The Impact of Hail and Large Ice on Multi-Frequency Radar Observations

Gerald Heymsfield, Code 612, NASA/GSFC; Lin Tian, GESTAR, and others

Ku-bandX-band

Ka-band W-band

North Carolina Hailstorms

Four-frequency measurements from GSFC

CRS (W), HIWRAP, and EXRAD radars on the

NASA ER-2

Hail-producing storms induce significant multiple scattering (MS) in radar observations at

frequencies typically used for airborne and spaceborne radars. The four ER-2 bands, ranging from

9.6 GHz to 94 GHz, show that MS contributions get progressively larger at higher frequencies. MS

will artificially increase reflectivity and will therefore will require more sophisticated algorithms for

its detection and for particle retrievals from multi-frequency measurements.

Name: Gerald Heymsfield, NASA/GSFC, Code 612

E-mail: gerald.heymsfield@nasa.gov

Phone: 301-614-6369

References:

Battaglia, A., K. Mroz, T. Lang, F. Tridon, S. Tanelli, G. M. Heymsfield, and L. Tian, 2016: Using a multi-wavelength suite of microwave instruments to

investigate the microphysical structure of deep convective cores. J Geophys. Res. Atmos., 121, 16, 9356-9381. DOI: 10.1002/2016JD025269

Battaglia, A., Simone Tanelli, Gerald M. Heymsfield, and Lin Tian, 2014: The dual wavelength ratio knee: a signature of multiple scattering in airborne Ku–

Ka observations. J. Appl. Meteor. Climatol., 53, 1790–1808. DOI: 10.1175/JAMC-D-13-0341.1

Heymsfield, Gerald M., Lin Tian, Lihua Li, Matthew McLinden, Jaime I. Cervantes, 2013: Airborne Radar Observations of Severe Hailstorms: Implications

for Future Spaceborne Radar. J. Appl. Meteor. Climatol., 52, 1851–1867. DOI: 10.1175/JAMC-D-12-0144.1

Data Sources: The data were collected at four frequencies with the GSFC EXRAD (X band) HIWRAP (Ku/Ka bands), and CRS (W band) radars flying in

a fixed, nadir-looking configuration on the NASA ER-2 aircraft during the Global Precipitation Mission (GPM) ground-validation (GV) Integrated

Precipitation and Hydrology Experiment (IPHEx). The ER-2 flights were jointly funded by GPM GV and the Aerosol, Chemistry, and Ecology (ACE)

mission formulation studies.

Technical Description of Figures:

Left Panels: Nadir vertical sections of four frequencies of radar reflectivity show two intense, hail-producing thunderstorms in North Carolina on 23 May

2014. Multiple scattering (MS) is evident at all frequencies in the core of these storms which contain hail up to 5 cm in diameter. Features that suggest

MS are the nearly constant or increasing reflectivity with decreasing altitude and the lack of surface echoes. The different lines (blue, green, black, and

cyan) in upper left (X-band) panel correspond to the level below which the MS contribution becomes predominant at X, Ku, Ka, and W bands, respectively.

The continuous, dashed, and dotted green lines (Ku, Ka, W bands) correspond to the levels at which the top‐down optical thickness exceeds 1, 3, and 5,

respectively.

Right Figure: Vertical profiles of radar reflectivity are shown for one location in a storm core for the four frequencies. The shaded curves depict the

observed reflectivity profiles. The dotted curves show the calculated single scattering reflectivity based on the assumption of hail, and the diamond symbols

show the calculated reflectivity given the same assumptions, but including MS effects. The shapes of these profiles contain what has been called a “knee”

where the reflectivity, initially decreasing toward the surface due to attenuation and non-Rayleigh scattering (dotted curve), anomalously flattens because

of MS (diamonds) driven by the presence of hail and other large ice particles.

Scientific significance, societal relevance, and relationships to future missions: The findings in this work, and other related papers, are the first

conclusive evidence that multiple scattering can be significant in convective storms with large ice. This includes even the lowest Ku-band frequency on

GPM, and it highlights the deficiencies with using higher frequencies such as Ka band for measuring strong thunderstorms. MS is very difficult to detect

with single frequency spaceborne radars (GPM DPR Ku or Ka bands, CloudSat) because of the large footprints and nonuniform beam filling. Multiple

scattering signatures are now being detected in GPM DPR data, and these effects will be included in future GPM algorithms. Given the high societal

impact of intense thunderstorms and hail, resolving the challenges of interpreting radar data affected by multiple scattering will increase the value of

airborne and spaceborne observations of precipitation. These results are highly relevant to future missions such as Aerosol, Chemistry, and Ecosystems

(ACE) in the previous Decadal Survey, and Clouds, Convection, and Precipitation (CCP) in the 2017 Decadal Survey.

Earth Sciences Division - Atmospheres

DSCOVR EPIC calibration using MODIS and lunar observations

Alexander Marshak, Code 613, Igor Geogdzhayev Columbia University/NASA GISS

DSCOVR’s EPIC instrument, uniquely positioned at the Lagrange-1 point, is an important

addition to the observations from currently operating low Earth orbit observing

instruments. Because EPIC lacks an onboard calibration facility, four EPIC visible and

NIR channels were calibrated via MODIS reflectances. The two EPIC O2 absorbing

channels were calibrated via Lunar observations.

Name: Alexander Marshak, NASA/GSFC, Code 613

E-mail: Alexander.Marshak@nasa.gov

Phone: 301-614-6122

References:

Geogdzhayev, I.V., and A. Marshak, Calibration of the DSCOVR EPIC visible and NIR channels using MODIS Terra and Aqua data and EPIC lunar

observations, Atmospheric Measurement Techniques, 2018 (in press).

Data Sources: DSCOVR EPIC Level 1b data and Level 2 products were obtained from the Atmospheric Science Data Center (ASDC) of the NASA

Langley Research Center (LaRC) by the following link: https://eosweb.larc.nasa.gov/project/dscovr/dscovr_epic_l1b_2. The Terra and Aqua MODIS L1b

data were acquired from Atmosphere Archive & Distribution System (LAADS) Distributed Active Archive Center (DAAC) at Goddard Space Flight Center

(https://ladsweb.nascom.nasa.gov/).

Technical Description of Figures:

Graphic 1: EPIC image (https://epic.gsfc.nasa.gov/?date=2016-12-07) of the entire sunlit Earth hemisphere (right) is compared with the Apollo image

(https://www.nasa.gov/content/blue-marble-image-of-the-earth-from-apollo-17) taken on the same day 44 years ago. The two images show a remarkably

similar large-scale cloud structure.

Graphic 2: To determine the EPIC calibration coefficients two independent methods are used: The first method is based on calculating the linear

regression between EPIC counts and MODIS reflectances in the closest MODIS spectral channel for the most homogeneous scenes; the second method

relies on finding the mean MODIS / EPIC (M/E) ratio for bright homogeneous scenes. The graphic illustrates the first method. It shows scatter plots of

MODIS reflectance vs. EPIC counts in four spectral channels for the most homogeneous matching scenes and the corresponding regression lines.

Matches between June 2015 and March 2017 are used. Also shown are correlation coefficient R and the number of points used for the regression. The

colored marks and the dashed lines correspond to data without spectral correction, while the black marks and solid lines include spectral correction.

Scientific significance, societal relevance, and relationships to future missions: EPIC’s position at the L1 point and unique observational geometry

makes it an important complement to LEO remote sensing instruments. Measurements in the backscattering region allow observations and

characterizations of the glint caused by oriented ice crystals in clouds, and also facilitate better vegetation monitoring. Moreover, the EPIC instrument

offers an improved temporal sampling compared to instruments on sun-synchronous orbits, with the entire sunlit hemisphere being sampled 10–20 times

per day. It thus has the potential to augment remote sensing observations in such applications as determination of aerosol, cloud, sulfur dioxide, and ozone

amounts, as well as vegetation properties. Radiometric calibration of the measurements is a required first step for many of the above applications.

Because the EPIC instrument does not have in-flight calibration capabilities, it is necessary to determine the calibration coefficients and monitor their

stability by means of vicarious calibration.

Earth Sciences Division - Atmospheres