Comparing GPM and CloudSat Products Emphasizes

the Challenge of Observing Snowfall from Space

Lisa Milani (Code 612, NASA/GSFC and UMD); Gail Skofronick-Jackson

(NASA/HQ); Mark S. Kulie (NOAA); Stephen J. Munchak (Code 612,

NASA/GSFC); Norman B. Wood (UW), Vincenzo Levizzani (ISAC-CNR)

The differences between the first stable falling snow retrievals from the Global Precipitation

Measurement (GPM) Core Observatory and CloudSat’s Cloud Profiling Radar (CPR) falling

snow product can be traced to differences in snow-rain classification, sampling, instrument

sensitivity, and algorithm assumptions. After mitigating these quantitative snowfall estimate

methodologies, near-global snowfall differences are reduced to under 20%.

GPM DPR Radar Snowfall Rates CloudSat CPR Radar Snowfall Rates

Combined DPR+GPROF Snowfall Rates GMI GPROF Snowfall Rates

Name: Lisa Milani, NASA/GSFC, Code 612 and UMD

E-mail: lisa.milani@nasa.gov

Phone: 301-614-5703

References:

G. Skofronick-Jackson, M.S. Kulie, L. Milani, S.J. Munchak, N.B. Wood, V. Levizzani, 2019: Satellite Estimation of Falling Snow: A Global Precipitation

Measurement (GPM) Core Observatory Perspective”. J. Appl. Meteor. and Climatol., 58, 1429-1448.

Data Sources: For this work the Global Precipitation Measurement (GPM) Dual-Frequency Precipitation Radar (DPR) precipitation products from the

Normal Scan mode (NS) for Ku Precipitation Radar (PR), the High-Sensitivity Ka scanning mode (HS) and the Matched Scan (MS) for Ka PR and Ku PR

are used, together with the Goddard Profiling Algorithm (GPROF). The GPM combined product (DPR+GPROF) is also used, as well as the CloudSat

Cloud Profiling Radar (CPR) 2C-SNOW-PROFILE product.

Technical Description of Figures:

Graphic: Mean annual snowfall rates as given by GPM DPR (MS) and CloudSat CPR 2C-SNOW-PROFILE (top), Combined (DPR+GPROF) and GPROF

(bottom), from April 2014 to March 2017 on a 1ºx1º grid. Major spatial differences are noticeable over the oceans where DPR detects much more snowfall

than the other products, due to its phase classification method. GPROF underestimates snowfall rates, while 2C-SNOW-PROFILE presents higher rates

thanks to the high sensitivity of the 94GHz radar to snowfall and the consequent low missing rate.

Scientific significance, societal relevance, and relationships to future missions: Retrievals of falling snow from space-based observations represent

key inputs for understanding and linking the Earth’s atmospheric, hydrological, and energy cycles. This work quantifies and investigates causes of

differences among the first stable falling snow retrieval products from the Global Precipitation Measurement (GPM) Core Satellite and CloudSat’s CPR

falling snow product. An important part of this analysis details the challenges associated with comparing the various GPM and CloudSat snow estimates

arising from different snow-rain classification methods, orbits, resolutions, sampling, instrument specifications, and algorithm assumptions. After equalizing

snow-rain classification methodologies and limiting latitudinal extent, CPR observes nearly 10 (3) times the occurrence (accumulation) of falling snow as

GPM’s DPR). The occurrence disparity is substantially reduced if CloudSat pixels are averaged to simulate DPR radar pixels and CPR observations are

truncated below the 8 dBZ reflectivity threshold. However, even though the truncated CPR- and DPR-based data have similar falling snow occurrences,

average snowfall rate from the truncated CPR record remains significantly higher (43%) than the DPR, indicating that retrieval assumptions (microphysics

and snow scattering properties) are quite different. Diagnostic reflectivity (Z) - snow rate (S) relationships were therefore developed at Ku and W band

using the same snow scattering properties and particle size distributions in a final effort to minimize algorithm differences. CPR-DPR snowfall amount

differences were reduced to ~16% after adopting this diagnostic Z-S approach.

Earth Sciences Division - Atmospheres

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Camp Fire

Woolsey Fire

MODIS Camp Fire Paradise

California Fire

(November 9, 2018)

3D-Winds from Low-Earth and Geostationary Stereo ImagingD. L. Wu1, J. L. Carr2, R. E. Wolfe3, H. Madani1, G. Lin4,3 and B. Tan4,3

1. Climate and Radiation Lab (613); 2.Carr Astronautics; 3. Terrestrial Information Systems Lab (619); 4. SSAI

39.6oN

Advanced Image Navigation and Registration (INR) of low-Earth (LEO) and

geostationary orbit (GEO) sensors enables accurate retrievals of atmospheric

motion vector (AMV) and cloud height from LEO-GEO stereo technique, to

study planetary boundary-layer (PBL) dynamics and processes.

GOES-16Camp Fire

Woolsey Fire

Name: Dong L. Wu, NASA/GSFC, Code 613

E-mail: dong.l.wu@nasa.gov

Phone: 301-614-5784

References:

Carr, J. L., D. L. Wu, R. E. Wolfe, H. Madani, G. Lin, and B. Tan (2019), Joint 3D-Wind Retrievals with Stereoscopic Views from MODIS and GOES.

Remote Sens. 2019, 11, 2100; doi:10.3390/rs11182100

Carr, J. L., D. L. Wu, M. A. Kelly, and J. Gong (2018), MISR-GOES 3D Winds: Implications for Future LEO-GEO and LEO-LEO Winds, Remote Sens.

2018, 10(12), 1885; doi.org/10.3390/rs10121885.

Data Sources: Terra and Aqua MODIS L1B and GOES-16 and -17 ABI (advanced baseline imager) were used in this study. Thanks to Marco Concha of

the NASA GOES-R program for providing a mission-life ephemeris for both GOES-R satellites. Thanks also to Diego Principe, NASA/GSFC summer

intern, for running several of the cases presented here.

Technical Description of Figure:

Figure: On November 9th, two large wildfires were burning in California: Camp Fire and Woolsey Fire. Both MODIS and GOES-16 had a clear view of

these fires, but from different viewing angles. The near-simultaneous observations from two different viewing angles allow accurate retrievals of AMV and

cloud/plume height with a stereoscopic imaging technique. The map on the right shows the retrieved MODIS-GOES AMV and height over the northern

California, which captures a moment of rapid development of Camp Fire at 18:55 UTC (11:55 Local Time). The wind speed shows ~5 m/s northwesterly

winds at the top of the plume near the City of Paradise. The leading edge of plume, along the slice west-to-east, has a higher altitude than the trailing edge,

decreasing steadily from 4 km to 2 km. The elevated fire plume (~4 km) is observed over Paradise, suggesting intense burning and heating on the ground.

A wind speed of 22 m/s was reported on the ground on November 9th, allowing the fire to grow rapidly. Because of such rapid development, many

residents in Paradise were unable to evacuate before the fire arrived, and firefighters were unable to prevent the flames from spreading.

Scientific significance, societal relevance, and relationships to future missions: This work demonstrates potential of the stereoscopic imaging

technique for high-accuracy measurements of AMVs and cloud/plume heights. The LEO-GEO stereo technique is applied successfully to the

contemporaneous MODIS and GOES-R series ABI imagery for a case of wildfire plumes in the planetary boundary layer (PBL). The AMV height accuracy

from LEO-GEO stereo technique offers great potential for future PBL science missions as well as for the understanding of atmospheric processes that

requires 3D coverage of cloud dynamics.

The advantages of using MODIS and MODIS-like imagers with GOES are that MODIS offers a wider swath (2330 km) and eight thermal IR bands that pair

well with those of ABI. The 3D-winds retrieval model is based on our previous MISR-GOES work and is universally applicable to LEO–GEO, GEO–GEO,

and LEO–LEO pairings. The LEO-GEO stereo technique require no synchronization between the LEO and GEO observations from heterogeneous

platforms, because the retrieval model accounts for the non-simultaneity by solving the disparities induced by motion and parallax together. The new

methods are enabled by the accurate geolocation provided by modern imaging systems like MODIS and ABI.

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Earth Sciences Division - Atmospheres

Space-Based Observations for Understanding Changes in the Arctic-Boreal Zone:

Recommendations for Improving Upon the Current Observational Network

CABS Article Published in Review of Geophysics

For the last several years, the CABS task group has been working on a Review of

Geophysics article (https://doi.org/10.1029/2019RG000652), led by Bryan Duncan

(614) and Lesley Ott (610.1). Numerous GSFC (610.1, 613, 614, 615, 618) & LaRC

personnel contributed to this effort, as well as, non-NASA scientists from Arctic

nations, including the U.S., Finland and Canada.

The purpose of the article is to review the strengths and limitations of the current

suite of observations from satellites to provide the necessary information to

understand the complex interaction between components of the ABZ. In addition,

we make recommendations for improving satellite observations of individual

components of the ABZ and for an interdisciplinary and stepwise approach to

develop a comprehensive ABZ Observing Network (ABZ-ON).

Changes in the Arctic-Boreal System (CABS)

In 2014, Doug Morton (618), with enthusiastic support from Piers Sellers, initiated

the CABS task group at GSFC to encourage inter-disciplinary research at GSFC on

Arctic-Boreal Zone (ABZ) issues.

Recommendations of CABS Article

We recommend continuation of the capabilities of the currently operating

instruments, to extend the long-term records, and augmentation of these records

with data from new instruments, such as lidars that provide their own light source, an

advantage in the often low light conditions of the ABZ (see Table 1 of article).

Among the observational needs that we ranked as being most important are those

associated with gaining a process-based and large-scale understanding of the ABZ

carbon cycle and hydrologic cycle (which includes sea level rise) as they have the

potential to affect a large portion of Earth’s population via economic loss,

displacement, etc. For example, these carbon cycle observational priorities include

atmospheric concentrations of methane and carbon dioxide and also the factors that

are necessary to infer their emission source strengths, such as from wetlands,

permafrost, and wildfires.

Next Steps for CABS

Now that the article is accepted for publication, the CABS task group will explore

ways to act upon those recommendations outlined in the Review of Geophysics

article. Everyone is welcome to join us in charting our path forward. Please

contact Bryan.N.Duncan@nasa.gov or Lesley.E.Ott@nasa.gov.

Figure. The Arctic Boreal Zone (ABZ) has complex and often poorly understood interactions

between the cryosphere, biosphere, hydrosphere, and atmosphere. A change in one process

often triggers changes and feedbacks in numerous interconnected processes (e.g., polar

amplification). Figure reproduced from Figure 1 of Hinzman et al. (2013), Copyright © 1999-

2019 John Wiley & Sons, Inc. All rights reserved.

Contact: Paper led by Bryan N. Duncan and Lesley E. Ott

Bryan.N.Duncan@nasa.gov; Lesley.E.Ott@nasa.gov

Reference: Bryan N. Duncan, Lesley Ott, (in alphabetical order) James B. Abshire, Ludovic Brucker, Mark L. Carroll, James Carton, Josefino C. Comiso,

Emmanuel P. Dinnat, Bruce C. Forbes, Alemu Gonsamo, Watson W. Gregg, Dorothy K. Hall, Iolanda Ialongo, Randi Jandt, Ralph A. Kahn, Alexey

Karpechko, Seiji Kato, Stephan R. Kawa, Timo Kumpula, Erkki Kyrölä, Tatiana V. Loboda, Kyle C. McDonald, Paul M. Montesano, Ray Nassar, Christopher

S. R. Neigh, Claire L. Parkinson, Benjamin Poulter, Jouni Pulliainen, Kimmo Rautiainen, Brendan M. Rogers, Cecile S. Rousseaux, Amber J. Soja, Nicholas

Steiner, Johanna Tamminen, Patrick C. Taylor, Maria A. Tzortziou, Henrik Virta, James S. Wang, Jennifer D. Watts, David M. Winker, and Dong L. Wu,

Space-Based Observations for Understanding Changes in the Arctic-Boreal Zone, accepted to Review of Geophysics. https://doi.org/10.1029/2019RG000652.

Detailed Summary: Observations taken over the last few decades indicate that dramatic changes are occurring in the Arctic-Boreal Zone (ABZ), which are

having significant impacts on ABZ inhabitants, infrastructure, flora and fauna, and economies. While suitable for detecting overall change, the current capability

is inadequate for systematic monitoring and for improving process-based and large-scale understanding of the integrated components of the ABZ , which

includes the cryosphere, biosphere, hydrosphere, and atmosphere. Such knowledge will lead to improvements in Earth system models, enabling more accurate

prediction of future changes and development of informed adaptation and mitigation strategies. In this article, we review the strengths and limitations of current

space-based observational capabilities for several important ABZ components and make recommendations for improving upon these current capabilities. We

recommend an interdisciplinary and stepwise approach to develop a comprehensive ABZ Observing Network (ABZ-ON), beginning with an initial focus on

observing networks designed to gain process-based understanding for individual ABZ components and systems that can then serve as the building blocks for a

comprehensive ABZ-ON.

Scientific significance, societal relevance, and relationships to future missions: The Arctic Boreal Zone (ABZ) is the region that lies north of approximately

50°N and includes the boreal, sub-Arctic, and Arctic climate zones. There are complex and often poorly understood interactions between the cryosphere,

biosphere, hydrosphere, and atmosphere of the ABZ, which currently limit our ability to predict future ABZ changes in a globally warmer world. ABZ changes

may have profound negative impacts for humans far beyond the ABZ, such as by exacerbating global warming through the release of vast amounts of carbon

stored in frozen soils and raising sea levels via melting of land ice, especially on Greenland. Observations of the ABZ taken from the surface, aircraft,

Unmanned Aerial System (UAS), balloon, and boat are sparse and expensive to collect in the often inaccessible and inhospitable environment. While these

suborbital data have been invaluable, they lack the far more complete, repeat spatial coverage that Earth-observing satellites uniquely provide, which has

transformed our ability to observe large-scale changes. More accurate predictions will be enabled by a combination of improved models, new satellite

instruments, and an improved data network. In our review, we recommend continuation of the capabilities of the currently operating instruments, to extend the

long-term records, and augmentation of these records with data from new instruments, such as lidars that provide their own light source, an advantage in the

often low-light conditions of the ABZ. Among the observational needs that our review ranked as being most important are those associated with gaining a

process-based and large-scale understanding of the ABZ carbon cycle and hydrologic cycle (which includes sea level rise) as they have the potential to affect a

large portion of Earth’s population via economic loss, displacement, etc. For example, these carbon cycle observational priorities include atmospheric

concentrations of methane and carbon dioxide and also the factors that are necessary to infer their emission source strengths, such as from wetlands, permafrost,

and wildfires. At the same time, a well-developed and more comprehensive ABZ observing network would provide data for a more thorough evaluation of

Earth system model performance and identification of areas where further developments are needed. We need data collected from a wide variety of satellite

instruments, as well as instruments based on aircraft and on the ground. Our review makes recommendations for an interdisciplinary and stepwise approach to

develop a comprehensive ABZ observing network (ABZ-ON).