Low windspeeds in Irish stations

Thanks to Clive Wilson (Met Office) for informing us that the wind speeds in the Irish stations between July 1996 and August 1998 are lower than the surrounding years.  An example is shown in Fig 1. for Dublin.

Fig. 1 - Wind speeds for Dublin (039650-99999).  The vertical lines are change points detected on a monthly basis using the PHA algorithm of Menne & Williams (2009).  There is a change in resolution in the middle of 1998 coinciding with the change point.

Of the 14 Irish stations in HadISD, 12 have continuous data across this period (039520-99999 Roches Point and 039700-99999 Claremorris have no or sporadic data only across this period).  Most of the periods are identified using the PHA homogenisation algorithm that we are in the process of applying to HadISD.  

The affected stations are:

039530 99999 VALENTIA OBSERVATORY
039550 99999 CORK AIRPORT
039570 99999 ROSSLARE
039600 99999 KILKENNY
039620 99999 SHANNON AIRPORT
039650 99999 BIRR
039670 99999 CASEMENT AERODROME
039690 99999 DUBLIN AIRPORT
039710 99999 MULLINGAR
039740 99999 CLONES
039760 99999 BELMULLET
039800 99999 MALIN HEAD 

For the moment we advise users of HadISD to be cautious when using wind speed data for these stations over this period.  We are investigating the cause of this low period with the maintainers of the ISD at NCDC and will update this post when we have more information.