Abstract
Abstract. We aim to extract a universal law that governs the gravity wave manifestation in polar mesospheric clouds (PMCs). Gravity wave morphology and the clarity level of display vary throughout the wave population manifested by the PMC albedo data. Higher clarity refers to more distinct exhibition of the features, which often correspond to larger variances and a better-organized nature. A gravity wave tracking algorithm based on the continuous Morlet wavelet transform is applied to the PMC albedo data at 83 km altitude taken by the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) instrument to obtain a large ensemble of the gravity wave detections. The horizontal wavelengths in the range of ∼ 20–60 km are the focus of the study. It shows that the albedo (wave) power statistically increases as the background gets brighter. We resample the wave detections to conform to a normal distribution to examine the wave morphology and display clarity beyond the cloud brightness impact. Sample cases are selected at the two tails and the peak of the normal distribution to represent the full set of wave detections. For these cases the albedo power spectra follow exponential decay toward smaller scales. The high-albedo-power category has the most rapid decay (i.e., exponent = −3.2) and corresponds to the most distinct wave display. The wave display becomes increasingly blurrier for the medium- and low-power categories, which hold the monotonically decreasing spectral exponents of −2.9 and −2.5, respectively. The majority of waves are straight waves whose clarity levels can collapse between the different brightness levels, but in the brighter background the wave signatures seem to exhibit mildly turbulent-like behavior.
Highlights
Atmospheric gravity waves play important roles in atmospheric circulation, structure, and variability
It is worth mentioning that the case of the most distinct concentric waves shown in Fig. 2b has a combination of freq25 = 0.016 and albedo power = 25.4×10−12 sr−2, suggesting that the combination of relatively low background brightness and relatively high albedo power seem to correspond to the best clarity of wave display
A large ensemble of gravity waves reside in the polar mesospheric clouds (PMCs), and we aim to extract a universal law that governs the wave display throughout the full set of wave population
Summary
Atmospheric gravity waves play important roles in atmospheric circulation, structure, and variability. The Cloud Imaging and Particle Size (CIPS) instrument (McClintock et al, 2009) aboard the AIM satellite provides PMC images that cover the polar region daily throughout the summer season in both hemispheres, and it has collected almost 10 years of data to date These data have enabled extensive studies of gravity wave signatures in PMCs and of mesospheric dynamics more generally (e.g., Thurairajah et al, 2013; Yue et al, 2014). It is worth mentioning that in the current study we did not adopt high-pass filtering to extract the small-scale structures (e.g., Chandran et al, 2010) because 2-dimensional (2-D) filtering is prone to inducing notable artificial features if large and small scales are not separated optimally Another important technique to detect gravity waves and to resolve their characteristics is applying a spatiotemporal analysis to either the ground-based or satellite measurements (e.g., Wachter et al, 2015; Ern et al, 2011).
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