Kiruna 1998
The measurement campaign at Kiruna (67.84°N, 20.41°E, 425 m MSL), Sweden, in 1998 lasted from 26 January to 03 April and spectra of the stratospheric trace gases ClO, O3 and N2O in the frequency range from 268 GHz to 279 GHz were measured. The inversion was performed with modified Tikhonov-Phillips-Regularization and Optimal Estimation Method. In the following a selection of spectra and inverted profiles is presented.
Hardware Description
The quasioptical frontend uses a Martin-Puplett interferometer to suppress noise and atmospheric signatures from the unused sideband and a Fabry-Pérot interferometer as diplexer to feed the local oscillator (LO) to the mixer. The LO operating at 276.3 GHz uses a Gunn oscillator at 92.1 GHz and a tripler. For high frequency stability a phaselock system is applied. The downconversion to the intermediate frequency of 2.1 ± 0.5 GHz is performed by a cryogenic single-ended Schottky mixer operating at about 100K. The LN2 dewar also encloses the low noise IF amplifier and two cold loads. The systems noise temperature including quasioptics and the low-noise cryogenic amplifier is 800 K at center frequency. Baseline ripples caused by standing waves in the quasioptical transmission path are suppressed by a rooftop like mirror reciprocating by about 0.4 mm. The high spectral resolution of 1 MHz over an instantaneous IF bandwith of 1 GHz is achieved by an acusto-optical spectrometer.
A schematic overview of the concept is visualized in the figure beside.
ClO-Measurements
From 28 January to 2 February continuous monitoring of ClO over Kiruna was possible due to favourable weather conditions resulting in a timeseries of ClO vmr profiles covering this whole timespan.
Time series of ClO over Kiruna lasting from 28 January to 2 February 1998. The lower ClO layer at about 20 km and its diurnal variation indicating chlorine activation can clearly be seen. This diurnal variation ist the result of the formation of the ClO dimer in the night. In the morning after sunrise this ClO dimer is photolyzed and ClO is released again. There is a weaker diurnal variation of the upper ClO layer at about 35 km due to the photolyses of chlorine nitrate which is indicated in the graph.
O3-Measurements
A complete time series of ozone vmr profiles for the whole duration of the campaign in 1998 could be retrieved. The series is composed from measurements at the strong ozone lines at 273.051 GHz and 274.478 GHz, if available. Else the results of the joint retrieval of N2O or ClO were used.
Ozone vmr profiles from 26 January to 3 April 1998. An increase of the vmr values in an altitude at about 35 km in March probably due to the breakup of the polar vortex is obvious.
Comparison of the vmr values at 27.3 km and the potential vorticity at 550 K.
On 27 March 1998 there was an ozonsonde launch at ESRANGE, Kiruna.
Upper graph: Ozone spectrum measured on 27 March.
Lower graph: The resulting vmr profile shows a good agreement with the ozonesonde data.
N2O-Measurements
At the measurement campaign 1998 N2O measurements inside and outside the polar vortex were performed. Both in the spectra and in the retrieved vmr profiles the sinking of N2O inside the polar vortex is visible.
N2O measurements outside (6 February) and inside (23 February) the polar vortex. The upper graph shows the measured spectra and the lower graph the retrieved profiles. The sinking airmasses inside the polar vortex lead to a sinking of N2O.