Estimates of low-level Arctic mixed-phase cloud boundaries using multidirectional oxygen A-band retrievals
Abstract
Accurate estimation of cloud top and base heights is crucial for both energy balance measurements and aircraft operations in the Arctic. However, use of operationally relevant, passive, wide-field-of-view sensors is problematic due to the low contrast between low-level clouds and the underlying surface in visible and infrared (IR) channels. Multidirectional measurements in the near IR oxygen A-band of ~764 nm are useful for accurate retrievals of cloud-top height, and retrievals of cloud geometric thickness are possible from the angular standard deviation (Ferlay et al., 2010), but these techniques have not been attempted for high latitudes. Here we show results from a Monte Carlo radiative transfer simulation of the average photon penetration depth for various sensor view angles, seasons (i.e., solar zenith angles), optical thicknesses, and cloud geometric thicknesses, which tests the efficacy of the technique for single-layer, low-level Arctic mixed-phase stratiform clouds. We then analyze comparisons of ground-based measurements of cloud boundaries to those from a combined POLDER-MODIS product to test the accuracy of the cloud top height and thickness retrievals, as well as to quantify the relationship between cloud geometric thickness and precipitation rate (Kostinski, 2008) by including in situ precipitation rate measurements. While mixed-phase Arctic clouds can be quite complex given the intricate interactions between dynamical, microphysical, and radiative processes, their relatively simple macrophysical structure lends itself to potential exploitation for improved remote sensing and modeling of these clouds. References Ferlay, N., Thieuleux, F., Cornet, C., Davis, A. B., Dubuisson, P., Ducos, F., ... & Vanbauce, C. (2010). Toward new inferences about cloud structures from multidirectional measurements in the oxygen A band: middle-of-cloud pressure and cloud geometrical thickness from POLDER-3/PARASOL. Journal of Applied Meteorology and Climatology, 49(12), 2492-2507. https://doi.org/10.1175/2010JAMC2550.1 Kostinski, A. B. (2008). Drizzle rates versus cloud depths for marine stratocumuli. Environmental Research Letters, 3(4), 045019. http://dx.doi.org/10.1088/1748-9326/3/4/045019
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.A12B..10F