Tropopause Folds: Results from NOAA Unmanned Aircraft Systems (UAS) Demo and Network Observations

J.W. Elkins1, D. F. Hurst1,2, F.L. Moore1,2, S. J. Oltmans1,

G.S. Dutton1,2, J. D. Nance1,2, B. A. Vasel1,2, B. Johnson1,

P.M. Lang1, and S. A. Montzka1

1NOAA/ESRL/GMD and 2CIRES

What is a tropopause fold?• Folds are stratospheric intrusion of air that

sinks beneath the upper tropospheric jet stream.

• Folds formed by a steepening of the tropopause at a jet core. Occurrences are common with major fronts and movement of polar stratospheric air into the midlatitudes.

• Folds are the dominant and most efficient form of short-term (days-weeks) Stratosphere-Troposphere Exchange (STE)

• Brewer-Dobson Circulation makes up the long-term (years), large scale STE of air from the upper tropical troposphere to polar stratosphere.

Brewer-Dobson Circulation

Fold

Why are tropopause folds important?

• Transport (STE) is important because most sources gases are destroyed in the stratosphere, however ozone is produced there.

• Folds may play a role in the seasonal distribution of long lived source gases, N2O and CFCs by mixing lower stratospheric mixing ratios with tropospheric levels (Nevison et al., 2004; Liao et al., 2004).

• Folds may be key to removal of stratospheric sulfate aerosols by deposition into the troposphere.

• Clean, dry stratospheric air, rich in ozone and potential vorticity (PV) is transported downward to the troposphere.

• Tropospheric air (large amount of water, CO, aerosols, and low PV) also is advected upwards as well.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

A well-pronounced tropopause fold is forecast to occupy the mid- and upper troposphere above Friday's (Feb 5, ‘99) flight track. The following forecast is for 1800 UTC, Feb. 5. Figure shows the forecast 2 PV (tropopause)isosurface for 1800 UTC Friday, Feb. 5. Potential temperature on this surface is indicated with shading. The tip of the fold penetrates beneath the 5 km level. Orange streamlines are shown at 3 km (10,000 ft) above sea level, for reference. (Univ. of Virginia, INTEX NA (Atlantic)Web page)

NOAA/ESRL UAS Chromatograph for Atmospheric Trace Species (UCATS)

1. Box weighs 22 kg (48 lbs.), 24.6 x 40.6 x 45.7 cm (9.7x16x18.1”), 45.6 liters2. Measures O3 once every 10 seconds (commercial unit 2B,Inc.)3. Measures N2O, SF6, CFC-11, CFC-12, halon-1211 once every 70 seconds. On board calibration.1. In the future, could measure( PAN, PPN) or (CO, H2, CH4) for tropospheric mission.

Compounds in red are measured by Aura Satellite Instruments.

Maps of 19 April 2005 Event

PV plot courtesy ofLeslie Lait, (NASA/GSFC)

Observation of Tropopause Fold on the UAS Altair

A

B

Five hour test flight finds fold aboveGray Butte, CA airfield.

PV plot courtesy ofLeslie Lait, (NASA/GSFC)

A

B

THD

A tropopause fold.

From Michael Ives internalMeeting talk on Monday.

What is the cause of multiple peaks in ozonesondes at Trinidad, Head, CA (THD)?

PV cross sectional plot courtesy of Eric Ray, ESRL/CSDPurple=polar air

What is the frequency of folds at Trinidad Head?

• Established 3 necessary criteria for determining the presence of a fold.

• (1) Tropopause height lowered from 15 km.

• (2) Ozone (O3) slope changes of 50 ppb (100m level).

• (3) Small peaks of O3

observed in troposphere (<10 km)

• Used all sondes from 21 Aug 1997 to 3 Mar 2006.

Typical sonde-no fold.

Possible tropopause fold event

Results from Trinidad Head (THD)

• 481 flights with 13 failed launches, 10 flights with no data to tropopause (not used).

• 47 out of 458 flights identified with possible folds (10.3%).

• Late winter and spring have the highest monthly frequency (right).

• Compares with previous ozonesonde study (Van Haver et al., 1996, GRL) of 2-5% of the total sondes have folds. A climatological study (Elbern et al., 1998) calculates an average of 11,000 fold days per year .

Conclusions and further work.• Folds last for days. Altair UAS is good platform

for studying folds because of long endurance (20+ hours) and low speed (120 kts).

• Ozonesonde records with PV analysis confirm the presence of folds.

• Frequency of folds probably varies geographically, need to look at other ozonesonde records.

• Need to develop techniques to calculate the net flux into the troposphere.

• Addition of a water instrument (TDL, top right) to UCATS instrument will help since folds bring down low RH air.

• More Altair UAS missions this summer (NASA Fire) and next year (NASA Aura). Addition of the UAS Global Hawk (bottom right) to atmospheric research is a plus with more payload.

Randy May’s H2O TDL

Global Hawk UAS