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Using a full spectral scan of an active region from the Extreme-UltravioletImaging Spectrometer (EIS) we have obtained Emission Measure EM$(T)$distributions in two different moss regions within the same active region. Wehave compared these with theoretical transition region EMs derived for threelimiting cases, namely \textit{static equilibrium}, \textit{strongcondensation} and \textit{strong evaporation} from \cite{ebtel}. The EMdistributions in both the moss regions are strikingly similar and show amonotonically increasing trend from $\log T[\mathrm{K}]=5.15 -6.3$. Usingphotospheric abundances we obtain a consistent EM distribution for all ions.Comparing the observed and theoretical EM distributions, we find that theobserved EM distribution is best explained by the \textit{strong condensation}case (EM$_{con}$), suggesting that a downward enthalpy flux plays an importantand possibly dominant role in powering the transition region moss emission. Thedownflows could be due to unresolved coronal plasma that is cooling anddraining after having been impulsively heated. This supports the idea that thehot loops (with temperatures of 3{-}5 MK) seen in the core of active regionsare heated by nanoflares.

Evidence of Impulsive Heating in Active Region Core Loops