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TAIWIN - ('Terminal Area Icing Weather Information for NextGen') In-Flight Icing Operation 

-Also known as RadIA- ('Radar Icing Algorithm')



TAIWIN (Terminal Area Icing Weather Information for NextGen) is a project driven by the FAA to address ground and in-flight icing, where NCAR is currently a contractor on the project.

The purpose of this wiki is to post relevant case studies for the prototype TAIWIN capability.  RadIA was made to run in real-time on a dedicated server for the Cleveland, Ohio NEXRAD during the summer of 2014.

RadIA is now running in real time at Denver , Colorado NEXRAD during the winter of 2015-2016.

This page is maintained by Reid Hansen ( and Dave Serke (

How to interpret RadIA output

The final output of RadIA are color coded as displayed in the color bar below.  Pixels in the radar volume with colors salmon through purple on the left side of the color bar are determined to contain significant in-flight icing, with the type of icing shown in the respective abbreviation.  The scientific reference for each category are shown below and detailed in the reference section.

Tools for In-Flight Icing Diagnosis

Winter 2015-2016, Boulder Field Campaign

Winter 2014-2015 Collaboration Page

RadIA Case Studies for Winter 2014-2015

April 23rd, 2015 - 1 sonde

April 7th, 2015 - 2 sondes

March 26th, 2015 - 3 sondes

March 25th, 2015 - 3 sondes

March 20th, 2015 - 2 sondes

March 17th, 2015 - 2 sondes - sondes hit LWC max

March 13th, 2015 - 3 sondes

March 3rd, 2015 - 0 sondes - FZRN

February 11th, 2015 - 2 sondes - SEV PIREP

February 4th, 2015 - 2 sondes

January 29th 2015 - 2 sondes - FZLevel near sfc, good LWC

January 22nd, 2015 - 1 sondes - Hi ZDR top scavengeing SLW

        * SLW-sonde launches begin

January 9th, 2014

January 8th, 2015

January 6th, 2015

December 18th, 2014

December 10th, 2014

December 3rd, 2014

November 17th, 2014

         * Issue with use of default model temperature profile found and fixed.  Reprocessing of cases prior to this date required to obtain proper RadIA hazard output.

November 13th, 2014

November 7th, 2014

November 1st, 2014

October 31st, 2014

October 20th, 2014

        * Issue with FRZDRZ plotting found and fixed

October 7th, 2014

        * RadIA case analysis begins in early October 2014

        * 'IHL2' field with MIXPHA and PLATES output begins in late September 2014

        * Real-time RadIA output at Cleveland begins in August 2014


List of NASA Glenn Research Facility SLW-Launch times:

20150122 - 14:17:33
20150129 - 19:25:09
20150204 - 13:42:00
20150204 - 17:07:56
20150211 - 20:00:12
20150211 - 21:10:39
20150311 - 14:52:42
20150313 - 20:43:20
20150313 - 21:59:46
20150313 - 23:38:23 
20150317 - 13:54:27
20150317 - 14:47:14
20150320 - 15:00:16
20150320 - 15:49:24 
20150325 - 12:22:36
20150325 - 14:18:06
20150325 - 15:01:35
20150326 - 15:07:53
20150326 - 15:51:14
20150326 - 16:59:37
20150407 - 12:56:38 
20150407 - 14:35:33

NIRSS Test Bed Cases @ Cleveland, Ohio

RadIA and NIRSS wiki from 2012-2013



Aircraft Icing


Rime Ice forms when small super cooled liquid water (SLW) comes in contact with a surface which is at sub-zero celcius. Freezing instantaneously to the object. (usually the leading edge of an airfoil, or the front of the fuselage) Rime Icing takes place more often during colder temperatures (-15C to -20C). Small drops start to accrete on the leading edge of the wing, the freezing air traps cold air and forms an opaque / milky colored ice. Rime Icing is generally regarded as the lease severe icing event due to ice accretion on the leading edge of the airframe, where icing counter-measures are installed. Rime Ice also doesn't disturb the airflow around the airfoil.

Below is an example of Rime Ice accreting on an airfoil.





Clear Ice, the most dangerous form of In-Flight Icing, forms when an aircraft flies through clouds with high concentrations of Supercooled Large Drops (SLD). Due to their size, these drops do not freeze instantaneously when coming in contact with the aircraft. Rather, they gradually freeze as they travel along the aircraft (Either along the airfoil, or the fuselage). Clear Ice is harder to report because it accretes clear. Since Clear Ice travels down the wing, normal de-icing measures can't be implemented. Clear Ice generally occurs around 2C to -10C.


Below is an example of Clear Ice accreting on an airfoil



Mixed phase icing is a combination of Clear Ice and Rime Ice, occurring at temperatures around -10C to -20C. Mixed Phase Icing can form rapidly when ice particles become embedded in clear ice and build a very rough accumulation.

The OWLeS Project

The TAIWIN project is working with the OWLeS (Ontario Winter Lake-effect Systems) in testing of the TAIWIN system.  "The OWLeS project aims to examine the formation mechanisms, cloud micro physics, boundary layer processes and dynamics of lake-effect systems, through the deployment of an array of atmospheric sensors around Lake Ontario in the winter of 2013-2014. OWLeS is a collaborative project involving universities within the region and across the US, as well as the Center of Severe Weather Research and NOAA. OWLeS is supported by the National Science Foundation. Specifically, NSF is supporting two collaborative proposals, one focusing on short-fetch bands under northerly wind (PI: Kristovich) and another focusing on long-fetch bands under westerly wind (PI: Geerts), and a third proposal from the University of Utah (PI: Steenburgh). The latter examines orographic effects of lake-effect snow, over the Tug Hill plateau." (

The SLWC -sonde

No single instrument has yet been developed which can remotely and unambiguously detect in-flight icing conditions within a volume of airspace. Combinations of ground based remote senors and/or numerical weather prediction models have been under development for some time to detect in-flight icing.  These algorithms need to be verified against in-situ data to gain acceptance in the aviation safety community, so either expensive research flights need to be conducted, or comparisons to subjective pilot reports of icing need to be made. This new avenue of verification has come built on the grounds of the Hill and Woffinden (1980) vibrating wire sonde for measurement of SLW content (SLWC) along a weather balloons trajectory has been under development by Anasphere Inc (


OWLeS Test Bed


Graphics generation with Vizmet

The radiometer display on the above case studies was generated by the Vizmet program.  Vizmet generates plots based upon time histories of surface temperature, pressure, and humidity, vertical pointed infrared radiometer measured cloud base temperature, and the microwave radiometer's neural net output of temperature, humidity, and liquid water profiles.  For the NASA Glenn Icing Remote Sensing project plots, Vizmet further refines the neural net profile data by applying the following threshold values:
-Cloud Top: Cloud top limit temperature:   253K
                    Relative Humidity threshold:  70%
-Cloud Base: Ignore Infrared radiometer data
                     Relative Humidity threshold:  80%
-Max values:  RH: 100%
                      Liq:  3 g/m3
-Retain Liquid Cloud shape from neural net





Reference Section

A new SLWC-sonde (Serke et al., 2014) : AMSSMOI_2014_extabs_v2.pdf

Supercooled liquid water (Plummer et al., 2009): ATM_352_ext_abs.pdf

Freezing Drizzle (Ikeda et al., 2008): 2008jamc1939%2E1.pdf

Mixed Phase / Plate Crystals (Williams et al., 2010): sellis_eradposter_icing_2012.pptx

Images of Ice accretion courtesy of NASA Lewis Research Center:

Image of Clear ice formation courtesy of SKYbrary:

Draft of 2015 midyear report to the FAA: click here




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