The IMET data from the Thompson proves to be of excellent quality with a total of 1.48% of the reported values being flagged for potential problems. The rain rate (mm/min) were found to be of extremely poor quality and subsequently not included in the public release. The distribution of flags for the remaining variables is detailed in Table 2.

Table 2: Number of Flags and Percentage Flagged for Each Variable

*Percentage<0.01

Bounds Flag:

There was 1 B-flag assessed to a value of atmospheric radiation of -0.2 W·m^-2 by the preprocessor representing a radiation value of less than 0 W·m^-2. This physically unrealistic negative radiation value is likely the result of the instrument not being tuned to low radiation values.

G-Flag:

Only 1G-flag was assessed to relative humidity by the preprocessor. The DQE felt this value was realistic as it was only 3% lower than the given data trend. The flag was left in place to highlight a value that is greater than four standard deviations from the climatological mean (da Silva et al. 1994).

J-Flag:

Platform speed over ground was assigned 280 J flags on the first day of the second cruise, which contains approximately five hours of data. The data were flat lined at 0 m/sec, so the ship was most likely stationary in port. On the following day the data resumed normal operation.

K-Flags:

Nearly all of the 20,027 suspect data flags (K) assigned to atmospheric pressure (P), earth relative wind direction (DIR), earth relative wind speed (SPD), temperature (T), and atmospheric radiation (RAD) were due to signatures of ship motion in the variables. These discontinuous stair steps in the data, related to a change in platform course, heading, and/or speed should not exist in earth relative data and were subsequently flagged as suspect.

Pressure remained fairly consistent with stair stepping occurring throughout the data sets. There were some stair steps in the pressure data that were a result of either a change in forward speed or direction. These stair steps were associated with approximately a 1/2 millibar (mb) decrease in pressure relative to both the forward speed and direction change of the ship. However, there were some stair steps in the pressure data that were not a result of ship motions. These stair steps were related to the ship relative winds and found to increase pressure approximately 1/2 mb when the platform wind direction was from around 0 degrees and were subsequently flagged with the K-flag.

The earth relative wind direction and earth relative wind speed had stair stepping occurring throughout the data sets. The cause was likely due to flow distortion. Flow distortion is the disturbance of airflow from other objects or instruments upstream from the anemometer. The significance of the stair stepping varied throughout the data set; therefore, the earth relative winds should be used with caution.

Temperature had more specific problems. The first of which was due to radiational heating of the ship. When the platform relative wind speed was low, ~3 m/sec or less, significant increases in temperature were occurring during daylight hours. The second problem was ventilation, which occurred when the platform wind direction was from around 180 degrees. This likely affected the flow of the air prior to reaching the bow-mounted thermometer. In these instances, significant increases in temperature were flagged as cautionary.

Deleted Data:

It was determined by the DQE that the rain rate (mm/min) data not be reported in the public release of the data. The rain rate (mm/min) data were inconsistent with the precipitation amounts, so they were deleted.

Spikes:

Isolated spikes occurred in most of the variables throughout the data. Spikes are a relatively common occurrence with automated data, caused by various factors (e.g. electrical interference, ship movement, etc.). These individual points were assigned the S-flag.

References:

Smith, S.R., C. Harvey, and D.M. Legler, 1996: Handbook of Quality Control