# Presentation: 158178

## UltraViolet Index

**Craig S. Long**
***National Oceanic and Atmospheric Administration***
***National Weather Service***
***National Centers for Environmental Prediction***
***Climate Prediction Center***

## Outline

***Background information on UV radiation***
***Factors that affect UV radiation***
***Health effects***
***History of UV Index***
***WMO/WHO Standards***
***NWS UV Index Algorithm***
***Current***
***Future***
***Products***

## Background

***Definition:***
***UV Index is a scaled erythemal (skin reddening) dose rate integrated over the UV-B and UV-A spectral bands.***
***WMO guidelines require forecasts to be generated at least for next day at solar noontime.***

## Background

***UltraViolet radiation has shorter/more powerful wavelengths than visible light.***
***The most dangerous wavelengths of UV spectrum (UV-C) are ***_***completely***_*** absorbed in the stratosphere.***
_***Partial***_*** absorption of UV-B***
_***Minor***_*** absorption of UV-A***

## UV Health Effects

***Short Term overexposure to UV-B:***
***UV-B causes sunburn (erythema)***
***Sunburn can prevent your body from eliminating heat efficiently and can contribute to heat stress***
***Long Term overexposure to UV-B:***
***Several severe sun burns linked to melanoma***
***One person dies of skin cancer per hour in the U.S.***
***Sustained exposure linked to squamous and basal skin cancers – non lethal***
***Cataracts of eyes****** ***
***Long Term overexposure to UV-A:***
***Aging of skin***
***Loss of elasticity (leathery look)***
***Small amounts of UV radiation needed for Vitamin-D***

## UV Health Effects

_**UV Health Effects**_

## Background

***Factors affecting UV radiation from TOA to surface:***
***Flux at TOA***
***Earth – Sun distance***
***Ozone (total column)***
***Solar Zenith Angle***
***Latitude, Day of Year***
***Clouds***
***Aerosols***
***Elevation***
***Surface Albedo***
***No Snow***
***Snow***

## 1980’s: Australia started reporting yesterday’s UV radiation levels in conjunction with huge sun protection campaign.
1992: Environment Canada began issuing a next day forecast of clear sky UV levels called ‘UV Index’.
1994: NWS and EPA begin issuing a next day forecast w/cloud effects.  Use slightly different scale than Canadians.  Allowed to use name ‘UV Index’.
1995: WMO holds “meeting of experts” to establish UV Index definition.
1997: WMO holds second “meeting of experts” to standardize UV Index name and forecasts
2000: WHO holds meeting to standardize health messages and exposure categories.

***1992:****** Environment Canada began issuing a next day forecast of clear sky UV levels called ‘UV Index’.***
***1994: ******NWS and EPA begin issuing a next day forecast w/cloud effects.  Use slightly different scale than Canadians.  Allowed to use name ‘UV Index’.***
***1995:****** WMO holds “meeting of experts” to establish UV Index definition.***
***1997:****** WMO holds second “meeting of experts” to standardize UV Index name and forecasts***
***2000:****** WHO holds meeting to standardize health messages and exposure categories.***

_**History**_

## UV Index Definition

***UV Index****** is a scaled erythemal dose rate integrated over the UV-B and UV-A spectral bands.***

## UV Spectrum

_**UV Spectrum**_

## Weighted Irradiances

_**Weighted Irradiances**_

## EDR = Integral over the 290 to 400 nm range
EDR = ~0.250 Watts/m2 or 250 mW/m2.
Erythemal Dose Rate is the instantaneous flux of skin reddening UV radiation.
UV Index is the EDR(W/m2) x 40.
Or EDR(mW/m2)/25
UV Index = 10.0

***EDR = ~0.250 Watts/m******2****** ******or 250 mW/m******2******.***
***Erythemal Dose Rate is the instantaneous flux of skin reddening UV radiation.***
***UV Index is the EDR(W/m******2******) x 40.***
***Or EDR(mW/m******2******)/25***
***UV Index = 10.0***

_**Erythemal Dose Rate**_

## RTMs are needed to determine “clear sky” UV flux at surface under prescribed conditions.
SZA 
Ozone 
Aerosols 
Elevation
Albedo
Several types of RTMs:
multiple scattering spectral models
fast spectral models
empirical models 
RTMs are computationally expensive
Operational forecasts of large gridded fields require the creation of Look Up Tables 

***SZA ***
***Ozone ***
***Aerosols ***
***Elevation***
***Albedo***
***Several types of RTMs:***
***multiple scattering spectral models***
***fast spectral models***
***empirical models***
***RTMs are computationally expensive***
***Operational forecasts of large gridded fields require the creation of Look Up Tables ***

_**Radiative Transfer Models**_

## Results from Spectral Radiative Transfer Model

_**Results from Spectral Radiative Transfer Model**_

**Ozone Hole**

**Tropics**

**Extra Tropics**

## Zonal Mean Ozone

_**Zonal Mean Ozone**_

## Zonal Mean UV Index (clear sky, sea level, no aerosol)

_**Zonal Mean UV Index (**__***clear sky, sea level, no aerosol***__**)**_

## Current UV Fcst
Ozone Forecast from GFS
Albedo = 5% (no snow)
Elevation (6% per Km)
Aerosol – clean atmosphere
     (AOD=0.2, SSA=1.0)
Clouds amounts from MOS
Products:
58 city bulletin
Clear sky UV Index on global 1x1 grid
Cloudy UV Index for CONUS and AK grids

***Ozone Forecast from GFS***
***Albedo = 5% (no snow)***
***Elevation (6% per Km)***
***Aerosol – clean atmosphere***
***     ******(AOD=0.2, SSA=1.0)***
***Clouds amounts from MOS***
***Products:***
***58 city bulletin***
***Clear sky UV Index on global 1x1 grid***
***Cloudy UV Index for CONUS and AK grids***

_**UV Index Forecast**_

***Future UV Fcst***
***Ozone Forecasts from GFS***
***Albedo ***
***no snow = 3%***
***Snow = >30% (GFS Albedo)***
***Elevation***
***9% 1******st****** km***
***7% 2******nd****** km***
***6% 3******rd****** km***
***Aerosol***
***Variable from climatology***
***Cloud attenuation from GFS shortwave code ***
***Products:***
***58 city bulletin***
***Global Cloudy and Clear Sky grids***

## 3 Forecasts in one
Ozone Forecast
Cloud Forecast
Aerosol Forecast (not there yet)

_**UV Index Forecast**_

***3 Forecasts in one***
***Ozone Forecast***
***Cloud Forecast***
***Aerosol Forecast (not there yet)***

## NCEP GFS Ozone Assimilation

_**NCEP GFS Ozone Assimilation**_

## Global Ozone Field

_**Global Ozone Field**_

***Ozone Hole***

## Global UV Index

_**Global UV Index**_

## Elevation Effect

_**Elevation Effect**_

***Binghamton, NY***

***Lubbock, TX***

***Boulder, CO***

***Jackson, WY***

***Yellowstone, WY***

***Breckenridge, CO***

## Surface has low albedo is UV ~ 3%
Sand is more reflective ~30%
Snow is most reflective ~30-90%

***Sand is more reflective ~30%***
***Snow is most reflective ~30-90%***

_**Albedo **_

## Albedo (snow and sand) 

_**Albedo (snow and sand) **_

## Aerosols scatter and absorb UV radiation
Reduce direct and Increase diffuse
Global is usually attenuated
Aerosol parameters include:
Aerosol Optical Depth
Single Scattering Albedo
Ratio of scattered /(scattered + absorbed)
Asymmetry factor 
Forward scattering vs backward scattering

***Reduce direct and Increase diffuse***
***Global is usually attenuated***
***Aerosol parameters include:***
***Aerosol Optical Depth***
***Single Scattering Albedo***
***Ratio of scattered /(scattered + absorbed)***
***Asymmetry factor****** ***
***Forward scattering vs backward scattering***

_**Aerosol Effects**_

## Aerosol Optical Depth

Single Scattering Albedo 

**Single Scattering Albedo**

_**Aerosol Climatology**_

## Aerosol Effect

_**Aerosol Effect**_

## Current Method: MOS clouds 
MOS fcsts Pct Clear, Scattered, Broken, Overcast
Regression determined by comparing MOS fcsts against observed cloud transmission
Clear (0-1 tenths): 	100% transmission
Scattered(2-5 tenths):	89%
Broken(6-8 tenths): 	72%
Overcast(9-10 tenths): 31%
Proposed Method: From GFS Shortwave scheme
UV Transmission = UVCloud/UVNo Cloud

_**Cloud Forecasts**_

***Current Method: MOS clouds****** ***
***MOS fcsts Pct Clear, Scattered, Broken, Overcast***
***Regression determined by comparing MOS fcsts against observed cloud transmission***
***Clear (0-1 tenths): ******	******100% transmission***
***Scattered(2-5 tenths):******	******89%***
***Broken(6-8 tenths): ******	******72%***
***Overcast(9-10 tenths): 31%***
***Proposed Method: From GFS Shortwave scheme***
***UV Transmission = UV******Cloud******/UV******No Cloud***

## UV Attenuation from GFS Clouds

_**UV Attenuation from GFS Clouds**_

## Clouds and UV Attenuation

_**Clouds and UV Attenuation**_

## Clouds and UV Attenuation

_**Clouds and UV Attenuation**_

## Clouds and UV Attenuation

_**Clouds and UV Attenuation**_

## Clouds and UV Attenuation

_**Clouds and UV Attenuation**_

## Clouds and UV Attenuation

_**Clouds and UV Attenuation**_

## Products: MOS Locations for CONUS and AK

_**Products: MOS Locations for CONUS and AK**_

## Products: 58 City Bulletin

_**Products: 58 City Bulletin**_

## Products: Cloudy UV Index Output Grids

_**Products: Cloudy UV Index Output Grids**_

- Eta Grid 207

- Eta Grid 211

## Products: UV Index Contoured Map

_**Products: UV Index Contoured Map**_

## Products: Global UV Index

_**Products: Global UV Index**_

## UV Index “to do” list

_**UV Index “to do” list**_

***Generate and validate global noon time UV Index fcsts***
***EMC must operationally output UV******cloud****** and UV******no-cloud****** surface fluxes***
***Generate UV Index forecasts out to day 5***
***Generate UV Index forecasts at both 00Z and 12Z cycles ***
***Generate daily UV dosage***
***Diurnal variation***

## fini

***fini***