Case Study: 29 - 30 January 1998

• I. Introduction and Short Description of the Case
• Introduction
• The situation over the Arctic Sea before the development
• II. Analysis for 29 January 1998 06.00 UTC - Early Wave Stage
• 06.00 UTC - Satellite Overview
• 06.00 UTC - Frontal, Wave and Jet Streak diagnosis
• 06.00 UTC - Cross sections
• III. Analysis for 29 January 1998 12.00 UTC - Developing Wave Stage
• 12.00 UTC - Satellite Overview
• 12.00 UTC - Frontal and Wave diagnosis
• 12.00 UTC - Cross sections
• IV. Analysis for 29 January 1998 18.00 UTC - 30 January 1998 06.00 UTC - Rapid Development
• Rapid Development - Introduction
• Rapid Development - Satellite Overview
• Diagnosis of surface and Upper Level Lows
• Diagnosis of frontal parameters
• PVA and jet streak diagnosis
• Rapid Development - Cross sections
• Diagnosis of precipitation patterns with help of relative streams and NORDRAD radar
• V. Overview of Period 30 January 06.00 UTC - 18.00 UTC - Further Development of the Occlusion and ECMWF - HIRLAM Model Comparison
• Further development of the Occlusion
• Additional invesstigation: Comparison of HIRLAM fields vs. ECMWF fields of isotachs and PVA at 300 hPa

Rapid Development - Satellite Overview

As the most striking cloud structure features were still located north of 60° latitude, the geostationary satellite data is not the best tool for visualizing the development of cloud systems. For this reason a series of consecutive NOAA satellite passes are shown in the following:

29 January 1998/14.36 UTC - NOAA CH4 image	29 January 1998/16.16 UTC - NOAA CH4 image; B: cloud bulge, C: Comma, H: cloud head, J: Jet Fibre Cloudiness, W: Wave
30 January 1998/01.29 UTC - NOAA CH5 image	30 January 1998/06.02 UTC - NOAA CH4 image

The sequence of four NOAA IR channel (channel 4 or channel 5) images are shown to visualize the evolution of the wave cloud into a spiral-formed mature occluded storm. The first two images show the development a few hours after 12.00 UTC. These images show quite complex structures in the developing Wave (marked with W in 16.16 UTC image (right image top)). The cloud head (marked respectively with H) is becoming more and more pronounced. The images show also yet another cloud bulge emerging from beneath the cloud head (marked with B). The Jet Fibre Cloudiness indicating the location of the jet streak is also clearly seen (marked with J). A distinct Comma cloud pattern (marked with C) associated with the upper level trough can be seen north of the Lofoten Islands.

Unfortunately there is a several hours gap in NOAA passes during the evening and night. However, the first image for 30 January at 01.29 UTC (left image bottom) indicates that during the evening and night the system has developed considerably from a Wave into a cyclone with spiral cloudiness rotating around the vortex (centred in west Finland). The former head of the cloud is most probably seen almost as a separate hammer-like feature around 65N/22E.

The continuing development can be seen in the 06.02 UTC image (right image bottom) for the same day. This image indicates that the cloud vortex is very intensive. The cloud mass with the brightest tops has moved further south-east. The former head of the cloud is now moving southwards in a strong northerly air stream.