数值模型演示幻灯片.ppt

Click to edit Master title style,*,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,Numerical Models,An Overview and Tutorial,1,Types of Models,Short range models,These tend to be more suitable for more specific features such as fronts,temperatures,and convection.They are considered non-hydrostatic.,Forecasting for as little as the next 1 hour to as long as 3 days.,Long range models,These are hemispheric or global models and are highly skilled at wave patterns within the jet stream.However they also have skill at synoptic features and an outperform the short range models at times!These are usually hydrostatic or isentropic.,Forecasting out to as far as 15 days,For an understanding of terms such as hydrostatic or isentropic,we encourage you to look outside this tutorial(google it!)to get an overview.,2,So many models!,RUC Rapid Update Cycle,NAM North American Mesoscale,WRF-NMM,WRF-ARW and WRF-HRW,GFS Global Forecast Systems,ECMWF European Center for Medium Range Weather Forecasting,NGM Nested Grid Model(being phased out.),3,So many models!,GEM Global Environmental Multiscale(Canada),UKMET United Kingdom Meteorological Model,NOGAPS Navy Operational Global Atmospheric Prediction System,Hurricane models such as the HWRF,GFDL,and WW3,4,Let us narrow it down,For the purposes of this tutorial we will only concentrate on the models most used here at NEXLAB.,And they are.,RUC,WRF,GFS,And to a certain extent the ECMWF and GEM,Oh,and there is ensemble forecasting,too.But well get to that later,5,Rapid Update Cycle(RUC),The RUC is a very short range model with forecasts as short as 1 hour.,Many versions of the RUC run at places such as NCEP,FSL,local weather offices,and even colleges.The operational model comes out of NCEP and is run every hour.,Every three hours(0Z,3Z,6Z,etc.)it runs a forecast out to 12 hours.During the hours in between it forecasts only for the next 3 hours.So,at 0Z you get forecast through 12Z but at 1Z you get a forecast valid through 4Z,Generally used for the 1,2,3,6,9,and 12 hour forecast period but as mentioned before,many versions and suites of the RUC are run so this is not always the case.But this is what you see on our website here at COD.,RUC Analyses often used for“analysis”data such as the SPC meso-analysis page so understanding the RUC can be vital in modern day forecasting.,6,Rapid Update Cycle(RUC),The lastest version of the RUC(as of September 2008)has a horizontal resolution of 13km and 50 layers through the depth of the atmosphere.,Much information can be found about the RUC at,maps.fsl.noaa.gov/,7,Rapid Update Cycle(RUC),This is the domain of the RUC-13km model.Data is taken a grid point spaced every 13km throughout this entire region(but only this region!),8,Rapid Update Cycle(RUC),This is the 12Z RUC,3 hour forecast of surface theta-e,valid at 15Z,.,9,North American Mesoscale(NAM),The NAM is the operational short range model run by NCEP.,The actual model itself is called the WRF(Weather Research and Forecasting),and more technically the WRF-NMM(Nonhydrostatic Mesoscale Model).,The WRF,like the RUC,is run different ways by different places.You may see references to the WRF-ARW(Advanced Research),too.,With all that being said,the NAM is the operational run and uses the WRF-NMM model for the basis of operational forecasting.If you see NAM or WRF,it simply means you are looking at the WRF-NMM model.,Confused yet?Dont worry because the models are always changing names.,I encourage you to look at the WRF homepage at,www.wrf-model.org/index.php,10,North American Mesoscale(NAM),The NAM/WRF is run four times a day at 00Z,6Z,12Z,and 18Z.,The NAM/WRF does a forecast for every 6 hours out to 84 hours from the time it is run,or 3 days.,The NAM/WRF is set up as a non-hydrostatic model run at 12km of horizontal resolution and has 60 layers through the depth of the atmosphere.,Further learning about the NAM resolution can be found at,www.meted.ucar.edu/nwp/pcu2/namhres1.htm,11,North American Mesoscale(NAM),This is the domain of the WRF-12km model.Data is taken a grid point spaced every 12km throughout this entire region(but only this region!),12,North American Mesoscale(NAM),This is the 12Z WRF,6 hour forecast of QPF(precipitation),valid at 18Z,13,Global Forecast System(GFS),The GFS is a short,medium,and long range model with forecasts out to 384 hours.,The GFS forecasts for every 6 hours(00Z,6Z,12Z,and 18Z)out to 180 hours,then every 12 hours out to 384 hours.,At 180 hours the resolution is not as fine so the user will see less detail in products beyond 180 hours.,The GFS has 64 layers throughout the depth of the atmosphere with a horizontal resolution of 30km(though 180hrs).,14,Global Forecast System(GFS),The GFS is a global model run for the northern hemisphere(the domain is shown above)and for the southern hemisphere.This is one reason the GFS is very,skilled at wave patterns and overall jet stream flow.,15,Global Forecast Systems(GFS),This is the 00Z GFS,9 day forecast of 500 speeds,valid at 00Z of day 9,16,The Products,Speeds(jets),Vertical Velocity and vorticity products,Temperature fields,Humidity and moisture,Thicknesses and precipitation(QPF),Instability and shear fields,17,The Products-Speeds,GFS(in this case),500mb speeds,Jet maxima,Heights,Upper lows,Ridge,Wind barbs,Color bar(key),L,L,Products like this can be found on just about every model for major layers of the upper atmosphere such as 250mb,500mb,700mb,and 850mb.Some models will include a few layers in between,as well,.,18,The Products Vorticity,Vorticity is a complicated thing to understand.For the basis of this tutorial we will only discuss the basics.You are encouraged to learn more about vorticity on your own!,Essentially,vorticity is the spin of the air.The more the air is sheared,or spun,the higher the value of vorticity.,Vorticity is generally displayed on a 500mb map due to the fact that 500mb is in the middle of the troposphere.,When looking at a vorticity map,the center of vorticity(the maximum value)is generally associated with the heart of a shortwave trough.It might be referred to as a“vortmax”,Areas downwind of this vorticity center(where vorticity is being advected positively)can be understood to be an area of upward vertical motion.Consequently,areas upwind of the shortwave trough where vorticity is decreasing can be understood to have sinking air.Again,this is a simplified understanding of vorticity but does have practical applications.,19,The Products-Vorticity,GFS(for this case),500mb Vorticity,500mb Heights,Vorticitiy Maximum(vortmax),Shortwave troughs,Color Bar,X,X,X,X,X,20,The Products Vertical Velocities,The Vertical Velocity product(or VVs or UVVs for upward vertical velocities)is simply a measure of how much the air is rising or sinking.,This is a measure of overall rising air(synoptic)so even the fastest of vertical velocities is very small.This is not a measure of strong forcing as in a thunderstorm.The measure is done in microbars/second which is close to centimeters per second.,Two main ingredients go into measuring vertical velocities temperature advection and vorticity advection.Warm advection and positive vorticity advection are associated with lift,or rising air.Cold advection and negative vorticity advection are associated with subsidence,or sinking air.,21,The Products Vertical Velocities,Like the other products,we are using the GFS model here.,Areas of rising air,Areas of strong sinking,Also,as with previous maps and slides,the heights and color bar are located on here.,Products like this can be found on most models and at many layers such as 500mb,700mb,and 850mb.The default,or standard layer,is usually at 700mb for this product.,22,The Products-Temperatures,There are three main types of temperature products found on most model outputs.,Basic air temperatures(T),Wet-bulb temperatures(T,w,)used for precipitation type.,Theta-e(,e,)a measure of total heat(basically a combination of air temperature and moisture),23,The Products-Temperatures,GFS(in this case),Surface(2 meter)temperatures,Mean sea level pressure,Highs and Lows,Wind barbs,You can find fronts,troughs,and ridges,Tropical systems,too,H,L,L,L,All models have some form of temperature forecast plot.Generally you will find this for the mid and low levels(500,700,850,925)and the surface.,24,The Products Temperatures(Theta-e),Cool and dry air advecting southward,Southeasterly winds,advect warmer and more moist air,An understanding theta-e is more,easily attainable when one has studied soundings and the concept of parcels.What one should realize,though,is that theta-e is a measure of the total heat.The higher the value of theta-e(measured in Kelvin in this picture)the higher the heat content.In this picture to the right it is easy to see that a very cool,dry,continental air mass is taking hold of the Great Lakes region.,It is important to note that theta-e values are often detailed at the surface,850mb(as in this picture),and 700.For severe weather,we look for theta-e to decrease with height.In other words,very warm/moist at the low levels and much cooler/dryer air aloft.,Concepts of theta and theta-e also involve motions of air such as isentropic lift.We encourage all students to look further into these concepts on their own(or in a class!),25,Moisture Parameters,Relative Humidity generally done for upper air products,250mb-850mb.,Dewpoints generally done for the lower layers of the atmosphere(850mb,925mb)and near the surface.,26,Moisture Parameters-RH,Relative Humidity plots are done all upper levels of the atmosphere.,250 One might look for areas of RH to see where thick cirrus is being forecast,500 and 700 The model worlds version of looking at a water vapor satellite.One can see dry intrusions,areas of vertical ascent and subsidence.And a careful observer can note areas of convection blowing up within a dry intrusion.,850 and 925 Forecasters can use this to see areas of thick stratus and warm advection as well as general areas of vertical motion(which creates or impedes cloud development.),Streamlines,a snapshot of the wind flow,are also plotted along with the RH to help the user in the analysis.,27,Moisture Parameters Dewpoint,Dewpoint temperatures(T,d,)are generally plotted for the lower levels of the atmosphere such as 850mb to the surface.,Surface dewpoint plots can be calculated in different ways of which the user needs to be aware.Here at COD,we do it two ways.,2m T,d,The“skin”layer of the surface.This is the model prediction of what the surface observations will record the dewpoint to be at each hour.,0-30mb T,d,An average dewpoint of the lowest 30mb.This takes into account some mixing that goes on in the lowest part of the boundary layer.,Do not be surprised to see other parameters plotted along with the dewpoints such as streamlines,wind barbs,lifted indexes,C.A.P.E,etc.Dewpoint temperatures plots are vital to severe weather forecasting hence the severe weather overlay plots and wind plots.,Dewpoints are also very important in winter forecasting,temperature forecasts,general forecasting(clouds,etc.),among other things.,28,Moisture Parameters Dewpoint,This is a great example of“moisture return”.At image one(at 12Z Nov 20)one can observe a surface high pressure sitting along the coast of Louisiana and Texas.This is noted by the anticyclonic(clockwise)flow of air.With time,this high pressure moves to the east,allowing the southerly flow on the back side of the high to bring moisture from the Gulf of Mexico back into the eastern half of the US.,29,Thicknesses and Precipitation,Most sites that provide model data,including here at NEXLAB,tend to display thickness plots with a QPF(Quantitative Precipitation Forecast)overlay.,What is thickness?,To properly understand thickness plots,students are encouraged to further look into the hypsometric equation.A basic understanding is as follows:“The thicker the warmer”.Air expands when it is heated,and the atmosphere responds accordingly.Higher thickness values mean a higher average temperature within that layer.,A standard thickness plot is done for the 1000 500mb layer.However there are many others and can be seen on our models page.,The“540”line is a first guess,rule of thumb,for rain vs.snow.540 is short for 5400 meters.That can,often,represent the thickness associated with an average temperature from 1000-500mb that is cold enough for snow or ice.But beware it is not very precise.,What is QPF?,Be careful to understand that precipitation forecasts are based on precipitation that,has fallen,and,not,precipitation that,is falling,!,The precipitation plot is for precip that has fallen either for the previous 3 or 6 hours.Be aware of which one you are looking at!,Just because a model says it will have precip doesnt mean it will have it.Model world does not equal reality.Models are tools,not gospel!Do not get caught up in looking at QPF and basing your forecast completely on those plots.They are good indicators but not perfect prognostications.,30,Thicknesses and Precipitation,QPF along with color bar.,1000-500mb thicknesses,The“540”line(5400 meter thickness)is solid yellow,31,Using thicknesses to forecast,There are 6 thicknesses plotted,as well as the 850mb,0 degree line.,Also the average RH from 850-500mb.,Each thickness rule of thumb rain vs.snow involves a different slice of the troposphere.,Again,line is based on statistics that say“given this thickness,for this particular layer,the average temperature generally produces wintry precipitation.”.,This is NOT the same as doing an analysis and not absolute fact.This is only one of many tools for rain vs snow.,32,Instability and Shear Products,Many of these products involve a more in depth understanding of meteorology.,However,limited knowledge of these products can allow a user to at least get a feel for the severe weather conditions possible.,One is encouraged to further study severe weather paramaters such as shear,instability,sounding analysis,hodographs,and other severe weather analysis tools and concepts.,33,Instability and Shear Products,Instability products how fast can air rise?,Convective Available Potential Energy(CAPE)Measure in Joules of energy per Kilogram of air.The higher the number,the more unstable.Usually ranges from 25(very low)to 5 or 6 thousand(very high).,(SBCAPE)Surface Based air lifted upward from the ground,(MLCAPE)Mixed Layer accounts for mixing within the boundary layer,(MUCAPE)Most Unstable(parcel)lifts many parcels from within the boundary layer then gives the value for the most unstable lifted air.,Lifted Index(LI)the difference in the temperature within the cumulus,or thunderstorm,vs.the temperature outside the cloud.The more negative the value,the more unstable.,Lapse Rates or Delta-Ts shows how fast the atmosphere is cooling with height.The higher the number,the faster the atmosphere is cooling off with an increase in altitude.,(CINH)Convective Inhibition how much will the air be