air temperature measurements for meteorology and … · air temperature measurements for...

LIMITLESS POTENTIAL | LIMITLESS OPPORTUNITIES | LIMITLESS IMPACT 1

Air temperature measurements for meteorology and climatology– past, present and future

Giles Harrison

Stephen BurtDepartment of Meteorology

University of Reading

National Physical Laboratory9 December 2014

© E

v-K

2-C

NR

Co

mm

itte

e A

rch

ive

LIMITLESS POTENTIAL | LIMITLESS OPPORTUNITIES | LIMITLESS IMPACT

Agenda

• Early days: defining the problem

• Early sensors

• Basic principles of ‘air temperature’ measurement

• Establishing standard methods in meteorology

• Sensor developments

• Standardising exposure and enclosures

• Present day

• Future methods

2

Part 1

Part 2


Meteorological thermometers –A brief history, 1641 to date

• Florence, 1640s• Little Florentine thermometers

• Early series – Accademia del Cimento network

• London, Royal Society, 1660s• Southwell, Boyle, Hooke and Locke

‒ Manley’s Central England Temperature series (1659)

• Wren and Hooke’s AWS of 1678

• Scales, scales, scales …• Daniel Gabriel Fahrenheit 1686-1736

• Anders Celsius 1701-1744

• Self-registering thermometers – maxand min James Six, 1782

• Sheathed thermometers3

Museo Galileo, Florence

2013

Little Florentine

Thermometer –

from Robert

Boyle, New

Experiments

Touching Cold

(London, 1665)

“ Mr Hook[e] produced a part of his new weather Clock which he had been preparing which was to keep an Account of all the Changes of weather which should happen, namely the Quarters and points in which the wind should blow 2ly the strength of the Wind in that Quarter. 3ly The heat and cold of the Air. 4ly The Gravity and Levity of the Air. 5ly the Dryness and moisture of the Air. 6ly The Quantity of Rain that should fall. 7ly The Quantity of Snow or Hail that shall fall in the winter. 8ly the times of the shining of the Sun. This he was desired to proceed with all to finish he hoped to doe within a month or six weeks. ”

Extract from The Royal Society MS Journal Book, 5 December 1678

Quoted in Invention of the Meteorological Instruments by W E Knowles Middleton: Johns Hopkins Press, Baltimore, 1969 – Chapter VII, Early Meteorographs

Robert Hooke’s Automatic Weather Station (AWS) - 1678


Measuring air temperature:Basic principles

5

• Air is a poor conductor of heat

• Ventilation required to reduce equilibrium timeMedium

• Accuracy, precision, response time, robustness, stability

• Recording method, calibration and scale(s), standardsSensor

• Shortwave (solar, 0-1200 W m-2) and longwave(terrestrial, -100 to +500 W m-2) radiation

• Wetting, ventilation, height above ground, surface typeEnvironment

• Weather forecasting and aviation

• Climatology and climate change, other met. researchRequirements


Thermometer enclosures

• Provide protection from shortwave (solar) and longwave (terrestrial) radiation, and precipitation

• Nominally - uniform representative temperature enclosure

‒BUT – reduced ventilation increased response time

• Standard height above ground surface

• 1.25 m UK/Ireland (up to 2 m snowy climates)

• Many different patterns over time and worldwide

• Double-louvred Stevenson-type screen nearest to a worldwide standard6

Stratfield Mortimer, Berkshire

ST

EP

HE

N B

UR

T


Louvred screens/shelters worldwide …

7

Cannes, France Rothera Base,Antarctica

Asheville, NC, USA

aka‘Cotton Region Shelter’

Uppsala, Sweden

TA

MS

IN G

RA

Y, B

AS

GR

AN

T G

OO

DG

E, N

CD

C

HA

NS

BE

RG

ST

RO

M, U

PP

SA

LA

UN

IVE

RS

ITY

ST

EP

HE

N B

UR

T


An alternative approach …

8

Thatched screen – Hong Kong Observatory

ST

EP

HE

N B

UR

T


Thermometer enclosures– are they really uniform?

9

NOT University of Reading Atmospheric Observatory!S

TE

PH

EN

BU

RT



10

University of Reading Atmospheric Observatory



11

Infrared images 18 September 2014, 1437 and 1439 UTCSolar azimuth 212°, altitude 34°, screen temperature 24°C, global solar rad’n ~ 475 W m-2


Establishing reference methods

12

UK/Ireland conventions• Naturally ventilated Stevenson

screen – wood plastic• ‘Open, representative exposure’,

1.25 m above ground• Liquid-in-Glass (LiG) thermometers electronic sensor/s + logger

• World Meteorological Organization (WMO) spec is 1 min average

• Expected combined precision ± 0.1 degC, accuracy ± 0.2 degC

Isfield, Sussex 16 July 1897


Are louvred screens the final answer?

Naturally-ventilated Stevenson-type screens are not perfect –• Significant lag in light winds

• Appreciable warming in strong sunshine, particularly in light winds

• Differences insignificant for many meteorological applications -important in climate science

13

Lag time L (min) between Topen and Tscrn, for minimum (solid points) and maximum (hollow points) temperatures, as a function of wind speed u2 (m s−1), averaged for the hour centred on the screen temperature maximum or minimum.

Har

riso

n R

G. 2

01

1. L

ag-t

ime

effe

cts

on

a

nat

ura

lly v

enti

late

d la

rge

ther

mo

met

er

scre

en

. Q. J

. R.M

eteo

rol.

Soc.

, d

OI:

10

.10

02

/qj.7

45


Present day: a state of flux• ‘Victorian’ standards +

Automatic Weather Stations (AWS)

• Multiple designs of sensor and radiation screen

‒ About 50% ‘manual’, 50% AWS

Lack of spatial and temporal homogeneity

• Mixed motivation (‘synoptic’ vs ‘climate’)

‒ Land surface temp change ~ 0.05 degC per decade (~ 0.7 degC in 150 years)

• Long-term stability, accuracy and precision hard to achieve

‒ Durability of materials unknown14

Part 2

ST

EP

HE

N B

UR

T


21st century:Alternative methods

• Plastic AWS screens+ Smaller, with PRTs or thermistors

- Efficiency of shielding?

15

ST

EP

HE

N B

UR

T

15

ST

EP

HE

N B

UR

T





• Thin-wire sensors+ Much less sensitive to SW/LW

radiation heating effects

- Extremely fragile

16

University of Reading Atmospheric Observatory

PROTOTYPE THIN WIRE SENSOR

ST

EP

HE

N B

UR

T





• Thin-wire sensors+ Much less sensitive to SW/LW

radiation heating effects

- Extremely fragile

• Aspirated sensors+ Constant ventilation ~ 5-10 m s-1

- Requires constant power supply

• Ubiquitous dataloggers• Highlight sub-daily changes

17


Record comparison - daytime

18

°C

Time UTC



19

°C

Time UTC

°C Max

Stevenson 9.0

Aspirated 7.4

AWS 9.4



20

°C

Time UTC

°C MaxDailyMean

Stevenson 9.0 0.87

Aspirated 7.4 0.83

AWS 9.4 0.93



21

°C

Time UTC

degC

ΔT



22

°C

Time UTC

knotsdegC

u10


Record comparison – diurnal cycle

23

Clear skies, erratic light breeze

Sunny startSunrise 0706

Rapid cloudincrease

Cloudy,breezy with rain


Record comparison – night-time

24

10 min

°C

Uncertainty = √ (εT1)2 + (εT2)2


http://www.ncdc.noaa.gov/crn/#

• Reference ‘climate-quality’ observation network developed, deployed, managed, and maintained by NOAA for the express purpose of detecting the national signal of climate change

• 114 sites Alaska to Hawaii – polar regions to tropical

• A sustainable high-quality network that 50 years from now can with the highest degree of confidence answer the question: How has the climate of the nation changed over the past 50 years?

• Three independent measurements of temperature and precipitation at each site (other elements too)

• Emphasis on continuity of record, well-calibrated (calibrated on an annual basis) and highly accurate observations

• ‘Pristine environments’ expected to be free of development for many decades

27

FUTURESThe US Climate Reference Network USCRN


CA Fallbrook 5 NE, San Diego SU Santa Margarita Ecological Reserve (Old Mine Road Site)33.4 N 117.2 W 1127’

April 30, 2008

• White-painted aspirated solar shield, 12 volt DC-powered fan

• Radiation Error: < 5% under max solar radiation of 1116 W/m2

• Shield temp. range: -50°C to 85°C

• DC fan temp. range: -20°C to 75°C

• DC fan flow: 2750 litres h-1

(~ 750 cm3 s-1)

• Power Requirement: 4.3 W

• Fan speed logged and transmitted hourly

Courtesy NOAA


Instrument detail• Standard set of core sensors – 3 m mast

• Off the shelf, commercially-available sensors selected based on performance, durability, and cost

• Core parameters• Air Temperature: three independent temperature sensors (PRTs) each mounted in a

separate aspirated solar radiation shield: sampling interval 2 sec, 5 minute means

• Precipitation: heated precipitation gauges configured with three vibrating-wires to measure both liquid and solid precipitation, and a wetness sensor to improve upon the gauge's accuracy. Most USCRN stations are also equipped with a tipping bucket gauge

• Solar Radiation and wind speed: required to develop the relationship between air temperature measured at a USCRN station and air temperature measured at nearby or co-located historical stations.

• Most sites include relative humidity, soil moisture and soil temperature

• All have the capability to add supplementary sensors in the future

29


FL Titusville 7 E, NASA Kennedy Space Center (SLF Mid-field Site)28.6 N 80.7 W 10’

May 7, 2005

Courtesy NOAA


Mauna Loa Observatory, HawaiiNOAA Earth Systems Res. Lab., Global Mon. Div.

19.5N 155.6W 11092’September 26, 2005

Courtesy NOAA


SUMMARY• Early days: defining the problem

• Early sensors

• Importance of environment/exposure method

• Establishing reference standards in meteorology

• Sensor developments – thermometer 350+ years

• ‘Air temperature’ – approximated by ‘screen temperature’

• Present day – mix of methods and technologies

• Future methods – US Climate Reference Network

• Aspirated air temperatures - a future reference standard?

32


Royal Meteorological Society meeting

Future measurements for climate monitoringWednesday 18 March 2015, Imperial College, South Kensington, London

33

Time Speaker Title

14:00 Stephen Burt FRMetS, University of Reading Introduction and welcome

14:10 Dr Ian Strangeways FRMetS, TerraData Review of past measurement techniques

14:40 Dr Elizabeth Kent FRMetS, National Oceanography Centre, University of Southampton

Ocean measurements – ships, buoys and floats

15:10 Dr Keri Nicoll, University of Reading Radiosondes

15:40 Refreshment break

16:10 Dr Don Grainger, University of Oxford Satellite measurements

16:40 Steve Colwell FRMetS, British Antarctic Survey The Global Climate Observing System

17:10 Dr Tom Karl, NOAA (via live internet link) The US Climate Reference Network (USCRN)

17:40 Discussion

17:50 Meeting Close Details and registration www.rmets.org


QUESTIONS?

34

Cambridge University Press, 2012, 456 pp,

hardback and paperbackWiley, 2014, 280 pp hardback

air temperature measurements for meteorology and … · air temperature measurements for...

Documents