Solar Cycle Variations of the Chromospheric Prolateness

The solar chromospheric prolateness or ovalisation is episodically measured using both i/ images taken in cool chromospheric lines and ii/ using a spectroscopic method to evaluate the average thickness of the extended chromosphere. We note the importance of paying attention to effect due to coronal holes which dominate in the case of the He lines and obviously, in the case of coronal lines observed in space. We discuss the solar cycle variations of the prolateness effect telling us the possible role of the emerging network magnetic fields toward the chromosphere and toward the inner corona and its interaction with the more global field to produce a seemingly lifting effect in polar regions. New methods of observations should be used, including time and spatial averaging of the chromospheric outer boundary. We finally offer some suggestions to permit a routine measurement of this lifting effect.