The current budget of NOy above the Jungfraujoch as derived from IR solar observations

(1)

The

current

budget of

NO,

above the

Jungfraujoch

as

derived

from

[R

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 Aeronomy, Brussels

INTRODUCTION

This paper reports on an investigation

of

a series

of

compounds

of

the NOr

family,

based on

high

ieiolution

infrared solar observations made at the ISSJ (International Scientific Station

ofthe

Jungfraujoch), Switzerland (46.55'N, 7.99oF,,3580

m a.s.l.).

These observations are part of a long+erm monitoring effort undertaken by the Liège group since the mid-1970s, 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 pm) spectrometers [1].

The columns are retrieved from the spectra by non-linear least squares spectral

fitting,

using the SFIT 1.09c algorithm; a discussion of the retrieval procedure can be found

in

_[2].

NOy BUDGET

NOr, the total reactive nitrogen, is defined as the sum of the

following

species: NO + NOz +

N0:

i

Z(NrOr) + HNOg + HOzNOz + CIONOz + BrONOz. For the purpose of deriving the

NO,

column trend above the Jungfraujoch, monthly mean columns

of

those species that can easiiy be measured from the ground, i.e. NO, NOz,

HNO:

and ClONOz, 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

high-density 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

o

deviations.

The sum of these monthly mean columns, displayed in Figure L, frame E, represents the most

important part

of

the

total NO,

as derived

from

the ISSJ

data.

The missing NO3, N2O5,

gôrNO,

und

grONOr,

not easiiy observable from the ground, represent less than

5

%

of

the total

NO,

_[3]

As for tûà

inOlviOual species,

the NO,

trend has been simulated

with a

linear+sinusoidal

funcrion (conrinuous cnrve); the resulting trend

of

(0.3

t

0.3) Vo per

_!èar,

although barely

significani, is consistent

*ith

tir"

trend

of

(0.35

t

0.04) Vo per year' found

for

the

NOt

gas

so-ur." NrO

_[4]

(Figure 2,frame

F).

The important uncertainty in the NO, trend is mainly due

to the high

"uiiàUiiity

of

the HNOE columns, which is

predominant during the November to

April

months (circulation and heterogeneous processes).

Nàtice that the constituents considered

in

the present investigation show seasonal variations summarized in the following table:

NO Noz HNOr CIONO,

Peak-to-peak v ariation (Vo\ 34 74 28 -tl

Occurrence of maximum June-July June-Julv Feb.-March March

Occurrence of minimum Januarv January August September

(2)

(+0.2 + 0.2) o/olyr (+0.7,+ 0.3\yo/yÎ C 5 4 J 2 1 22 20 '18 't6 14 12l

trl

3t

2L

1l

19€

z

Q (-0.1 + 0.4) oÂlyr {+0.3 + 0.3) oÂtyr 1 984 1 986 1 988 1 990 1 992 1 994 ' .t lt .

_.

(+0.35 + 0.04) Vo/yr

1984

1986

1988

1990

1gg2

1994

1996

Figure l: column _{abundances above ISSJ, expressed}_in_10rs_molec/cm2

o

z

JZ 30 28 zo 24 22 20 ,o 4200

o

4000

j

3800 3600

(+3.8+0.E)%/yr.

_:

_,

;..-:

:-V

rqilrprrrçir

r=,

r'.rt*rg;È4-i-Tf+trtfi

428

(3)

HNOS

AND

HF COLUMNS CORRELATION'

In

Figure 2, we have correlated the

HNO:

columns

with

those

of

HF

(with

the HF trend removed-and reported

to

1990.0) obtained on sam€ 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, generaliy correspond to air masses originating from the higher latitudes, en-riched in both HF and HNO:, u, u

ùnr"quence

of the latters' læitudinal distribution.

è

2.0 O t.8 '.a t.o G lr'

€

r.2

E

r.o

.9

0.8 o

ÉÊ

0.6

Linear fit (HF = 0.48 + 0.30 HNO3) (É=0.39)

r9B5^1989ttgg3

1986ot99o'1994

t987tl99lo1995

1e88 tssz :

_l:rll a

oo

ffi

ô'qoE

."

"È"

6 ôlL-E^ q gq o

HNO, vertical column abundance (in 1016 molec/cm2) Figure 2: HNO: and HF columns correlation

An

interesting episode

in

March

-

April

1996 is identified

in

Fig.2

by

arrows and dates; during that perioà, extremely high values

ofHF

(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

ur.r"

the edge of the vortex (on the 31't March, potential

vorticity

was 40x10-6 Km2kg-ls-l

atthe

475

K

level).

Air

masses above the Jungfraujoch originated

from

the polar resions and were thus enriched

in HF;

Figure

3

shows an example

of

back

trajectorie; for the-29th March 1996, ending at the closest rawinsonde station (Payeme, 85 km North-West

of

the Jungfraujoch). The vortex then slowly dissolved: by

mid-April,

only two

fragments remained,

oie

cetrtered over East-Siberia, the other over Central Europe. Potential

vorticity

reached

ugui"'iigï-rut*r

1:S*tOn Km2kg'rs-l

atthe

475

K

level on the 18th

April)

above the Jungfraujoch.

During that

tile

period, no specially high values

of HNO:

were observed, as we could have expecled from thé usual relati,onship between HF and HNOr shown

in

Figure 2: based on the latter, we shouldhave measure HNO3 values around 5x1016 molec./cm2instead of the values uround 1.5x1016 molec./cm2 actually observed. This suggests that denitrification occurred

in

these air parcels.

1.8 1.6 1.4 1.2 1.0 429

(4)

EC

MWF

Trajectories

1 0 d:yr rnr lyse s Floiled at N tLu b y tràh lo ô Êtd loc:p!]r rra E td U:lr: 29,IA r.1996 Lrual r a8! k O Ero roc:piy.rrr € td d.ta: 29.Ia r,1996 La!et : {15 k a Etd toc:Pat. rtt Etd dtta:29_u!r,1996 L.rat :550 k o erd lociPàt. t.

Etd dàti i9_{à1.1996 lt!at :5?5 N

Figure 3: back trajectories ending at payeme, on the 29rh 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 analvsis.

REFERENCES

1' Delbouille L' and G. Roland, High-resolution _{solar and atmospheric spectroscopy}_from_the_Jungfraujoch high-altitude station, Optical Eng., 34, 2736-2739, Igg5.

2' Rinsland C.P. et _{al.' CloNO2 total vertical column}_abundances_{above the Jungfraujoch}_Station,_19g6-7994: I-ong-term trend and winter-spring _{enhancements, J. Geophys. Res.,}_{101,3g91-3g99,}_1996.

3' Wetzel G. et _{al., Nitrogen partitioning inside}_the₁₉₉₇_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

N2O above the

Jungfraujoch station determined from IR solar spectra, J. Geophys. Res., _{99, r6745-r67s6, rgg4.}