Salomon Eliasson (SMHI)Date:
AniaraAdaptation of the Nowcasting Satellite Application Facility
(NWC-SAF) Polar Platform System (PPS) cloud detection software for Inner
Arctic nighttime conditions
Determining the climate and climate change of the Arctic is of importance as many foresee that early signs of climate change may be found in the Arctic. Clouds play a very important roll on the climate and therefore it is very important to derive correct cloud climatology's if possible. The Climate Monitoring Satellite Applications Facility (CM-SAF) plans to create cloud climatology's based on Advanced Very high Resolution Radiometer (AVHRR) data derived from Polar satellites. CM-SAF uses a cloud mask from the Nowcasting Satellite Application Facility (NWC-SAF) Polar Platform System (PPS) cloud detection software for cloud detection. The PPS cloud mask was developed for European conditions at high latitudes; however the cloud mask is currently not well suited for the extreme conditions of the polar night.
An adapted PPS scheme for Arctic nighttime sea conditions is currently being implemented for the Climate Monitoring SAF project (CM-SAF). Using only infrared AVHRR satellite channels and Numerical Weather Prediction (NWP) model derived surface temperatures this scheme includes standard cloud tests currently used in many of the established cloud detection schemes, but also contains some new features which utilise the high surface temperature variance and the strong temperature inversion conditions found over the Arctic regions. The improvement lies largely in the ability to correctly distinguish warm semi-transparent clouds from cracks in the pack ice.
The adapted PPS scheme was tested on approximately 500 training targets and around 40 entire NOAA- 16 and NOAA-16 AVHRR scenes in the vicinity of the Atmospheric Radiation Measurement (ARM) site at Barrow, Alaska during the 2001/2002 winter. Preliminary results look promising. However, problems such as sensitivity to model surface temperatures and the difficulty to detect of multi-layered clouds and clouds of near-surface temperatures remain. Further evaluation of the new test sequence is planned for different years and other regions of the Arctic prior to its final implementation into the PPS software.
Created 2007-03-22 09:02:16 by Mats HolmströmLast changed 2007-03-22 09:02:16 by Mats Holmström