Diurnal Variations of 3D-Wind Cloud Height and Winds From Hurricanes and PBL
Fast atmospheric processes such as deep convection and severe storms are challenging to observe and understand without adequate spatiotemporal sampling. GEO imaging has the advantage of tracking these fast processes continuously at 10-min cadence from thermal infrared (TIR) channels. More importantly, the newly-available GEO-GEO stereo observations from our 3D-Wind algorithm allow to study the atmospheric motion vectors (AMVs) with more accurate height assignment. The stereo height, which is geometrically rather radiometrically derived, is insensitive to radiometric TIR calibration of satellite sensors. Thus, stereo height and winds are not contaminated by complex radiative transfer effects (e.g., multi-layer clouds and atmospheric inversion).
In this paper, we will present a study on the evolution of Tropical Storm Imelda (2019) and Hurricane Hanna (2020) using the stereo height and winds retrieved from the 3D-Wind algorithm. The regions where the stereo-wind high-cloud fraction and divergence retrievals for Imelda and Hanna are mapped during the period of time shortly before landfall. A strong diurnal variation in the area-averaged high-cloud fraction, divergence, and precipitation is found during the cyclone’s intensified period. The diurnal cycle of the stereo-wind divergence appears to lag the precipitation cycle by ~6 hours, followed by the high-cloud fraction. While the divergence and high-cloud fraction rise nearly simultaneously at the beginning of a diurnal cycle, the peak of cloud fraction is significantly lagging behind the divergence peak, which is expected as the increase in high-cloud fraction is initiated by the divergence in a convective system.
The 3D-Wind algorithm has also been applied to the Tonga volcanic plumes (Jan 15, 2022) and the IWWG/ICWG Golden Day (Oct 20, 2019) for inter-platform and inter-sensor comparisons. In the Tonga case we processed the three consecutive days on Jan 14-16, to track the regional diurnal variation before and after the eruption. In the Golden Day case we processed a total of five days centered on 2019D293, for the fully overlapped region from GEO-GEO and GEO-LEO (i.e., MODIS) pairings. In addition to the intercomparison study, this data set also contains rich information on diurnal variations of cloud height and dynamics in planetary boundary layer (PBL), which is another challenging region to observe with remote sensing from space. This paper will discuss the diurnal variations of PBL cloud height and winds over the Northeastern and Southeastern Pacific as observed by the stereo method and their impacts on reflected shortwave (SW) and outgoing longwave (LW) radiation. Moreover, diurnal PBL variations are found to have a significant impact on California wildfire development and plume transport. For example, the amplitude of plume heights and winds from the Creek Fire development appears to lag the fire radiative power (FRP) peak hour by ~3 hours.
