noaa.gov> notifying her that cruise is over so that a
thank you note can be forwarded to the captain and crew. List any
special thanks or comments that you would like included in the note.***