The HOT program makes repeated observations of the physics, biology and chemistry at a site approximately 100 km north of Oahu, Hawaii. Two stations are visited about once a month: Kahe Point (Station 1: 21.34N, 158.27W) and Station ALOHA (Station 2: 22.75N, 158W). Various other stations are made intermittently in support of similar research objectives or mooring deployments.
HOT CTD data are collected using a SeaBird CTD 9-11 Plus with dual sensors at the maximum sampling rate of 24 samples per second (24 Hz). They are screened for errors and processed to 2-dbar averages.
The objective of the physical component of HOT is to describe and understand the ocean climate and variability at a deep-water site in the North Pacific subtropical gyre near Hawaii. This requires a long time series of physical
oceanographic variables, including water mass properties and currents, supporting and complementing the objectives of the biogeochemical component of HOT.
Sensor_Name: Seabird CTD
Project_Campaign: Hawaii Ocean Time series (HOT)
Originating_Center: University of Hawaii
Online_size: 28.697 Mbytes; 634 files
Dataset credit required
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1) Hawaii Ocean Time-series (HOT) (Lukas and Karl)
2) World Ocean Circulation Experiment (WOCE)
(officially ended in 1998)
3) Joint Global Ocean Flux Study (JGOFS)
HOT was initiated and funded through grants from the National Science
Foundation under the auspices of the Joint Global Ocean Flux Study
(JGOFS) and the World Ocean Circulation Experiment (WOCE). The
field phase of these programs has ended, but support from the Ocean
Sciences Division of NSF has enabled continuation of our basic HOT
measurement program until mid-2001. The PO component contributes to
the objectives of the World Climate Research Programme (WCRP) Climate
Variability and Predictability (CLIVAR) Programme by providing
information on interannual to decadal variability of the North
Data transfer to NOAA via the NODC/NCDDC Hawaii Liaison,
Mr.Patrick C. Caldwell.
quality control completed
Each of the (approximately monthly) HOT cruises follows the same basic pattern with some flexibility for ancillary projects to be done after the core sampling has been completed. During transit from Honolulu to the time-series station ALOHA (A Long-term Oligotrophic Habitat Assessment) one weight test is done to between 700 and 1000 m at station 1 off Kahe Point (16 km offshore from the western tip of Oahu, 21 20.6' N, 158 16.4' W, 1500 m water depth). Following the successful winch test, a CTD/rosette cast to 1000 m is conducted. This cast serves as a "shakedown" for the remainder of the cruise, and the functioning of the components of the CTD/rosette system as well as coordination between winch, deck and console operators can be tested. The training of new personnel in activities such as taking meteorological observations, and sampling salinities is also done in this station. The data taken at Kahe Point (station 1) represent an additional time-series of water properties at a near-shore site. Upon arrival at ALOHA (station 2), operations commence with a deep cast (maximum depth approximately 4750 m), 36-hour burst sampling3 of the upper 1000 m at the same location, plus CTD casts to support ancillary JGOFS work of about an extra 12 hours duration. Time permitting, the last CTD cast of the cruise will be a deep cast. On occasion, one cast will be done at station 3 (40 miles north of ALOHA at 23 25' N, 158 W). The second and following casts at station ALOHA are sampled to at least 1000 m depth. Cast 2 is called a "density cast" because water samples are taken at a number of specified density values ranging from [sigma-theta]= 27.37 to the surface with the intent to resolve the profiles of salinity, dissolved oxygen, and nutrients in potential density coordinates Depths sampled during the following casts within the 36-hour burst sampling period are chosen both by the JGOFS group and the WOCE team, who have to ensure that at least one water sample each is taken within the mixed layer, the shallow salinity maximum, the intermediate salinity minimum and the deepest position of the rosette for calibration of the CTD conductivity sensor. If oxygen bottles will be taken from the cast, then the sampling should include at least the mixed layer, oxygen maximum, oxygen minimum and the deepest rosette position for calibration of the CTD oxygen sensor. The second deep cast of the cruise (if there is one) should include sampling of oxygen bottles in at least seven levels appropriate for calibration of the CTD oxygen sensor, i.e. in the oxycline and two more levels below the oxygen minimum, in addition to the four levels mentioned before. The primary objective of the HOT program is to assess variability in the central Pacific Ocean on annual and interannual time scales. One of our most important concerns, therefore, is to ensure that the highest possible precision and accuracy is consistently maintained for all water column chemical measurements. In order to achieve the highest possible data quality, we have instituted a quality-assurance/quality-control program, and have attempted to collect all ancillary information necessary to ensure that our data are not biased by sampling artifacts. Because sampling is over 36 hours, one can average out the effects short-term changes of the depth of density surfaces and the magnitude of hydrographic and nutrient variables (inertial, tidal, and shorter periods).
Directories and files: /data root data directory /woce_sum WOCE-type sum file which gives details on position and parameters taken of each cast and station of each cruise. Filenaming convention: hotccc.sum where ccc is cruise number /ctd CTD data. Filenaming convention: hcccasstt.ctd where ccc is cruise number a is constant ss is station number tt is cast number CTD Data Format Document, January 13, 1992 CTD data are distributed in a format specified by the international WOCE Hydrographic Programme Office (WHPO). This document describes that format. Each station/cast is stored in a separate file. A file's name can be determined by the concatenation of 'h', 2 digit cruise number, 'a', a 2 digit station number, a 2 digit cast number and a file extension of ctd. For ex- ample, HOT-1, station 2, cast 3, would be found in h01a0203.ctd. The cruise and position information for each cast is in the cruise summary file (*.sum). The EXPOCODE, station number and cast number can be used to cross-reference the CTD data files with the cruise summary file. This code allows for the identification of the cruise. It consists of a 4 character NODC country-ship code, a maximum of 8 character cruise number followed by a "/" and leg number. For example, the EXPOCODE for HOT-13 on the R/V Moana Wave would be 31MW013/1. The CTD data file has a fixed record length of 65 characters / record. The first six records of a CTD file contain header information: Record 1: Column Format Item 9-22 a14 EXPOCODE (KA=Kaimalino,WE=Wecoma,MW=Moana Wave) 31-34 a4 WHP station identification 41-42 i2 Month 43-44 i2 Day 45-46 i2 Year FORTRAN FORMAT (8x,a14,8x,a4,6x,3i2) C "%*s %s %*s %s %*s %2d%2d%2d" Record 2: 7-12 a6 Station number 20-22 i3 Cast number 36-40 i5 Number of data records in the file FORTRAN FORMAT (6x,a6,7x,i3,13x,i5) C "%*s %d %*s %d %*s %d" Record 3: 16-21 i6 Instrument number 37-41 f5.2 Sampling rate (hz) FORTRAN FORMAT (15x,i6,15x,f5.2) C "%*s %d %*s %f" Record 4: Headers for data columns (variable labels). Record 5: Unit header for data columns. Record 6: Quality byte designators. All columns requiring a quality byte are underscored by seven asterisks. The remaining records contain CTD data. The order of variables in a record are as follows: pressure, temperature, salinity, oxygen, trans- mission, fluorescence and quality. Missing values are flagged with -99.0. Data Record Format: Column Format Item 1-8 f8.1 Pressure (Decibars) 9-16 f8.4 Temperature (Degrees Celsius, International Temperature Scale of 1990) 17-25 f9.4 Salinity (1978 International Practical Salinity Scale) 26-33 f8.1 Oxygen (micromoles per kilogram) 34-41 f8.3 Transmission (% transmission) 42-49 f8.3 CHLPIG (uG/L) 50-57 i8 Number of observations averaged at this pressure level 58-65 i8 Quality (defined by investigator) ** FORTRAN FORMAT (f8.1, f8.4, f9.4, f8.1, 2f8.3, i8, i8) C "%f %f %f %f %f %f %d %d" ** The quality word is the left-to-right concatenation of required qualityi bytes for the variables measured. They are defined as follows: byte value Definition 1 Not calibrated with water samples. 2 Acceptable measurement. 3 Questionable measurement. 4 Bad measurement. 5 Not reported. 6 Interpolated value. 7 Not assigned for CTD data 8 Not assigned for CTD data 9 Not sampled
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