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Global Modeling and Assimilation Officegmao.gsfc.nasa.govGMAO

National Aeronautics and Space Administration

A13M-08: Global assimilation of X Project Loon stratospheric balloon observations

Lawrence Coy Science Systems and Applications, Inc. Mark R Schoeberl Science and Technology Corporation

Steven Pawson NASA Goddard Space Flight Center Salvatore Candido Project Loon, X Robert W Carver Project Loon, X

Question: Is the current conventional and satellite observation network sufficient to characterize the winds in the lower stratosphere? In this presentation, we add independent wind observations derived from constant pressure balloons to a state-of-the-art data assimilation system and evaluate improvements (if any) to forecasts and analyses.

https://ntrs.nasa.gov/search.jsp?R=20180000629 2020-07-02T15:11:56+00:00Z



Project Loon

Project Loon is a network of stratospheric balloons, designed to extend Internet connectivity to people in rural and remote areas worldwide.

Goal: launch and maintain a fleet of balloons to provide Internet coverage to users on the ground.Autolaunchers: capable of safely and consistently launching a new balloon every 30 minutes. Status: over 25 million km of test flights since the project began.Duration: up to 190 days in the stratosphere.

ConnectionHigh speed internet: transmitted up to the nearest balloon from a telecommunications partner on the ground, relayed across the balloon network, and then back down to users on the ground. Status: demonstrated data transmission between balloons over 100 km apart in the stratosphere and back to the ground with connection speeds of up to 10 Mbps, directly to LTE phones.

https://x.company/loon/



Project LoonNavigatingPower: Solar panels for day with re-chargeable battery for night.Tracking: GPSAltitude: approximately 20 km (60-50 hPa) Altitude Adjustment: capability to move each balloon up or down into different winds enabling the balloons to provide coverage where it’s needed.

RecoveryCoordination: with the local air traffic control to bring balloons to ground in sparsely populated areas. Descent: parachuteCleanup: equipment collected for reuse and recycling.

https://x.company/loon/



Data AssimilationNASA MERRA-2 Data Assimilation System (DAS)Data Assimilation Combines:

1) a global forecast model with 2) observations

to produce the analysis, a complete representation of the global atmosphere at a given time.

MERRA-2 DAS cycles with a six-hour data window, collecting all the observations (~ 5 million, including satellite based radiances and cloud tracked winds, rawindsondes, aircraft, etc.) within six hours of the analysis time.

Data Window Data Window Data Window Data Window Data WindowForecast Forecast Forecast Forecast Forecast

Analysis Analysis Analysis Analysis Analysis

Time à



MethodologyTime Period: June, July, August 2014This test assimilation period was chosen because there were a large number of Southern Hemisphere Loon launches during this time.

We ran two data assimilation system (DAS) experiments, identical, except that one includes the Loon observations and the other does not. Having these two runs, “without Loon” and ”with Loon”, and differencing output, we can assess the changes.

Loon Experiment (with Loon winds)

Full DAS incorporating the Loon observations in the analysis. Loon winds are treated as conventional rawinsondewinds. Winds are interpolated to Loon balloon locations for comparison.

Control (without Loon winds)

Full DAS but does not include the Loon observations in the analysis. Winds are interpolated to Loon balloon locations for comparison.

Using the DAS Interpolation enables a consistent comparison of the Control assimilation winds with the balloon observations.



Longitude Latitude DistributionNumber of Loon Observations (Jun-Aug 2014) per 1ox1o grid box

> 1000500--1000300--50050--3005.--50



Latitude Altitude Loon Balloon DistributionNumber of Loon Observations (Jun-Aug 2014) per 1ox 250 m grid box

-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90Latitude

18

19

20

21

22

23

24

Pres

sure

Alti

tude

(km

)

70

60

50

40

Pres

sure

(hPa

)

> 20001000--2000500--1000100--50010--100

Loon pressures peak at 65 hPa and 55 hPa



Tropical Loon Trajectories (14 Days)

Tropical Coverage in June 2014 Light Red: trajectory startDark Red: trajectory end

Tropical observations provided some of the largest DAS adjustments when assimilating the Loon winds.

This Loon trajectory will be examined in more detail later.



Sample Analysis Wind IncrementsU inc (ms-1) loon 20 Jun 2014 00UTC

52.0 hPa 22 loons

V inc (ms-1) loon 20 Jun 2014 00UTC52.0 hPa 22 loons

a

b

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8 9 10

Example of the data assimilation wind increments. The assimilation increment fields are the difference between the background forecast and the current analysis. Loon locations are indicated as red +.

The contoured field is the difference between the Loon Experiment and the Control, so that only the effects of the Loon data assimilation are seen in the analysis increment differences.

Data assimilation spreads the point observations in the horizontal and vertical domains.



Sample Analysis Wind IncrementsU inc (ms-1) loon 20 Jun 2014 00UTC

52.0 hPa 22 loons


a

b

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8 9 10

This shows how far the zone of influence can extend from the assimilation of the Loon wind observation.

U inc (ms-1) loon 20 Jun 2014 00UTC52.0 hPa 22 loons


a

b

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8 9 10

-4 m/s3 m/s

Close-up View



Sample Analysis Wind Increments (Vertical Structure)

-180 -90 0 90 180Longitude

1000

100

10

Pres

sure

(hPa

)U inc (ms-1) loon 19 Jun 2014 18UTC

5.o Latitude 14 loonsa

-180 -90 0 90 180Longitude

1000

100

10

Pres

sure

(hPa

)

V inc (ms-1) loon 19 Jun 2014 18UTC5.o Latitude 14 loons

b

Example of the data assimilation wind increments. The assimilation increment fields are the difference between the background forecast and the current analysis. Loon locations are indicated as red +.

The contoured field is the difference between the Loon Experiment and the Control, so that only the effects of the Loon data assimilation are seen in the analysis increment differences.

The vertical influence is typically located between 100 and 30 hPa.

Loon Locations

Loon Locations

30 hPa

30 hPa

100 hPa

100 hPa


National Aeronautics and Space Administration Tropical Launch June 2014

Loon Experiment Analysis Winds: Arrows line up with balloon trajectory. Significant differences in indicated regions

Detail about one balloon launched from Brazil on 6 June 2014

Red Curve: Balloon Trajectory

Blue Loon Trajectory denotes Loon altitude lowered from ~50 to ~60 hPa (10-11 June)

Control Analysis Winds: Wind arrows do not line up with the trajectory, indicating a difference from Loon observations.

Blue Arrows: Analyzed Winds Control

With Loon



Tropical Launch June 2014 Zonal Wind Comparison

Altitude Changes

Analysis winds interpolated by the DAS in space and time to the Loon position

Loon Obs and Loon Experiment agree well.

Large differences occur between the Control (Red) and Loon Obs (Black).

Loon ExperimentControl

U



Tropical Launch June 2014Meridional Wind Comparison

Altitude Changes

Analysis winds interpolated by the DAS in space and time to the Loon position

Loon Obs. and Loon Experiment agree well.

Large differences occur between the Control (Red) and Loon Obs. (Black).

V


National Aeronautics and Space Administration Observation minus Forecast (RMS)Zonal Wind Jun-Aug 2014

U

0

1

2

3

4

5R

MS

(ms-1

)a

O minus FJun-Aug 2014

Blue: wo LoonRed: wi Loon

SHSH4.3e+6

EQEQ5.0e+5

NHNH1.8e+5

U

0

5

10

15

20

RM

S (m

s-1)

b|O-F| > 10 ms-1

SHSH7.9e+3

EQEQ1.1e+4

NHNH9.4e+1

V

0

1

2

3

4

5

RM

S (m

s-1)

c

SHSH4.3e+6

EQEQ5.0e+5

NHNH1.8e+5

V

0

5

10

15

20

RM

S (m

s-1)

d|O-F| > 10 ms-1

SHSH1.0e+4

EQEQ2.9e+3

NHNH1.7e+1

Latitude Bands Latitude BandsNumber of Observations

Con

trol

Loon

Con

trol

Loon

Con

trol

Loon

Con

trol

Loon

Con

trol

Loon

Con

trol

Loon

All Loon Observations Only times when Control and Loon Obsshow large (> 10m/s) differences

Assimilating the Loon winds greatly improves tropical wind forecast

TropicsTropics

1 m

/s

5m

/s



Summary and ConclusionsSummary: The Loon balloons were incorporated into a global data assimilation system for three months in order to test their impact. Date range: June-August 2014.Results: Assimilation of the Loon balloon winds had a significant impact in the tropical lower stratosphere, especially in regions were direct wind measurements are lacking.

Future Work: This preliminary study showed the potential for constant pressure balloon data to aid in real-time data assimilation system analyses and forecasts. We plan to assimilate the entire 3+ year Loon data set into the NASA GMAO data assimilation system for further tests.

References:Schoeberl, M. R., E. Jensen, A. Podglajen, L. Coy, C. Lodha, S. Candido, and R. Carver (2017), Gravity wave spectra in the lower stratosphere diagnosed from project loon balloon trajectories, J. Geophys. Res. Atmos., 122, 8517–8524, doi:10.1002/2017JD026471.

Podglajen, A., A. Hertzog, R. Plougonven, and B. Legras (2016), Lagrangian temperature and vertical velocity fluctuations due to gravity waves in the lower stratosphere, Geophys. Res. Lett., 43, 3543–3553, doi:10.1002/2016GL068148.

Friedrich, L. S., McDonald, A. J., Bodeker, G. E., Cooper, K. E., Lewis, J., and Paterson, A. J.: A comparison of Loon balloon observations and stratospheric reanalysis products, Atmos. Chem. Phys., 17, 855-866, https://doi.org/10.5194/acp-17-855-2017, 2017.

We would like to thank X and the Loon Project for providing their data.

Question: Is the current conventional and satellite observation network sufficient to characterize the winds in the lower stratosphere?

Answer: No

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