The current budget of

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The current budget of NO

^y

above the Jungfraujoch as derived from IR solar observations

P. Demoulin, E. Mahieu, R. Zander, G. Roland, L. Delbouille, Ch. Servais, Institute of Astrophysics and Geophysics, University of Liège, Belgium

M. de Mazière, M. Van Roozendael Belgian Institute for Space Aer onomy, Brussels INTRODUCTION

This paper reports on an investigation of a series of compounds of the NO

y

family, based on high resolution infrared solar observations made at the ISSJ (International Scientific Station of the Jungfraujoch), Switzerland (46.55°N, 7.99°E, 3580 m a.s.l.). These observations are part of a longterm monitoring effort undertaken by the Liège group since the mid1970s, and integrated more recently as a contribution to the Network for the Detection of Stratospheric Change (NDSC).

Currently, vertical column abundances of over 20 molecules are retrieved from solar spectra recorded under clear sky conditions as regularly as possible, using two high resolution Fourier transform infrared (2 to 15 μηι) spectrometers [1].

The columns are retrieved from the spectra by nonlinear least squares spectral fitting, using the SFIT 1.09c algorithm; a discussion of the retrieval procedure can be found in [2].

NO

y

BUDGET

NOy, the total reactive nitrogen, is defined as the sum of the following species: NO + NO2 + NO3 + 2(N

2

0

5

) + HNO3 + HO2NO2 + CIONO2 + BrON0

2

. For the purpose of deriving the NOy column trend above the Jungfraujoch, monthly mean columns of those species that can easily be measured from the ground, i.e. NO, NO2, HNO3 and CIONO2, have been calculated from the consistent database spanning from 1985 to present. This procedure of computing monthly means avoids giving excessive weight to months with highdensity observations.

These mean columns are shown as dots in frames A to D of Figure 1; they have been modeled with linear+sinusoidal functions (continuous curves). Trend values, referred to 1990.0, are also indicated with their 1 σ deviations.

The sum of these monthly mean columns, displayed in Figure 1, frame E, represents the most important part of the total NO

y

as derived from the ISSJ data. The missing NO3, N2O5, HO2NO2 and BrONÛ2, not easily observable from the ground, represent less than 5 % of the total NOy [3]

As for the individual species, the NO

y

trend has been simulated with a linear+sinusoidal function (continuous curve); the resulting trend of (0.3 ± 0.3) % per year, although barely significant, is consistent with the trend of (0.35 ± 0.04) % per year, found for the NO

^y

gas source N

2

0 [4] (Figure 2, frame F). The important uncertainty in the NO

y

trend is mainly due to the high variability of the HNO3 columns, which is predominant during the November to April months (circulation and heterogeneous processes).

Notice that the constituents considered in the present investigation show seasonal variations summarized in the following table:

Peaktopeak variation (%) Occurrence of maximum Occurrence of minimum

NO 34 JuneJuly

January

NO2 74 JuneJuly

January

HNO3 28 Feb.March

August

ClONO,

37 March

September

427

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1984 1986 1988 1990 1992 1994 1996

O

Ζ

\f\A/\A/\/\^^

(+0.2 ± 0.2) %/yr

O Ζ

(+0.7 ±0.3]¡ %/yr

22 20 18 16 14 12 10

I I

■ (0.1 ± 0.4) %/yr

•

A A A A

**1 \ ! \ f \ ·Τ*\**

\ / \ /* \ I \ / ' 1

— \I \J

■ • 1

• 1

•

• Λ ι _\

/ · V .

• .

• •

1

·.

• • ·

*

• •

**\ # V */\**

• \ ƒ i \ Π Τ

Λ "Γ· ι / \

\ *m : \·/ * \ w β * ι

•

/* \

•

ι

■

•

. * · -

J \ 7 M / · *

• 1 ~i - \ Ί · -ι ƒ ■ ι J ·

i / \ / - . · ! ·*

• ι

o

ζ

g υ

1984 1986 1988 1990 1992 1994 1996

1984 1986 1988 1990 1992 1994 1996

d F

1984 1986 1988 1990 1992 1994 1996

Figure 1: column abundances above ISSJ, expressed in IO15 molec/cm2

428

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HN0

3

AND HF COLUMNS CORRELATION.

In Figure 2, we have correlated the HNO3 columns with those of HF (with the HF trend removed and reported to 1990.0) obtained on same days. Most of the points cluster about an oblique line: the points on the left correspond to typical summer conditions, whereas those to the right, generally correspond to air masses originating from the higher latitudes, enriched in both HF and HNO3, as a consequence of the latters' latitudinal distribution.

2.2

2.Ü

1.8

1.6

1.4 1.2 1.0 0.8 0.6

1 Γ

Apr.UX A p r 1 5

: \ \

Ì2 o E

■α c

>

u. Χ

Ι

Apr. 21

Linear fit (HF = A 1985

1986 1987 1988

= 0.48 + 0.30 H N O A

O 1989 1990 1991 1992

M*

•

m

=0.39) 1993 1994 1995 1996 1997

1.0 1.2 1.4 1.6 1.8 2.0 2.2

HNOj vertical column abundance (in 10 molec/cm ) Figure 2: HNO3 and HF columns correlation

An interesting episode in March April 1996 is identified in Fig.2 by arrows and dates;

during that period, extremely high values of HF (the highest ever recorded above ISSJ) have been observed.

At the end of March, the polar vortex was centered over Scandinavia and was still well defined. Switzerland was near the edge of the vortex (on the 31

^st

March, potential vorticity was 40xl0"

6

Km

2

kg''s'' at the 475 Κ level). Air masses above the Jungfraujoch originated from the polar regions and were thus enriched in HF; Figure 3 shows an example of back trajectories for the 29

^th

March 1996, ending at the closest rawinsonde station (Payerne, 85 km NorthWest of the Jungfraujoch). The vortex then slowly dissolved: by midApril, only two fragments remained, one centered over East Siberia, the other over Central Europe. Potential vorticity reached again high values (38x10"

⁶

Km

²

kg''s'' at the 475 Κ level on the 18

^th

April) above the Jungfraujoch.

During that time period, no specially high values of HNO3 were observed, as we could have expected from the usual relationship between HF and HNO3 shown in Figure 2: based on the latter, we should have measure HNO3 values around 5xl0

¹⁶

molec/cm

²

instead of the values around 1.5xl0

¹⁶

molec/cm

²

actually observed. This suggests that denitrification occurred in these air parcels.

429

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ECMWF Trajectories

ID days analyses Plotttd al NILU by Iraiplo

O Eid loc: pa,« r u Cid daw: 29.nar.1996 Lca«I : too k O Cid loc: p a , ι rit

Eia d a k : 29.uar.l996 I t a t i : 4T6 κ Λ e ιΰ loc : pa ,» rit

Bid d a n : 29.Har.1996 Ltt-tl : 66D Κ Q E id loc: paft rit

Eld d I H : Z9.Mai.1996 I t a t i :6TS k

Figure 3: back trajectories ending at Páyeme, on the 29' March, 1996

ACKNOWLEDGMENTS

Acknowledgment is made for the financial contributions from the Belgian organizations FNRS and OSTC, Brussels. We thank J. Granville, O. Hennen (IASB) and R. Blomme (KSB) who participated in some observational campaigns at ISSJ. We further thank the Stiftungsrat of the Jungfraujoch and the University of Liège for supporting the facilities needed to perform both the observations and their analysis.

REFERENCES

1. Delbouille L. and G. Roland, High-resolution solar and atmospheric spectroscopy from the Jungfraujoch high- altitude station, Optical Eng., 34, 2736-2739,1995.

2. Rinsland C.P. et al., C10N02 total vertical column abundances above the Jungfraujoch Station, 1986-1994:

Long-term trend and winter-spring enhancements, J. Geophys. Res., 101, 3891-3899,1996.

3. Wetzel G. et al., Nitrogen partitioning inside the 1997 late winter Arctic vortex, derived from MIPAS-B limb emission measurements, this volume.

4. Zander R. et al., Secular trend and seasonal variability of the column abundance of N20 above the Jungfraujoch station determined from IR solar spectra, J. Geophys. Res., 99,16745-16756,1994.

The current budget of