Abstract. High-altitude cirrus clouds are climatically important: their formationfreeze-dries air ascending to the stratosphere to its final value, and theirradiative impact is disproportionately large. However, their formation andgrowth are not fully understood, and multiple in situ aircraft campaigns haveobserved frequent and persistent apparent water vapor supersaturations of5 %–25 % in ultracold cirrus (T<205 K), even in the presence of iceparticles. A variety of explanations for these observations have been putforth, including that ultracold cirrus are dominated by metastable ice whosevapor pressure exceeds that of hexagonal ice. The 2013 IsoCloud campaign atthe Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud andaerosol chamber allowed explicit testing of cirrus formation dynamics atthese low temperatures. A series of 28 experiments allows robust estimationof the saturation vapor pressure over ice for temperatures between 189 and235 K, with a variety of ice nucleating particles. Experiments are rapidenough (∼10 min) to allow detection of any metastable ice that mayform, as the timescale for annealing to hexagonal ice is hours or longer overthe whole experimental temperature range. We show that in all experiments,saturation vapor pressures are fully consistent with expected values forhexagonal ice and inconsistent with the highest values postulated formetastable ice, with no temperature-dependent deviations from expectedsaturation vapor pressure. If metastable ice forms inmore »
This content will become publicly available on July 5, 2023
Coexistence of vitreous and crystalline phases of H 2 O at ambient temperature
Formation of vitreous ice during rapid compression of water at room temperature is important for biology and the study of biological systems. Here, we show that Raman spectra of rapidly compressed water at greater than 1 GPa at room temperature exhibits the signature of high-density amorphous ice, whereas the X-ray diffraction (XRD) pattern is dominated by crystalline ice VI. To resolve this apparent contradiction, we used molecular dynamics simulations to calculate full vibrational spectra and diffraction patterns of mixtures of vitreous ice and ice VI, including embedded interfaces between the two phases. We show quantitatively that Raman spectra, which probe the local polarizability with respect to atomic displacements, are dominated by the vitreous phase, whereas a small amount of the crystalline component is readily apparent by XRD. The results of our combined experimental and theoretical studies have implications for detecting vitreous phases of water, survival of biological systems under extreme conditions, and biological imaging. The results provide additional insight into the stable and metastable phases of H 2 O as a function of pressure and temperature, as well as of other materials undergoing pressure-induced amorphization and other metastable transitions.
- Award ID(s):
- 2104881
- Publication Date:
- NSF-PAR ID:
- 10382975
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 119
- Issue:
- 27
- ISSN:
- 0027-8424
- Sponsoring Org:
- National Science Foundation
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