Climatic Research Unit: Data

Lamb Weather Types (LWTs) - Falklands

LWTs description

Reanalysis based LWTs - Falklands

Gale index from reanalysis based LWTs - Falklands



Lamb

Professor H.H. Lamb subjectively classified each day's weather over the British Isles from 1861 to February 1997. All the years have been published, except for 1996/7, in Lamb (1972) and Hulme and Barrow (1997).

Lamb Types - Number coding
-1  U           -9  non-existent day
0 A 20 C
1 ANE 11 NE 21 CNE
2 AE 12 E 22 CE
3 ASE 13 SE 23 CSE
4 AS 14 S 24 CS
5 ASW 15 SW 25 CSW
6 AW 16 W 26 CW
7 ANW 17 NW 27 CNW
8 AN 18 N 28 CN


References

Jenkinson

An objective scheme to classify the daily circulation according to the Lamb weather typing scheme was developed by Jenkinson and Collison (1977). The objective scheme uses daily grid-point mean sea level pressure data (see map below). The objective and the original subjective Lamb scheme have been compared by Jones et al., (1993). A new series has now been producuced using reanalyses data (Jones, et al., 2013). For the period from 1871-1947 the 20CR developed by Compo et al. (2011) is used and for 1948 to present the National Centers for Environmental Prediction, NCEP Reanalysis by Kalnay et al., (1996) is used. In developing a new and more consistent series, we have chosen to base the analysis data on the synoptic hour 12, as this is in the centre of the civil day to which the LWTs refer.
In order to apply the scheme to Southern Hemisphere locations the equations relating to latitude were modified, a manuscript detailing this is in preparation.
The series from 1871 to the present day (updated daily - NCEP has an approximately 6-day lag) is given here.

File format
Description of columns
day month year PM-1000 W S F Z G Dir LWT
Definitions:
PM_1000 average pressure over the grid points
W westerly flow
S southerly flow
F resultant flow
Z total shear vorticity
G gale day
Dir direction of flow
LWT see above table

Grid centred on the Falklands

Graph
Location of the grid points over the Falklands.

Filename Description
20CR_1871-1947_ncep_1948-2019_18hrs_Falklands.dat 1871-1947 20CR; 1948-present NCEP
20CR_1871-1947_ncep_1948-2019_18hrs_Falklands.csv as above in csv format (contains headers)
20CR_1948-2012_18hrs_Falklands.dat 1948-2010 (20CR to facilitate comparison)
ERA5_1979-2018_18hrs_Falklands.dat 1979-2018 ERA5

The following files provide the output described at the other synoptic hours, but they do not contain the LWT:

Filename Description
ncep_1948_2018_00hrs_Falklands.dat 1948-present NCEP 00hrs
ncep_1948_2018_06hrs_Falklands.dat 1948-present NCEP 06hrs
ncep_1948_2018_12hrs_Falklands.dat 1948-present NCEP 18hrs

Filename Description
20CR_1871-2012_00hrs_Falklands.dat 1871-2012 20CR 00hrs
20CR_1871-2012_06hrs_Falklands.dat 1871-2012 20CR 06hrs
20CR_1871-2012_12hrs_Falklands.dat 1871-2012 20CR 18hrs

Falklands Jenkinson Gale Index

The gale index G found in the above files is calculated from the following formula:

                G = [F2 + (0.5Z)2]1/2

where F is the resultant flow and Z is the total shear vorticity, see Jones et al (1993) for further details. In a similar vein to Hulme and Jones (1991) exceedances of a threshold have been counted and allocated a gale intensity:

G > 15 gale

G > 20 severe gale

G > 25 very severe gale

These thresholds were reduced by a factor of two compared to the UK, due to the grid being half the size.

This was done annually and for an extended winter (MJJASO) and summer (NDJFMA)


Filename Description
gale_index_1800hrs_Falklands.csv dated log of all G>15 events
ANN_G_thresh_counts_Falklands.pdf Annual plots of the three thresholds
MJJASO_G_thresh_counts_Falklands.pdf
Extended winter plots of the three thresholds
NDJFMA_G_thresh_counts_Falklands.pdf Extended summer plots of the three thresholds

References

Compo, G.P., Whitaker, J.S., Sardeshmukh, P.D., Matsui, N., Allan, R.J., Yin, X., Gleason, Jr B.E., Vose, R.S., Rutledge, G., Bessemoulin, P., Brönnimann, S., Brunet, M., Crouthamel, R.I., Grant, A.N., Groisman, P.Y., Jones, P.D., Kruk, M.C., Kruger, A.C., Marshall, G.J., Maugeri, M., Mok, H.Y., Nordli, Ø., Ross, T.F., Trigo, R.M., Wang, X.L., Woodruff, S.D., Worley, S.J., 2011: The Twentieth Century Reanalysis Project. Q. J. R. Meteorol. Soc. 137 1-28. DOI:10.1002/qj.776.

          Jones, P.D., Harpham, C. and Lister, D., 2015: Long-term trends in gale days and storminess for the Falkland Islands. Int. J. Climatol. 36, 1413-1427 (2016),  DOI: 10.1002/joc.4434



Last updated: March 2019, Colin Harpham

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