Presentation on theme: "CARIBBEAN METOCEAN CLIMATE STATISTICS (CARIMOS)"— Presentation transcript:
1 CARIBBEAN METOCEAN CLIMATE STATISTICS (CARIMOS) Specification of the extreme and normal wind and wave climate and basin scale storm surge and 2-D currents by a hindcast approachVincent J. Cardone, PresidentOceanweather Inc.Cos Cob, CT, USA
2 CARIMOS Hindcast Approach Hindcast 109 tropical cyclones 1921 – 1999Hindcast 15-continuous years 1981 – 1995Winds and waves: triple nested approach to account for North Atlantic swell input, complex basin morphology, shallow water and island sheltering: 1.25°/.25°/.065°Basin storm surge with 2D hydro model: .25°
3 NOAA National Hurricane Center HURDAT Tape. Tropical Cyclone Deck Tropical CyclonesNOAA National Hurricane Center HURDAT Tape.Tropical Cyclone DeckAircraft Reconnaissance Data.Annual Tropical Storm Reports and Summaries.Published Accounts of Caribbean Storms.Continuous Wind FieldsNorthern Hemisphere Surface Analysis Final Analysis SeriesNOAA Tropical Strip surface analysesNOAA NCDC TDF-11 format ship report filesClimatological summariesGridded pressure fields (NCDC Global Historical Fields CD)Global so-called WMO 1000-mb wind fieldsGridded digital products of the new NOAA NCEP Global Reanalysis Project, specifically the 6-hourly 1000 mb and 10m surface wind fields.
10 Tropical Wind Model (TC96) Diagnostic PE PBL ModelWind field “snapshots”Buoy/Rig comparisons show accuracy of +/- 20º in wind direction and +/- 2 m/s in wind speedApplied in worldwide tropical basins
11 Tropical Model Snapshot Inputs Speed and direction of vortex motionEquivalent geostrophic flow of the ambient PBL pressure field in which the vortex propagatesCentral PressureScale radius of exponential radial pressure profileHolland’s profile peakedness parameter
19 Tropical Cyclone Snap Database InputOutputDp: 2 to 120 mb every 2 mbRp 5 to 120 Nmi every 4 NmiB 1 to 2.5 every .1Maximum Surface WindRadius of Maximum WindAzimuthally Averaged Wind Speed in 5 Nmi BinsRadius of 35/50 Knots
38 ValidationTropical Cyclones – rely on extensive prior validation in tropical regimes such as Gulf of Mexico, South China Sea…Continuous – utilize buoy and satellite altimeter measured winds and sea states
47 CARIMOS Derivative Products Continuous Hindcast - site specificTime series 15 years, 3-hourlyBivariate distributions (HS-TP, HS-VMD, WS-WD) Duration/persistence distributionsExtremesTime series in storms, hourlyReturn period extremes of WS, HS, HM, HC, TP, Va, Sh 1 year to 100 years
48 CARIMOS Wind and Wave Fields Definitions DescriptionDateJulian format (where Jan = 1, Jan = 2, etc.)Wind DirectionFrom which the wind is blowing, clockwise from true north in degrees (meteorological convention).Wind Speed1-hour average of the effective neutral wind at a height of 10 meters, units in meters/second.
49 Total Spectrum Wave Fields: Total VarianceThe sum of the variance components of the hindcast spectrum, over the 552 bins of the wave model, in meters squared.Significant Wave Height4.000 times the square root of the total variance, in meters.Peak Spectral PeriodPeak period is the reciprocal of peak frequency, in seconds. Peak frequency is computed by taking the spectral density in each frequency bin, and fitting a parabola to the highest density and one neighbor on each side. If highest density is in the Hz bin, the peak period reported is the peak period of a Pierson-Moskowitz spectrum having the same total variance as the hindcast spectrum.Vector Mean DirectionTo which waves are traveling, clockwise from north in degrees (oceanographic convention).
50 Second Spectral Moment First Spectral MomentFollowing Haring and Heideman (OTC 3280, 1978) the first and second moments contain powers of = 2f; thus:where dS is a variance component and the double sum extend over 552 bins.Second Spectral Momentwhere dS is a variance component and the double sum extend over 552 bins.Dominant DirectionFollowing Haring and Heideman, the dominant direction is the solution of the equationsThe angle is determined only to within 180 degrees. Haring and Heideman choose from the pair (, +180) the value closer to the peak direction.
51 In-Line Variance Ratio Angular SpreadingThe angular spreading function (Gumbel, Greenwood & Durand) is the mean value, over the 552 bins, of cos( -VMD), weighted by the variance component in each bin. If the angular spectrum is uniformly distributed over 360 degrees, this statistic is zero; if uniformly distributed over 180 degrees, 2/; if all variance is concentrated at the VMD, 1. For the use of this statistic in fitting an exponential distribution to the angular spectrum, see Pearson & Hartley, Biometrika Tables for statisticians, 2:123 ff.Angular spreading (ANGSPR) is related to cosn spreading as follows:n = (2*ANGSPR)/(1-ANGSPR)In-Line Variance RatioDirectional spreading by Haring and Heideman, p Computed as:If spectral variance is uniformly distributed over the entire compass, or over a semicircle, Rat = 0.5; if variance is confined to one angular band, or to two band 180 degrees apart, Rat = According to Haring and Heideman, cos^2 spreading corresponds to Rat = 0.75.
52 Wave Partition Fields (Sea/Swell): Total Variance of “Sea” PartitionPeak Spectral Period of “Sea” PartitionVector Mean Direction of “Sea” PartitionTotal Variance of “Swell” PartitionPeak Spectral Period of “Swell” PartitionVector Mean Direction of “Swell” PartitionExplanation of sea/swell computation:The sum of the variance components of the hindcast spectrum, over the 552 bins of the wave model, in meters squared. To partition sea (primary) and swell (secondary) we compute a P-M (Pierson-Moskowitz) spectrum, with a cos3 spreading, from the adopted wind speed and direction. For each of the 552 bins, the lesser of the hindcast variance component and P-M variance component is thrown into the sea partition; the excess, if any, of hindcast over P-M is thrown into the swell partition.
53 Sample Storm Peak Table Storm Peaks23 Peaks found > 4 within a window of 72 hours.CS Gpt 3106, Lat 15.0n, Long 75.0w, Depth mDefined Period: StormsDate Ranges: 9/8/ :00 to 10/2/ :00CCYYMM DDHHmm WD WS ETOT TP VMD MO1 MO2 HS DMDIR ANGSPR INLINE HSUR CS CD MaxWAVE CREST W/HS C/HSdeg m/s m^2 sec deg m^2/s m2/s m deg cm cm/s deg m m
54 Computation of Maximum Individual Wave Height in a Storm The program evaluates Borgman's (1973) integral:where H is the largest wave height; a2 is the mean square height taken as a function of time, t; ta and tb are the beginning and end of the storm; and T(t) is the wave period, taken here is the significant wave period.Maximum Individual Wave Height (Forristall, 1978):T = M0/M1
55 Computation of Maximum Individual Crest Height in a Storm Maximum Crest Height (Haring and Heideman, 1978):where h is elevation and d is water depthT = .74 TP TP is the reciprocal of fpeak, found by solvingby inverse interpolationThe median of the resulting distribution was taken as the maximum expected single peak in the storm.
56 Extremal Analysis Storm Peak Table Issues Peaks over threshold vs annual maximumSelection of distributionSelection of fitting thresholdSite averaging
57 Algorithm - Return-Period Extremes Calculation of Return-Period Extremes The distributional assumptions used are:Gumbel distribution of extremes:Borgman distributions of extremes, i.e., Gumbel distribution of squared extremes:3. Galton distribution of height, i.e. normal distribution of log heights:4. Weibull distribution described in next sectionThe fitting procedure of Gumbel (1958, pp ) was followed for Gumbel, Borgmanand Galton, with plotting positions based in i/(n+1), often called Weibull plotting position., where
60 Significant Wave Height Interannual Variability of Exceedence Value
61 Significant Wave Height Interannual Variability of Exceedence Value
62 ConclusionsDemonstration that CARIMOS provides a very skillful model for normal conditionsImportance of due consideration to decadal climatic trends, 25% difference in extreme wave heightsImportance of due consideration in inter- annual variability upto 100% difference in values of 90% and 99% exceedences