Presentation given at Solarnet 4 meeting at Lanzarote, Spain, during Jan 2017. The presentation is about Chromospheric Vector Fields derived using Ca II 854 nm spectral line observations from SOLIS/VSM instrument at NSO.

We study the temperature structure of chromospheric network fibrils using high- resolution observations from DKIST telescope. These first public release observations provide simultaneous photospheric and chromospheric spectra at high angular resolution. We use LTE and NLTE diagnostics to infer the temperature stratification in the fibrils and compare it with numerical simulations such as BIFROST.

We infer the temperature stratification in the lower solar chromosphere using the Ca II spectral line observations by the SOLIS/VSM instrument. The spectral line profiles across the full solar disk were first grouped using k-means clustering algorithm into a set of representative profiles, these profiles were then inverted under NLTE assumptions to generate a database of model atmospheres. Using a database of these representative profiles and their model atmospheres allows us to infer the temperature stratification as a function of optical depth in the lower chromosphere, for the entire set of full disk observations spanning 2010-2017, within a reasonable amount of time: given that NLTE inversions are compute intensive and time consuming. Applying our fast inversion approach to the SOLIS/VSM synoptic observations from 2010-2017 we search for long term variations in the thermal stratification of the lower solar atmosphere.