logo
Skip to content

Our Activities

breadcrumb border breadcrumb border

Scholarship Reports

report

An Insight into CSIP

Carolyn Cook

The Convective Storm Initiation Project (CSIP) was established to increase the understanding of the initiation of convective storms. At present this understanding is limited, leading to poor forecasting. Consider, for example, the events in Boscastle on the 16.08.05 where immense flash flooding occurred and homes were destroyed. Fortunately in this case there were no fatalities, however, if the people of Boscastle had been given prior warning then they could have at least been prepared and protected some of their property. It is events such as this that provide motivation for CSIP.

 

Preparation for CSIP was carried out in 2004 when a pilot project ran. The results of the pilot project revealed a great deal about the instrumentation that was to be used and the information that would be obtained, Morcrette et al (2005) provide further detail. The project lasted for 3 months from 05.06.2005 to 26.08.2005 and during this time there were 18 IOPs (Intense Observation Periods). An IOP only occurred if it was thought that the weather conditions looked favourable for convective activity; this was decided by a team of experienced meteorologists and the Met office forecast model. When deciding whether an IOP would occur or not, one of the key features was the amount of Convective Available Potential Energy (CAPE) shown in the model Tephigrams. CAPE is the buoyancy of an air parcel vertically integrated between the level of free convection (LFC) and the level of neutral buoyancy (LNB) at which the parcel ceases to have virtual potential temperature of the environment and thus decelerates vertically. Therefore, if the model Tephigrams revealed high values of CAPE then an IOP would be called. It could be correctly argued that this puts a lot of faith in the model used to produce the tephigram, however, other parameters were also analysed including satellite and radar imagery.

Once the decision had been made the CSIP group sprang into action and within 2 hours of the decision being made observations could be taken throughout the CSIP area. The CSIP area is centred on the Chilbolton radar and covers a region of radius 90km from this focal point. Throughout this area 6 radiosonde sites and 16 Automatic Weather Stations (AWS) were positioned strategically so as to obtain maximum coverage. These are just two of the many instruments used to obtain measurements; overall the instrumentation used for CSIP was vast. Figure 1 shows the location of all the instruments and the more interested reader is referred to Morcrette et al (2005).

Throughout each IOP radiosondes would be launched every hour on the hour from observation sites. This was so that the ascent from each radiosonde could be compared, however there were difficulties in ensuring that all radiosondes were launched at the same time due to both instrument and human error. For example when there were high winds the event of a balloon bursting was more likely, this meant that further time was then required to inflate another balloon. These events were rare; however they should still be taken into account. Further interest evolves when considering the area that each radiosonde represents and which radiosonde site would provide the most accurate representation of a storm or shower within the CSIP area. Such interest provided motivation for my third year project entitled, “The Representativeness of Radiosondes”. All other instruments would operate continuously.

After each IOP a debrief was held where all the key features of that day were highlighted and the possible causes of convection, based on the observations, were considered. These meetings were extremely useful as they created inspiration for future analysis. The analysis that was carried out during CSIP was limited due to the time that was required ensuring that the instrumentation was fully functional and collecting the measurements.

One area that was constantly under review during an IOP was the evolution of the lids. A lid is an inversion within the atmosphere that restricts the vertical motion of an air parcel. If a lid was observed to strengthen then convective activity would be restricted whereas if a lid weakens then convective activity is enhanced. Many questions arise when considering the evolution of a lid, for example; what exactly causes the lid to weaken; how weak does a lid have to be to enhance convection; or alternatively how strong does convection have to be to break a lid and how exactly does a lid form in the first place? By studying the 18 IOPs these questions should be answered. The seemingly intuitive observation was made that as the surface is warmed and convection increases it is common to see the lids increase with height due to the convection forcing it upwards. However, an attempt at quantification of these observations should be made to make such observations more sound.

It is difficult to express the extent of the work carried out during CSIP without going into detail of each IOP. This is due to the differences in each IOP, each of which have their individual merits, some stronger than others. The analysis of the data obtained will not be complete for some time yet due to the scope of the project, however, when it is complete the understanding of the initiation of convective storms will most certainly be improved and if quantification of the results is successful then it can also be expected for forecasting to advance.