Everything you ever wanted to know about weather instruments ... but were afraid to ask PDF
Preview Everything you ever wanted to know about weather instruments ... but were afraid to ask
Everything you ever wanted to know about weather instruments Stephen Burt FRMetS CoCoRaHS webinar, 17 October 2013 CoCoRaHS This presentation is Copyright © Stephen Burt 2013. All rights reserved. Reproduction and distribution is permitted for non- commercial purposes only provided the material is reproduced in its original format. Photographic copyrights remain with the original photographer as shown. www.measuringtheweather.com Your presenter: Stephen Burt • I’m 55, married with two grown-up daughters, and I live in central southern England, about 50 miles west of London • I’ve kept my own weather observations for 42 years, initially with basic instruments, almost fully computerised last 20+ years • I’m Chairman of the largest UK group of amateur observers, the Climatological Observers Link www.colweather.org.uk • I’m a fellow of the Royal Meteorological Society and a Member of the American Meteorological Society and the Irish Meteorological Society • My early working years were with the UK Met Office, then 25 years as a marketing director in the computer industry • In 2012 I published my third book, The Weather Observer’s Handbook (Cambridge University Press) • I’m currently completing a Masters degree (MSc) in meteorology at the University of Reading, UK Topics • Basic principles • Why measure the weather? • Instrument siting and exposure • Measuring precipitation • Measuring air temperature • Measuring humidity and dew point • Measuring barometric pressure • Measuring wind speed and direction • Keeping metadata • Making the most of your observations Why measure the weather? • A global habit • Many different reasons – Input to weather and climate forecasting models – Aviation and transport needs – Climatology and climate change – Statutory records E E T T – Hobby/interest MI M O – Education – 8 to 80 C R N C – And many more! - K 2 - v E AWS on Mt Everest, at 8000 m • Well-kept weather records – by organisations and individuals alike – contribute to scientific evaluation of all types of weather and climate phenomena, on scales from seconds to millennia Audience survey - 1 Q1. Do you make instrumental weather observations yourself currently, or have done so within the last year or two? › Yes 94% › No 6% › No, but made weather observations some years ago If yes to Q1, do you make these weather observations - › as part of your job? 1% › for your own interest or hobby purposes? 91% › both? 8% If yes to Q1, how long have you made weather observations yourself? › less than a year? 24% › More than 1 year? 76% Audience survey - 2 If yes to Q1, do you make instrumental weather observations using - › fully manual instruments (such as a thermometer, raingauge)? 51% › fully automatic instruments – automatic weather station? 6% › a mix of both methods? 43% If yes to Q1, how do you keep your records? › Manually (manuscript, in a logbook or similar) 23% › Mostly or completely on computer (spreadsheet or similar) 44% › A mix of both 33% Q2. Which weather elements are of most interest to you? › Precipitation 56% › Air temperature 10% › Humidity and dew point 3% › Barometric pressure 8% › Wind speed and direction 23% Site and exposure ... the basics • Site – the area or enclosure where the instruments are exposed • Exposure – the manner in which the sensor or sensor housing is exposed to the weather it is measuring – ‘Representative and comparable’ Preferable characteristics Avoid Open and well-exposed - well away from Sheltered locations trees, hedges, buildings and other obstructions Ground-level, on flat ground On sloping ground or in hollows Rooftop sites (except wind, sunshine) Above short grass Artificial surfaces – concrete, tarmac etc Safe and secure access Insecure or unsafe locations • Budget instruments correctly exposed on a good site will give better results than poorly-located expensive instruments Precipitation What are we attempting to measure? • Rain, drizzle, snow, rain/snow mixed, hail – also dew, frost or fog Credit: World Meteorological Organization, Geneva • Highly variable in space and time • Very sensitive to exposure – especially wind effects – Obstructions minimum distance N 2 x their height away O TI A Z NI – But – very open sites may need A G R O some shielding, especially in snowfall L A C GI O • Many different types of gauge OL R O E T E – International and climatic variations M D L R O – Differing standards worldwide W Raingauge intercomparison at Vigna di Valle, Italy Measuring precipitation: daily-read gauges • National standards vary – Rim height US 3-4 feet (90-120 cm), UK/Ireland 1 foot (30 cm) • Round, deep funnel to minimise turbulence and outsplash • Calibrated measuring cylinder – resolution 0.1 mm or 0.01 in • Capacity for at least! 100 year 24 h event – Minimum capacity US 500 mm / 20 in S – Consider siting of gauge – will it flood? H a R o C o C • Time of reading – usually morning, S, E G E R 7-9 a.m. Local Time Y R N E H – Essential for comparability Measuring snowfall • Snow depth – Graduated stick held vertically – Average several readings – Relationship snow depth:water equivalent very variable, average 10-12 : 1, varies 5:1 to 20:1 • Precipitation measurements RT U B N E – Standard rain gauges prone to wind errors - H P E T up to 80 per cent S – Wind shields can help – Recording gauges usually useless in snowfall – except vibrating wire types Nipher and Alter wind shields
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