Response Functions of the Ultraviolet Filters ofTRACEand the Detectability of High‐Frequency Acoustic Waves

Abstract

We have used detailed non-LTE radiation hydrodynamic simulations to investigate the detectability of high-frequency acoustic waves with the Transition Region And Coronal Explorer (TRACE). A broad spectrum of acoustic waves are fed into the computational domain at the lower boundary of the model atmosphere, and TRACE UV continuum intensities are calculated by folding the derived intensities with the TRACE filter transmission functions for the 1700 and 1600 filters. Power spectra, phase diagrams, and intensity response functions are calculated, and intensity formation heights are derived. The simulations show that the average response height of the 1700 and 1600 passbands are 360 and 430 km, with widths of 325 and 185 km. The width of the TRACE intensity response functions reduces the power of the intensity oscillations considerably, but if waves are present with power enough to be of importance for the energy balance of the chromosphere, they should be detectable at least up to 40 mHz in the absence of instrumental noise, especially in the 1600 passband. The phase difference between the synthesized 1600 and 1700 TRACE intensities follows the curve expected for propagating acoustic waves up to 15 mHz. For higher frequencies the phase difference decreases and approaches zero before the coherence drops down, similar to the observed behavior. This is explained by the double-peaked nature of the response function for the 1700 intensities.