HAO 2011 Profiles In Science: Dr. Ingrid Cnossen

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Dr. Ingrid Cnossen is a Post Doc I at the High Altitude Observatory at NCAR. She is studying the effects of long-term changes in the Earth's magnetic field on magnetosphere-ionosphere interactions and on the ionosphere itself, using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model.

Publications

Simulations-strong dipole and weak dipole to strong dipole

Figure 1: High resolution

(1) The response of the coupled magnetosphere-ionosphere-thermosphere system to a 25% reduction in the dipole moment of the Earth's magnetic field

Abstract: In order to understand how changes in the dipole moment of the Earth';s magnetic field may affect the magnetosphere-ionosphere-thermosphere system, Ingrid Cnossen and colleagues performed simulations with the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model, first using a dipole moment of 81022 Am², close to the present-day value ("strong dipole"), and then a dipole moment of 6•10²² Am², which may be its value a few centuries in the future ("weak dipole"). Both simulations were run under the same solar wind conditions, for intermediate solar activity (F10.7 = 150), at equinox. Substantial differences are predicted for the ionosphere. The left column of Figure 1 shows ionospheric quantities for the "strong dipole", averaged over the two hours 13–15 UT: the height of the peak of the F2 layer, hmF2 (top); the vertical component of the neutral wind parallel to the magnetic field, v_{n, par, v} (middle), which forces the plasma up and down field lines; and the vertical component of the ExB drift (bottom). The right column shows the changes in these quantities when the dipole moment is reduced. Changes in v_{n, par, v}, explain the changes in hmF2 over the Pacific, off the south-east coast of Australia, and over east Asia. The changes in the neutral wind themselves are caused partly by an enhancement in ExB ion drift velocities (through ion-neutral collisions) and partly through an increase in the meridional pressure gradient, in response to stronger high-latitude Joule heating. Changes in the vertical component of the ExB drift, which is most effective in changing hmF2 at low latitudes, may be responsible for the decrease in hmF2 over the Indian Ocean. There is also a global mean uplift of the ionosphere, due to an increase in global mean temperature, which causes the thermosphere to expand.

(2) Climate change in the upper atmosphere

Figure 2: High resolution

Ingrid Cnossen wrote a chapter on "Climate change in the upper atmosphere" for the book Greenhouse Gases / Book 1, to be published by Intech Open Access Publishers in December 2011. In the upper atmosphere, a long-term cooling trend has been observed, along with a corresponding reduction in density at fixed height (the result of thermal contraction) and changes in the ionosphere. An increase in the concentration of CO₂, a coolant in the upper atmosphere, is responsible for some of the observed change. However, model estimates of the effects of historical changes in CO₂ concentration tend to be much smaller than the observed trends in the thermosphere. An example for the change in temperature is shown in the figure below. While changes in the middle atmosphere (30–90 km) can be largely explained, the warming trend in the lower thermosphere (an artifact of the contraction of the upper atmosphere, resulting in the downward displacement of the temperature profile) and the cooling trend in the upper thermosphere (>200 km) are both much larger than model estimates. Other factors that may influence the climate of the upper atmosphere must therefore be considered and quantified as well in order to explain observed changes. The chapter reviews our current knowledge of the effects of changes in composition (CO₂, ozone, methane, and water vapor), the secular variation of the Earth’s magnetic field, long-term changes in solar and geomagnetic activity, and changes in tides propagating upwards from the lower atmosphere.

Figure 2 caption: Observed and modelled temperature trends (dots) with error bars where available (lines). Note that modelling results are in black/grey while observational results are in colour. For Akmaev et al. (2006) both January and March results are shown (stronger trends are for January) and for Cnossen (2009) both March and June results are shown (stronger trends are for June, though there is only a small difference). All other results are seasonal averages.

References

Akmaev, R.A., Fomichev, V.I., & Zhu, X. (2006). Impact of middle-atmospheric composition changes on greenhouse cooling in the upper atmosphere. J. Atmos. Solar-Terr. Phys., Vol.68, No. 17, pp. 1879-1889.

Beig, G., Keckhut, P., Lowe, R.P., et al. (2003). Review of mesospheric temperature trends. Rev. Geophys., Vol. 41, No. 4, 1015.

Cnossen, I. (2011), Climate change in the upper atmosphere, in: Greenhouse Gases / Book 1, edited by Liu, G., InTech, ISBN 979-953-307-224-0, in press.

Cnossen (2009). Modelling of long-term trends in the middle and upper atmosphere. PhD thesis, University of Leicester, Leicester, UK.

Donaldson, J.K., Wellman, T.J., & Oliver, W.L. (2010), Long-term change in thermospheric temperature above Saint Santin, J. Geophys. Res., Vol. 115, A11305.

Semenov, A.I. (1996). Temperature regime of the lower thermosphere from emission measurements during the last decades. Geomagn. Aeron., Vol. 36, No. 5, pp. 90-97.

She, C.-Y., Krueger, D.A., Akmaev, R.A., Schmidt, H., Talaat, E., & Yee, S. (2009). Long-term variability in mesopause region temperatures over Fort Collins, Colorado (41°N, 105°W) based on lidar observations from 1990 through 2007.

Qian, L., & Solomon, S.C. (2011). Thermospheric density: an overview of temporal and spatial variations, Space Sci. Rev., in press, doi.: 10.1007/s11214-011-9810-z.

Zhang, S.-R., Holt, J.M., & Kurdzo, J. (2011), Millstone Hill ISR observations of upper atmospheric long-term changes: Height dependency, J. Geophys. Res., Vol. 116, A00H05.