Crowdsourced data for quality control and nowcasting - early studies by Met Norway Mareile Wolff1 with input from Cristian Lussana2 and Thomas Nipen3 Norwegian Meteorological Service 1 observation quality and data processing 2 climate services 3 center for development of weather forecast

Netatmo – low cost weather sensors 22.05.2017

Netatmo @ MET Norway Access to live datastream and archive (2013-current)

Netatmo @ MET Norway Precipitation Number of stations

Netatmo’s temperature Outside temperature sensor (and «shield») has to be protected from rain and needs to be sited within the line of sight of the indoor sensor (to guarantee their connection) close to a window and under a roof. Comparison of MET Norway’s AWS Oslo-Blindern and Netatmo Better agreement during winter months

Netatmo’s temperature «Summer» problems: Higher and later daily maximum mostly because of unsufficient radiation shielding Higher daily minimum temperature during night because of changed long wave radiation budget due to siting. 29.-30.6.2017 26.-27.9.2016

Quality control of Netatmo temperatures Altitude check ± 5 STDEV of neighbouring altitudes Buddy check ± 5 STDEV of neighbouring observations Forecast ensemble check ± 5 ensemble STDEV of ensemble mean Spatial consistency check* Close to the cross-validated field 1 2 3 4 z T * Lussana C. et al.,2010 – Q.J.R. Meteorol. Soc. 136: 1075-1088

Example Feb 20, 2017 12 UTC

Use of Netatmo temperatures Challenge: The 2.5 km model does not resolve the actual topography 2 m Model-topography yr.no distributes temperature forecasts which may be more than 3 ºC off the actual values, even if some postprocessing during inversion situations is already in place Real topography

Use of Netatmo temperatures Model Model + Netatmo (°C)

MET Norway’s observation network Varying impact MET Norway’s observation network Netatmo 30 km 1 km Cities Countryside / cabins No infra-structure 30 km 15 km

Use of Netatmo temperatures Measureable effect: Reducing amount of large errors in wintertime from 15% to 5%

Use of Netatmo temperatures Netatmo Nowcast for Hakadal, a town just outside Oslo, based on 13 Netatmo stations located in and near the town: great improvements of January temperatures

Use of Netatmo temperatures … not so easy to deal with the «summer» problems, larger outliers are easily detected, but smaller biases (probably affecting all sensors) might not get caught by QC: working on further improvements

Netatmo Precipiation …Netatmo sensors don’t measure snow -2°C +5°C

Netatmo Wind …underestimates by a factor of ~3.5. Correlation not too bad

Netatmo humidity Overestimates by 2%. Correlation of 0.98.

Other external and crowdsourced data @MET Norway MET Norway is collecting and quality controlling data from the road authorities-network (some hundreds of stations) We also have an agreement to collect car data from the road- authorities service cars, currently working on establishing data transfer Running tests for the use of stations in Bergen area (school network) Discussing agreement with Volvo to collect temperature data of Volvo- cars in Norway Other external weather stations which are associated to our network (and quality controlled) Precipitation stations of municipalitys/citys (control of sewage system and flood managing) Hydropower companies (no free data, but can be used for assimilation and verification of models) Agricultural meteorological service

Summary Quite effective quality control for temperature data in place Use of temperature observations reduces amount of large errors significantly and generally improves nowcasts for individual locations during winter months Use of summer data more complicated due to large influence of radiation (no shielding and altered long wave radiation budget) Precipitation data only usable in summer (no snow) needs more sophisticated QC (combination with radar) Wind and humidity are severely biased, but still have high correlations An increasing number and variety of crowdsourced data are available and advanced quality control techniques are under development

What do we get at what costs? Data collection IT (and other) Resources Number of stations Diversity of sensors Metadata availa-bility Comment Contract with individual providers (Netatmo) low (only one data format to deal with; no need to motivate contributors) high Lowest IT costs, but highly dependent on provider, high risk for inhomogenities, individual station owners may not be aware of that they provide data Station owners provide data (i.e. WOW) (collection service and database to be maintained and kept attractive) moderate Best possibility to get metadata, lower amount of stations, but higher diversity of sensors Citizens report weather impact (visual observations) (App development and database to be maintained, motivation work to achieve critical amont of observations) Possibility for standardized information (but not too complicated), Data mining highest (under constant adaption, several memberships to be maintained) partly High amount of stations and diversity, needs lots of IT resources

THANK YOU !