Climatic Research Unit : Data : LWT

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

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

Hulme, M. and Barrow, E. (Editors), 1997: Climate of the British Isles: present, past and future, Routledge, London, 454pp.

Lamb, H.H., 1972: British Isles Weather types and a register of daily sequence of circulation patterns, 1861-1971. Geophysical Memoir 116, HMSO, London, 85pp.

Lamb, H.H., 1991: British Isles daily wind and weather patterns 1588, 1781-86, 1972-91 and shorter early sequences (in 1532, 1570 and other years, notably 1688, 1689, 1694, 1697, 1703, 1717, 1783-4, 1791, 1792, 1795, 1822, 1825, 1829, 1845, 1846, 1849, 1850, 1854-5. Climate Monitor 20, 47-70.

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

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

Location of the grid points over the Falklands.

Filename	Description
20CR_1871-1947_ncep_1948-2021_18hrs_Falklands.dat	1871-1947 20CR; 1948-present NCEP
20CR_1871-1947_ncep_1948-2021_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_2021_00hrs_Falklands.dat	1948-present NCEP 00hrs
ncep_1948_2021_06hrs_Falklands.dat	1948-present NCEP 06hrs
ncep_1948_2021_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.

Hulme, M. and Jones P.D., 1991: Temperatures and windiness over the United Kingdom during the winters of 1988/89 and 1989/90 compared with previous years. Weather, 46, 126-136, DOI: 10.1002/j.1477-8696.1991.tb05724.x

Jenkinson, A.F. and Collison, F.P., 1977: An initial climatology of gales over the North Sea. Synoptic Climatology Branch Memorandum No. 62, Meteorological Office, Bracknell.

Jones, P.D., Hulme, M. and Briffa, K.R., 1993: A comparison of Lamb circulation types with an objective classification scheme. Int. J. Climatol. 13, 655-663.

Jones, P.D., Harpham, C. and Briffa, K.R., 2013: Lamb Weather Types derived from Reanalysis Products. Int. J. Climatol. 33, 1129-1139, DOI: 10.1002/joc.3498

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

Kalnay, E., Kanamitsu, M., Kistler, R., Collins, W., Deaven, D., Gandin, L., Iredell, M., Saha, S., White, G., Wollen, J., Zhu, Y., Chelliah, M., Ebisuzaki, W., Higgins.,W., Janowiak, J., Mo, K.C., Ropelewski, C., Wang, J., Leetmaa, A., Reynolds, R., Jenne, R. and Joseph, D., 1996: The NCEP/NCAR 40-year reanalysis project. Bulletin of the American Meteorological Society, 77, 437-471.

Last updated: Feb 2021, Colin Harpham

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Please use the attribution Climatic Research Unit, University of East Anglia