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AMF2 MAGIC Study of Marine Stratocumulus Clouds in the Northeast Pacific OceanSurface Meteorology QA Summary Based on Leg 03 Time Series

AMF2 MAGIC

R. Michael Reynolds22 Oct 2012, revised 26 Oct

MAGIC SHIPBOARD METEOROLOGICAL SYSTEM

Data Review & QA Based on

Leg03

06 Oct,1132 to 18 Oct,1318 2012

Fri 2012 10 26


This document provides a first review of the data quality for the shipboard ocean-atmospheric-radiation system that was deployed on the M/V HORIZON SPIRIT on 15 Sep 2012. Each of the measurements has been examined for accuracy. The sensor performance is assesed and possible corrections to improve the data set are defined.

Note: This document is part of a work in progress. It is a first look at the meteorological data from the Spirit. We will be improving our analysis as future Legs come in. http://rmrco.com/docs/m1212_MagicMet.pdf

Post processing notes:

1. RAD SW was adjusted by 1.108 due to a calibration difference.

SUMMARY

Fri 2012 10 26
http://rmrco.com/docs/m1212_MagicMet.pdfhttp://rmrco.com/docs/m1212_MagicMet.pdf


The AMF2 was be deployed on the M/V HORIZON SPIRIT.

CALL SIGN: WFLGLENGTH: 272.3 mBREADTH: 30.5 mDISPLACEMENT: 38662 tonne no load 61678 tonne full loadDRAFT: 8.53--12.44 m (no load/load)FUEL: 900 bbl/daySPEED: 20 kt typCARGO HT: 21-17 m approx.BRIDGE DECK HT: 17.7-13.8 mBRIDGE ROOF: 20.4-16.5 mPEAK HT: 33.5-29.6 m (wind monitor)RADAR HT: 29.3-25.4 m (met boom)ISAR HT: 19.2-15.3 mPRP HT: 20.2-16.7 m Note: Heights are above sea level (a.s.l) and vary by 3.9 m depending on ships cargo.

M/V HORIZON SPIRIT

Fri 2012 10 26


ISAR SST

The figure was taken from the Iridium SBD transmissions. The transmissions are sent every half hour but ISAR computes SST every ten minutes. At the end of the leg we recovered all the 10-min data. There was a computer problem in the first hours of the transit. Also, the ISAR GPS data were bad for this leg. Therefore the MET GPS was merged with the ISAR in the following way.

153oW 144oW 135oW 126oW 117oW 21oN

24oN

27oN

30oN

33oN START

o283

o285 o

287

o289

o291

END

magic03, FROM 20121006 (280) 07:00:00.0 TO 20121018 (292) 14:20:00.0

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Fri 2012 10 26


Graph comparing air temperature (blue) and water temperature (red). The SST was bad from the start to day 281.9 approx. The ship was in Hawaii from 285.8 to 286.3. The gaps in the blue trace show when MET computer failures occured.

AIR-SEA TEMPERATURE DIFFERENCE

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27 20121006 (280) 11:32 to 20121018 (292) 13:17now = 20121021, 14:37TEMP: AIR(blue), SEA(red)

YEAR DAY

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ATU

RE

Fri 2012 10 26


A graph of Tair-Tsea shows the episodic behaviour of the air sea difference. From a background value of around -0.7 C spikes of less than a day to as much as -2.5 C occur.

AIR-SEA TEMPERATURE DIFFERENCE

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220121006 (280) 11:32 to 20121018 (292) 13:17now = 20121021, 21:01

TEMP DIFF, wx2.ta isar.ssst

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Fri 2012 10 26


AIR TEMPERATURE INTERCOMPARISON

There were three redundant air temperature measurements. HMP is the Vaisala HMP155 T/RH sensor in an aspirated solar shield. WX1 is the Vaisala WXT on the port end of the boom. WX2 is the WXT sensor at the starboard end.

The above graphs show the the WX2 and HMP measurements were very close (+/-0.2C) but the WX1 temperature is high by approximately +0.32 C. The difference was extremely constant throughout Leg02 and now Leg03. Note that during the day it seems that HMP is effected by solar radiation with an error of up to 0.6 C in midday.We will 1. Use WX2 when available. 2. Use HMP if WX2 is not available. 3. Use (WX1-0.35 C) as a last resort.We expect Tair uncertainty to be +/-0.1.

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Fri 2012 10 26


RELATIVE HUMIDITY INTERCOMPARISON

RH measurements show very good agreement between the two WXT sensors but the HMP RH measurement is high by about 4 percent (middle and right panel).

1. Prefer WX2, WX1, HMP-4 2. No obvious dependency on apparent winds. 3. Strong diurnal variation in HMP, 5% approx.

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Fri 2012 10 26


RH PSYCHROMETER COMPARISON

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psychrometer

wx1

.rh

HMP CORRECTION = 2.0WX1 CORRECTION = 2.0WX2 CORRECTION = 2.0

The psychrometer intercomparisons indicate that the WXT data are low by about 2% and the HMP is high by about 2%.

This does not explain the diurnal variations by the HMP which are probab ly re la ted to the so la r contamination.

WX1 = blue pointsWX2 = red pointsHMP = green points

Fri 2012 10 26


BAROMETRIC PRESSURE

Sea level pressure, SLP = P + 3.5 hPa.WX1 and WX2 pressures track to better than 0.2 hPa stdev.Well look at the odd excursion on day 291. Winds?

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1.5 20121006 (280) 11:32 to 20121018 (292) 13:17now = 20121021, 22:52BP DIFF: WX1WX2

YEAR DAY

BP

hPa

Fri 2012 10 26


SHIP SPEED AND DIRECTION

GPS Speed Over Ground (SOG). The typical cruise speed is about 10.2 m/s (23.3 kts) outbound and 8 m/s (15 kts) returning.

GPS Course Over Ground (COG). The holds to a Rhumb line, constant compass heading, outbound and a great circle path returning. During the time at dock the COG is chaotic.

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Fri 2012 10 26


APPARENT WIND SPEED

We show here apparent wind speed and direction measured from WX1 (boom port) and WX2 (boom starboard). The wind monitor (WM) was on the ship peak and is expected to suffer from flow distortion only minimally. Unlike Leg 02, the WM record was good over a significant fraction of the leg. During the cruise the apparent wind direction was mainly from the bow (-90 to 90 deg). However, even though the ship was moving consistently at 10 m/s in a steady direction, wind speeds varied from >20 m/s to almost calm depending on the true winds and ship speed vector.

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Fri 2012 10 26


APPARENT WIND SPEED (cont.)

During the day 290-292 time period we had strong winds off the starboard bow. The two WXT wind sensors showed significant speed variation as a result of flow distortion. The errors were a result of apparent wind speed and direction since error was near zero when wind directions were directly from the bow. With this plot it is not possible to tell if WX1 is overspeeding due to stream line compression or if WX2 is underspeeding due to sheltering.

In this figure we compare WXT1 and WXT2 with the wind monitor (WM) at the mast peak. WM should have minimal flow distortion. It is however higher than the boom (31.6 vs. 27.3) so we expect the WM speeds to be slightly higher the the boom level. Differences at this height are expected to be small if not negligible. For starboard-bow winds WM < WX2 which indicates streamline compression of WX2 as it sits in front of the mast. And WM > WX1 which indicates sheltering.

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Fri 2012 10 26


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APPARENT WIND DIRECTION

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Alignment of the wind sensors is not easy. We were able to align the wind monitor by holding the vane toward its north (bow) mark and having a helper sight through binoculars from the bow. Therefore, we take the wind monitor (WM) as the reference.

Note we had strong winds from the port bow on day 291. This affected the starboard winds (WX2).

Direction choices: 1. WM, mast top

2a. Winds off the bow: WX1+9 deg. b. Winds off starboard: WX2+5 deg.

Fri 2012 10 26


TRUE WINDS

The true wind algorithm requires the following input:wsa,wda - apparent wind speed and direction. We use the WM sensor at mast peak.sog,cog - from the GPS.hdg - ship heading. We use GPS COG. The navigation data are not available and for this ship at 8-10 m/s the difference will be small.A definite diurnal signal is apparent in true and apparent wind speed.282 284 286 288 290 292

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Fri 2012 10 26


RAIN -- RAIN INTENSITY

The ORG module failed during this leg. We show here the Young siphon rain gauge (left panel) and results from the WXT rain sensors. Rain in this region is sparse and light. The WXT and siphon gauges work very poorly in light rain.

Siphon gauge (left panel) shows a steady decline of tenths of a mm over the leg. This comes from evaporation in the siphon tube. The jump at day 285 is not correlated and is probably false. The jump on day 287.8 is correlated with the rain rates registered by the WXT.

In general, as stated in the Leg02 data report, we are not able to quantitatively describe rainfall, yet.

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RG MAX READING IS 50 MM ACCUM RAIN

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Fri 2012 10 26


SOLAR AND LONGWAVE IRRADIANCE

The RAD module on the PRP provides real time shortwave and longwave irradiance. The record here is reasonable although we do not have any comparison measurements. Well look for an intercomparison during the ships drydock period.

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Note: the shortwave (SW) values have been adjusted by a factor of 1.108 to account for the c o r r e c t P S P c a l i b r a t i o n coefficient. (See mg notes for 26 Oct 2012)

Fri 2012 10 26


SOLAR IRRADIANCE

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W/M2

M. Iqbal in "Physical Climatology for Solar and Wind Energy", 1988, World Scientific, pp. 196-242.

T h e s ho r t wa v e i n s o l a t i o n measured by the, corrected, RAD & PSP (red) is compared to the clear sky insolation from the algor i thm by Iqbal . In the algorithm the parameters used were:Integrated water vapor = 3 cmPressure = 1013 hPaAOD at 380 nm = 0.05AOD at 500 nm = 0.05Ozone layer thk = 0.3 cm

This comparison confirms the data col lect ion t iming and indicates the system calibrations are very nearly correct.

Fri 2012 10 26


SPN

Comparison of PSP (blue) and SPN Total (red).

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1000W/M2

Fri 2012 10 26


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W/M2

Plot of the difference SPN1-PSP during the cruise. The difference is very noisy during the day when the signals are high and offset by about 2-3 W/m^2 at night. The daytime behaviour is likely due to a difference in the instrument time constants in partly cloudy conditions.

Fri 2012 10 26


PITCH AND ROLL

The tilt-compass (TCM) in the PRP enclosure provides a good measure of the mean ship pitch (bow up) and roll (port up). The 1-min standard deviations from the 1-sec samples are a combination of lateral accelerations and tilt and thus provide a qualitative look at how much the ship is moving around. That is wavy vs. calm seas.The examples here show that the ship roll is considerably more than the pitch; an understandble result. During the cruise mean pitch was always very small and the mean roll varied only between -2.0 and 1.5 deg.The stormy time on the return segment, around day 291, was apparent.

We will be comparing these measurements with the SeaNav data on future Legs.

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SUMMARY

wsa: WM or WXT from windward sensor.wda: WM then windward WXT, either WX1+7 or WX2+5 Tair: WX2, (WX1+0.35), HMP shows solar error.RH: WX1 or WX2, (HMP-4%)sog: GPS value.cog: GPS value (When sog

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