# Presentation: 568877

## Sea Surface Temperature (SST) Analyses for Climate

**Richard W. Reynolds**
**National Oceanic and Atmospheric Administration**
**National Environmental Satellite, Data & Information Service **
**National Climatic Data Center**
**Asheville, NC**
**E-mail: Richard.W.Reynolds@noaa.gov**

**N**ational **C**limatic **D**ata **C**enter

## Introduction

- Why should we care about SST?
- What are the types of SST data?
- In situ (measured from ships and buoys)
- Satellite
- How are the data distributed?
- How are SST analyses computed?
- What are the SST errors?

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## Climate Change Detection

- Surface Temperature
- Land plus SST
- Marine air temperatures not used because biased & noisier than SST

- Smoothed annual anomalies of global combined land-surface air and sea surface temperatures (oC).

- Vertical axis: 	temperature anomaly
- Horizontal axis: 	time

## SSTs for El Niño and La Niña

- Total
- SST
- oC

- Anomaly
- SST
- Anomaly is
- departure
- from
- normal

## El Niño vs. Normal

- Differences  occur in
- Sea level pressure
- Surface winds *
- Precipitation *
- Sea surface salinity *?
- Sea surface temperature *
- Thermocline depth
- Sea level *

- * Measured by satellite

## Typical January-March Weather Anomalies and Atmospheric Circulation

- Moderate to Strong
- El Niño

- Moderate to Strong
- La Niña

## North Atlantic Oscillation (NAO)

- Positive NAO

- Negative NAO

- More frequent & stronger storms
- Warmer & wetter Europe
- Colder & drier Greenland
- Milder & wetter US East Coast

- Fewer & weaker storms
- Colder & dryer Europe
- Warmer & wetter Greenland
- Colder & dryer US East Coast

- Impact in winter

## In Situ SST Data

**SHIP**: ~1800-present
- Uninsulated bucket (common before WWII)
- Insulated bucket (common after WWII)
- Engine intake (common after WWII, roughly 50%)
- Hull contact (relatively new & rare, most accurate)
**BUOY**: ~1979-present
- Moored (thermistor and hull contact, more accurate)
- Drifter (hull contact)
**Biases (differences between observation & truth)**
- Uninsulated biased cold due to evaporation
- Engine intake biased warm due to engine room

## Decadal In Situ SST Coverage

- Number of months per decade with at least one observation in 2o grid cell
- Range: 0-120
-    Scaled: 0-100%
- In Plot

## Ship Buckets for SSTs

**1.**

- Ship’s wooden bucket, 1891
- Courtesy of Scottish Maritime Museum
- Other buckets
- German metal & leather bucket
- UK Met Office,  black insulated bucket
- UK Met Office Mk II canvas sea bucket

**2.**

- Pictures courtesy of David Parker

## Tropical Moored Buoy Array

- Buoy measures
- Surface wind speed and direction
- Air temperature
- SST
- Ocean temperature with depth
- Data available in real time via satellite

## In Situ & Satellite Analyses1982-present

- In Situ Data (ship & buoy)
- Satellite IR: Advanced Very High Resolution Radiometer (AVHRR)
- Began November 1981
- Satellite microwave: Tropical Rainfall Measuring Mission (TRMM) Microwave Instrument (TMI)
- Began December 1979
- Balance between high coverage of satellite and ground truth of in situ data
**Climatologists Hate Biases**

## Ship & Buoy Data

- Buoy distribution complements ship distribution
- Few observations south of 40oS

- Week of 2-8 January 2000

## Satellite: Infrared (IR) SST Data

- Advantages
- Improved coverage over in situ data
- Multiple channels available to eliminate atmospheric water vapor
- High resolution ~ 4 km
- Problems
- View must be cloud free
- Cold biases with cloud or volcanic aerosol  contamination

## Satellite: AVHRRData

- Missing data due to cloud cover
- Missing daytime data north of 40oN due to orbit of NOAA-14

- Week of 2-8 January 2000

## Satellite: Microwave SST Data

- Advantages
- Improved coverage over in situ data
- Improved coverage over satellite IR data
- Error characteristics different from IR data
- Problems
- View must be precipitation free
- Lower resolution than IR (~50 km vs. ~4 km)
- Wind speed dependent

## Satellite: Microwave TMI Data

- Data limits of 38oS to 38oN due to orbit
- Additional diurnal limits due to time of orbit
- No impact of cloud cover

- Week of 2-8 January 2000

## Comments on Errors (1)

- There are three types of errors
- Sampling
- Random
- Ship			~ 1.3oC
- Buoy			~ 0.5oC
- Day Satellite		~ 0.5oC
- Night Satellite		~ 0.3oC
- Bias: differences between observation & truth
- Satellites can help with
- Sampling & Random errors
- Not biases

## Schematic profiles

**Profile A**: Nighttime  **or** Daytime with moderate to strong winds
**Profile B**: Daytime with light (<3m/s) winds
- T(1) is the surface skin temperature
- IR satellite
- T(2) is the bulk temperature just below the skin
- Buoy
- T(3) is the bulk mixed layer temperature.
- Ship

- Comments on Errors (2)

## SST Analyses

- Optimum interpolation (OI)
- Requires error statistics for data & analyses
- Weights data by distance and relative error
- Best with “lots” of data
- Preliminary bias correction of satellite      on relatively coarse spatial scales

## SST Data and Analysis for 1 Week2-8 January 2000: La Niña

## Objective comparisons

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- Withhold a random 20% of buoy SSTs from analyses
- Define set as buoy IDs ending in 4 or 9
- Use withheld buoy data as independent data
- Compute weekly OI analyses
- WITH & WITHOUT satellite bias correction
- Using different satellite data
- AVHRR only
- TMI only
- and TMI + AVHRR

## Weekly OI Analyses

- OI Analyses use
- AVHRR only
- TMI only
- and TMI + AVHRR
- Upper panel: OI without satellite bias correction
- Lower panel: OI with satellite bias correction
- NOAA-14 biases at end of life: mid 2001

- Vertical axis: 	SST anomaly
- Horizontal axis:	time

## Bias of OI – Independent Buoy Data

- OI Analyses use
- AVHRR only
- TMI only
- and TMI + AVHRR
- Upper panel: OI analyses without satellite bias correction
- Lower panel: OI analysis with satellite bias correction

- Vertical axis: 	SST difference
- Horizontal axis: 	time

## SST Anomaly Movie (1997-1998)

- Jan 5
- 1997

- Sep 5
- 1997

- Apr 30
-  1998

- Dec 30
-  1998

## SST Anomaly Movie (1997-1998)

- Jan 5, 1997

- Sep 5, 1997

- Apr 30,  1998

- Dec 30, 1998

- Jan 5, 1997 - Dec 30, 1998

- By Dave Wuertz

## SummarySatellite SST for Climate

- Satellite data greatly reduces SST sampling and random errors over in situ data alone
- Satellites must be corrected for SST bias errors
- Correction done by use of in situ data
- Because in situ data are relatively sparse,               scales of bias corrections are limited to
- 5o  spatial scales
- Weekly temporal scales

**N**ational **C**limatic **D**ata **C**enter