Air temperature (degrees C) was measured with the Ship's IMET RM Young sensor (SCS) that was located on the ship's meteorological mast on the bow (14 meters above the sea surface). This signal agreed well with the PMEL RM Young sensor at night (78 % of all 30 minute average night time values agreed +/- 0.3 deg C) but during the day the PMEL sensor typically warmer as it was likely impacted by heating of the ships deck (The PMEL sensor was located on the top of the PMEL AERO van). The ship sensor was used for this data record as it appeared to be more representative of the ambient temperature. There were several occasions of a few hours where there was no available ship (SCS) data, during those times the PMEL RM Young sensor was used in this data record.
The relative humidity (%) reported here was measured with the ship's IMET sensor (SCS). The nighttime ship IMET sensor and the nighttime PMEL RM Young sensor number 2 agreed within 2%RH, 96% of the time, using 30 minute average values of each. The daytime values had less agreement due to the warming of the PMEL sensors as mentioned in the previous section. (The PMEL sensor number 1 was typically 5% higher than the ship's IMET sensor and the PMEL number 2 sensor, since it maxed out at about 105% rh it was deemed to be off in calibration). There were several occasions of a few hours where there were no available ship (SCS) data, during those times the PMEL RM Young sensor (number 2) was used in this data record
Barometric pressure was measured with the Ship's SCS sensor.
Total solar radiation was measured with an Epply Black and White Pyranometer (horizontal surface receiver -180, model 8-48, serial number 12946) and an Epply precision pyranometer (horizontal surface receiver -180, twin hemispheres, model PSP, serial number 133035F3) that were mounted on the top of AERO van. Both instruments were calibrated by The Epply Laboratory on October 11,
1994. There were times when the sampling mast shaded ether or both sensors. There were also times when the ship's mast/bridge shaded the sensors. These "bad" data due to shading have not been edited out of the 30 minute data record. The data reported here are from the model 8-48, serial number 12946 radiometer and are in watts per square meter and are the average value over the 30 minute sampling period.
The reported relative wind is from the Ships SCS IMET sensor, described below. (Unlike the Aerosols99 INDOEX project the PMEL anemometer data are not given, due to a malfunction of that sensor during NAURU). The relative wind was calculated by adding the ships SCS true wind vector to the ships velocity vector. The 30 min average relative wind speed and direction were calculated by taking the 1 minute wind data, separating the vector into the for-aft and beam components, averaging each orthogonal component separately and then recombining the components into a 30 minute average vector. This calculated relative wind agreed well with the measured PMEL relative wind data during periods when the PMEL relative wind data were available. The relative wind vector is given in units of meters per second and in direction from the bow, with wind coming directly on the bow as 0, wind coming from the starboard beam as +90 and wind coming from the port beam as -90 degrees.
Wind Components/Wind Speed/Wind Direction:
True Wind speed and direction were calculated from measurements obtained with the Ships IMET wind sensors. These were mounted on the ship's meteorological sampling mast at the bow. These sensors were used as there were least affected by the alterations in wind from the ship structure. The sensors were located 14 meters above the sea surface. The true North and East components of the wind vector were calculated by subtracting the ships velocity vector (as measured by the PMEL GPS and ship gyro compass) from the measured relative wind. The wind components were then averaged into 30 minute bins and are given as the N and E wind components, in m/s. The true wind vector was calculated from these components and is given as wind speed in m/s and compass direction.
The rainfall rate was measured with a Scientific Technology Inc. ORG-100
Optical Precipitation Intensity Sensor. The instrument was
mounted on the railing of Aero van and was used along with wind direction, wind speed and CN to control the aerosol chemistry
pumps. The dynamic range of the sensor is 0.5 to 1600 mm/h. Spikes in the signal maybe associated with sea spray. The 30 minute
averaged data include all data points. The data are reported in units of mm/hr. (Note: since the data are 30 minute averages, summing
all 48 points for one day and dividing by two will give total precipitation in mm for that day.)
PMEL/UW CN and UFCN measurements:
Aerosol particles were sampled at 18 m above sea level through a heated mast. The mast extended 5 m above the aerosol measurement container and was capped with a rotating cone-shaped inlet nozzle that was positioned into the relative wind. Air was pulled through this 5 cm diameter inlet nozzle at 1 m3 min-1 and down the 20 cm diameter mast. The lower 1.5 m of the mast were heated to dry the aerosol to a relative humidity (RH) of 55%. Fifteen 1.9 cm diameter conductive tubes extending into this heated zone provided air to the various instruments and impactors at flows of 30 l min-1. A theoretical analysis of the collection efficiency of the inlet nozzle (Hinds, 1982) showed that, for the range of non-isokinetic conditions resulting from a factor of two variation in wind speed compared to the isokinetic design speed of 8 m/s and a 30 degree axial deviation, the under- or over-sampling of 14 um particles was less than 10%. Similar calculations for the flow divider at the base of the mast indicated a sampling efficiency for 10 µm particles of about 90%. For smaller particles the sampling efficiencies are closer to 100%. Comparisons of the total particle count (Dp > 3 nm) during intercomparisons with the NCAR C-130 and ACE-1 ground stations agreed to within 20% suggesting minimal loss of particle number in the inlet system (Weber et al., 1999). A similar comparison with the NCAR C-130 during INDOEX showed agreement to within 5%.
One of the fifteen 1.9 cm diameter tubes was used to supply ambient air to TSI 3010 (UW 10381A) and TSI 3025A (PMEL CD0000476028) particle counters. A separate ¼” line was used to supply air from the top of the mast directly to a TSI 3760 (PMEL, CD0000281962) particle counter. The 3760, 3010 and 3025 measure all particles larger than roughly 13, 12 and 3 nm respectively. A regression of the total particle counts from the TSI3010 to the TSI3760 yielded TSI3010=TSI3760*1.02 +39 (R2=0.988). The counts from the three detectors are referred to here as CN>13 (TSI3760), CN>12 (TSI3010), and CN>3 (TSI3025). The total particle counts from each instrument were recorded each minute. The data were filtered to eliminate periods of calibration and instrument malfunction and periods of ship contamination (based on relative wind and high CN counts). The data were also filtered of short duration (less than 15 minute) spikes of high CN concentrations except in the region of Nauru Island. The filtered one minute data were averaged into 30 minute periods centered on the hour and half-hour. The value of –999 was assigned to any 30 minute period without data. The data in 1 minute resolution are available on the PMEL Nauru project web page.
Discrete chlorophyll samples were collected by PMEL every six hours while underway from the ship's clean seawater system. The inlet was near the bow at approximately 4 m depth. Collected samples (530 ml) were immediately filtered, put into 10 ml of 90% acetone, and frozen. The samples were analyzed within 3-4 days onboard ship using a Turner fluorometer. The fluorometer calibration was taken from the standard chlorophyll extractions conducted on the INDOEX cruise.
Continuous measurements (not given):
A Turner 10-AU-005 fluorometer with a flow-cell was used for the underway continuous fluorescence measurements. The data contain large diurnal cycles seen previously in continuous fluorescence measurements in the equatorial Pacific. The ship (CO2 program) fluorometer showed similar results. These diurnal cycles are a function of the measurement technique and do not reflect the actual surface chlorophyll concentration. The continuous measurements also show periods of biological growth on the measurement cell. Consequently the continuous fluorescence measurements are not entered into the cruise data base.
Water from the ship's underway pumping system (4 meter depth, bow intake) was run through the underway auto analyzer system to measure surface nitrate + nitrite concentrations. The instrument samples at 10 minute intervals: seawater, blank, seawater, blank, standard, blank; repeating this sequence each hour. Therefore there is one reading for each half hour interval centered at 5 and 25 minutes after the hour. Data are marked with either a concentration, 0 (indicating below detection limit, generally less than 0.02 micromolar), -99 (when there were no data), or 10 when the concentration was off-scale (greater than 6.3 micromolar). All data reported here are in units of micromoles per liter.
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry