HYGROSONDE II
Esrange, Sweden, December 2001
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HYGROSONDE IIEsrange, Sweden, December 2001 |
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MISU's Atmospheric
Physics group coordinated the Hygrosonde II campaign
at Esrange,
Sweden, in December 2001. Hygrosonde II focused on the
distribution of water vapor in the middle atmosphere and
related transport processes. With these objectives, the
campaign has served as a validation and an important complement to
the Odin
satellite. Payload preparations and launch operations were
handled by Swedish Space
Corporation.
A major objective of Hygrosonde II was to provide a complete
snapshot of the water vapor distribution and related atmospheric
parameters throughout the atmosphere from the tropopause
to the mesospause. Backbone of the campaign was an improved
Hygrosonde payload for optical in situ measurements of water
vapor in the mesosphere and stratosphere. A detailed water vapor
profile in the lower and middle stratosphere was provided by
a second MISU hygrometer carried onboard a SKERRIES balloon by
the Swedish Institute for
Space Physics (IRF).
Additional experiments provided information about the vertical structure, composition and dynamics of the atmosphere: Three meteorological rockets (Falling Spheres) provided by NASA measured temperature, density and wind in the upper stratosphere and mesosphere. The SKERRIES balloon, in addition to water vapor, measured ozone, temperature, density, and wind in the lower stratosphere. The Rayleigh lidar of Bonn University provided long-term measurements of middle atmospheric temperature during periods of clear-sky conditions. Esrange's ground-based equipment (photometers, magnetometers) monitored geomagnetic and airglow conditions.
The Hygrosonde II payload was successfully launched in the early morning of December 16, 2001, at 5:12 UT. This was within an hour of the passage of the Odin satellite above Esrange. Also the three meteorological rockets and the SKERRIES balloon were launched in a well-defined launch sequence ranging from 3:11 UT until 6:18 UT.
MISU's technique for measuring water vapor both on rockets and
balloons is based on optical hygrometry.
This technique uses the dissociation of water molecules by
Lyman-alpha light, which produces hydroxyl radicals in an excited
state. Subsequent optical emission by these radicals at
wavelengths around 310 nm is detected as a direct measure of the
atmospheric water abundance. The aerodynamic design and the
pre-flight treatment of the rocket experiment ensure measurement
conditions that are not contaminated by water originating from
the payload. At stratospheric altitudes, quenching
processes become significant and alter the fluorescence spectrum
emitted by the hydroxyl. Comprehensive laboratory and model
studies have been performed to quantify these processes.
Since the first Hygrosonde
launch in 1994, the optical hygrometer technique has been
improved further. A major step has been the development a
multi-capillary Lyman-α light source, which significantly boosts
the sensitivity and signal/noise ratio of the measurement.
As an additional rocket experiment, the Hygrosonde payload carried five particle detectors provided by the University of Colorado, Laboratory for Atmospheric and Space Physics (LASP). These detectors probed the existence and distribution of heavy charge carriers in the mesosphere. Of particular interest is the connection between charged particle distribution and the dynamical structure of the atmosphere.
After recovery of the payloads and post-flight operations at Esrange, the measurement data have now been distributed to the individual scientific groups. First results will be available in early 2002.
Direct validations of Odin measurements will be possible in terms of water vapor, total density and temperature. In addition, by coordinating satellite and in situ measurements, we will obtain a unique combination of large-scale information and well-resolved local data. Hygrosonde II thus provides an important case study, measuring the local and large-scale water distribution, while simultaneously determining the dynamical input that ties both data sets together.
The dynamical information accessible by resolved local water measurement has been demonstrated earlier by the first Hygrosonde flight in 1994: The circulation of the high-latitude middle atmosphere is dominated by near-vortex dynamics and one of the important questions in this context is the response of the upper atmosphere to dynamic perturbations in the lower-lying regions. The 1994 Hygrosonde flight measured the vertical profile of water vapor in close vicinity of the edge of the polar vortex. The water mixing ratio profile showed strong stratification, coherent in upleg and downleg data. This demonstrated that air masses with different water content were transported in and out from the polar vortex. Apparently the transport of quasi-conservative trace species by horizontal motion were modulated on vertical scales of typically 5 km. The study of such structures jointly by Odin and the in situ measurements is a major aim of Hygrosonde II.
| Here are some pictures from the campaign . . . |  |
For more information about the Hygrosonde II campaign contact Misha Khaplanov (misha@misu.su.se) or Jacek Stegman (jacek@misu.su.se).
Some related publications:
The Atmospheric Physics Group
The Department of Meteorology at Stockholm University