Coordinating and Integrating UV Observations in Svalbard

Georg Hansen & Tove Svendby, NILU, Norway

Boyan Petkov & Vito Vitale, ISAC-CNR, Italy

Piotr Sobolwski, IGFPAS, Poland

Josef Elster, University of South Bohemia, Czech Rep.

Kamil Laska, Masaryk University, Czech Rep.

Acknowledgments

We thank the Research Council of Norway/ Svalbard Science Forum for funding the UV-ICARE project (Project No: 270644/E10) in the frame of the Svalbard Strategic Grant program.

We gratefully acknowledge the work of our colleagues, including station engineers, in gathering long-term data series.

The UV-ICARE project - Continuous interest in the atmospheric

ozone layer and UV doses on the ground: two years with close-to-ozone-hole conditions in the Arctic in the recent decade (2011, 2016) – The ozone story is not over yet!

- Previous inter-comparison activities of existing UV/ozone measurements (Ny-Ålesund, Hornsund, Barentsburg?) were not completed satisfactorily.

- Establishment of new station in Longyearbyen, starting of Brewer measurements in Ny-Ålesund

Geographic position of the stations measuring solar UV irradiance and total ozone at Svalbard.

Revisitation of existing data series since 1990s and inter-

comparison campaign of all current instruments

NILU’s Ozone/UV monitoring instruments

GUV 541 multi-wavelength moderate bandwidth filter instrument:

• Five UV channels (305 nm, 313 nm, 320 nm, 340 nm and 380 nm)

• FWHM ~ 10 nm in UV channels

• Main parameter: UV doses; additionally total O3 column, effective albedo/cloud cover

• Start of measurements: 1995

SAOZ UV/Vis spectrometer:

• Zenith sky observations of 300 – 600 nm spectral range (1 nm resolution) with diode array detector

• derivation of total O3, NO2, O4 and H2O columns based on DOAS approach during periods of SZA 81 – 93°(sunrise, sunset measurements; no measurements during summer and winter)

• Start of measurements: 1991

Dobson spectrometer no. 8:

• calibrated/reliable measurements from 1994 to 2003

Instrumentation at the Dirigibile Station, Ny-Ålesund

UV-RAD radiometer: • measures spectral radiance in 8

channels between 300 to 400 nm

• FWHM ca. 1 nm

• operational since 2008

• Data coverage: since 2008, but with

gaps in 2011 and most of 2013

Brewer spectrometer: • Operational since: 2013

• Calibrated in 2015 in cooperation with

NILU

Polish Polar Station Hornsund

February 1996: Start of measurements of UV-B radiation at the Polish Polar Station,

Hornsund, Svalbard, (77.00N, 15.55E), using Robertson Berger type UV meter.

Operated by Institute of Geophysics, PAS.

Hornsund

New/additional Instrumentation

Since April 2005:

• UVS-AE-T UV Radiometer

• Sunshine duration meter CSD-1

• CM11 Pyranometer

(All instruments from Kipp & Zonen)

Instrumentation and settings

• UVS-E-T radiometer (Kipp & Zonen, Holland)

• EdgeBox V12 Data Logger (EMS, Czechia)

• Sampling interval: 5 s Recording interval: 5 s

Solar UV Radiation Monitoring in Longyearbyen

Operated by: University of South Bohemia in České Budějovice, Czechia

Coordinates: N78.22329°, E15.65895°

Altitude: 7 m a.s.l.

Location: Roof of Julius Payer House, Czech Research Station, Longyearbyen

In operation from: 24 August 2017

Installation of UVS-E-T radiometer Julius Payer House in Longyearbyen

Credits: Norwegian Polar Institute

Total ozone measurements at Ny-Ålesund

• Data series composed of ground-based (since 1991: SAOZ, Dobson, GUV) and satellite data (1979-1991: TOMS-Nimbus 7, -Meteor-3)

• Separate trends before (and including) 1997 and after 1997: -7.0%/decade (annual, 1979-1997) -0.4%/decade (annual, 1998-2015)

• Large seasonal differences: -11.7%/dec. (March-May, 1979-1997) 0.1%/dec. (March-May, 1998-2015) -1.6%/dec. (June-August, 1979-1997) -1.6%/dec. (June-August, 1998-2015)

Time series of monthly mean total ozone (mixed sources)

at Ny-Ålesund 1979–2015 (upper panel); residuals of

months March-October after removal of annual cycle and

trends before and after 1997 (lower panel).

UV measurements and trends Ny-Ålesund

• Annual doses (day 60 – 285):

continuous GUV data, except 2005

• Annual dose trend: -0.8%/decade

(non-significant)

• Large variability in monthly trends:

• Spring equinox: -8.1% /

decade (marked cloud

transmittance reduction: more

clouds?)

• June: -1.7% / decade (cloud

transmittance reduction: less

snow?)

• July: +5.8% / decade (cloud

transmittance increase: less

clouds?)

• September: -2.5% / decade

(cloud transmittance reduction:

less snow?)

Comparison of longest UV time series

Daily erythemal dose time series at Ny-Ålesund (upper panel) and Hornsund (lower panel) as measured with the GUV filter instrument (Ny-Ålesund) and combined Robertson Berger UV meter (1996 – 2004) and UVAE-T Kipp & Zonen radiometer (2004 – 2016) at Hornsund

Dai

ly e

ryth

emal

dos

e

(kJ

m-2

)

0

1

2

3

Years

1995 2000 2005 2010 2015

Dai

ly e

ryth

emal

dos

e

(kJ

m-2

)

0

1

2

3

Ny-Ålesund

Hornsund

Spectral analysis of time series

Prominent features:

- Annual cycle

- Semi-annual cycle: albedo/snow cover?

- 4-monthly cycle: ?

- Separation of long-term and short-term variations for further analysis at a period of 117 days

100 101 102 103 104

AM

PL

ITU

DE

A (

kJ m

-2)

10-4

10-3

10-2

10-1

100

PERIOD (days)

100 101 102 103 10410-4

10-3

10-2

10-1

100

Ny-Ålesund

Hornsund

Long- vs. short-term variations

Long-term variations very similar at the two stations, but larger amplitudes of short-term variations at Hornsund

Dai

ly e

ryth

emal

dose

(kJ

m-2

)

0

1

2

3

Long

per

iod

com

pone

nt (k

J m

-2)

0

1

2

3

Years

1995 2000 2005 2010 2015

Sho

rt pe

riod

com

pone

nt (k

J m

-2)

-2

-1

0

1

Years

1995 2000 2005 2010 2015

Ny-Ålesund Hornsund

Comparison, continued

Very good (mean) correlation between long-term components (but much larger deviations in individual years), obviously less spreading in Ny-Ålesund short-term variations

Daily erythemal dose DN (kJ m

-2) at Ny-Ålesund

0 1 2 3

0

1

2

3

-2 -1 0 1 2-2

-1

0

1

2

0 1 2 3

Da

ily e

ryth

em

al d

ose

DH (

kJ m

-2)

at H

orn

su

nd

0

1

2

3

Measured values Long period component Short period component

DH = 0.06 + 0.95*D

N

R ² = 0.81

DH = 0.03 + 0.99*D

N

R ² = 0.98

Comparison GUV – UV-RAD

• Comparison of two different instruments at the same location: only started

• Very good dynamic agreement between the two instruments, but systematic

offset (higher doses derived from GUV)

• Candidate for explanation: radiation transfer model systematic discrepancy in

effective cloud transmittance

Summary and Outlook

• UV-ICARE - an effort to expand the UV network to all settlements on Svalbard and to coordinate and homogenize the different measurement techniques

• Re-analysis and comparison of existing UV data (ca. 20 years) ongoing

• Negative trend (statistically non-significant) of annual integrated dose since the late 1990s

• Large variability of monthly integrated doses: probably combined effect of ozone recovery, changes in cloudiness, reduced snow cover season, reduced aerosol load

• End of April 2018: inter-comparison campaign in Ny-Ålesund including instruments from all stations with UV measurements