# Presentation: 562955

## A climatology of aircraft-borne in situ observations of relative humidity in clear air and clouds:An update from the AVE Missions

- A climatology of aircraft-borne *in situ *observations of relative humidity in clear air and clouds:An update from the AVE Missions

- Jessica B. Smith, J. Ryan Spackman, Jasna V. Pittman, Elliot M. Weinstock, James G. Anderson
*AURA Meeting *
*Tuesday, September 20, 2005*

## Relevance of Relative Humidity

-  	Clear air RHi measurements provide information about 	ice nucleation and cirrus formation
*Impacts the estimates of the frequency and **	**coverage of thin cirrus*
- 2)	In cloud RHi measurements provide an indication of the 	dehydration potential of cold near-tropopause cirrus
- 		* **Impacts the mixing ratio of water vapor entering **	**	**	**	**the stratosphere*

## Definition of Relative Humidity

- 	Relative Humidity with respect to ice (*RHi*) defined as:
- 		*RHi* = H2O/Saturation Mixing Ratio with respect to ice (*SMRi*)
- 	The accuracy of *RH**i* observations depends upon:
- Water Vapor
*SMRi(T)*
- [Murphy & Koop, QJRMS, 2005]
- 3) Temperature

## Missions		Water Vapor	Temperature

- _Missions_		_Water Vapor_	_Temperature_
- 		HWV	JLH	P/T	MMS
- CWVCS – Costa Rica, August 2001	 	 X	 	X
- Clouds and Water Vapor in the Climate System
- CRYSTAL-FACE – Key West, July 2002	 	 	 	
- Cirrus Regional Study of Tropical Anvils and Cirrus Layers –
- Florida Area Convection Experiment
- Pre-AVE – Costa Rica, January 2004	 	 	 	X
- Pre AURA Validation Experiment
- AVE-0506 – Houston, June 2005	 	 	 	 
- AURA Validation Experiment
- AVE-WIIF – Houston, July 2005	 	 	 	 
- Water vapor Isotope Inter-comparison Flights

## Missions	Water Vapor (Calibrated Accuracy)	

- _Missions_	_Water Vapor (Calibrated Accuracy)_
- 	HWV	(5%) 		JLH	 (5%)
- CRYSTAL-FACE	-	Agreed to within ~7% 5%
- 	-	JLH systematically high
- 	-	Clear Air: HWV
- 	- 	In Cloud: JLH* = JLH x 0.93 =
- 			JLHIC x (HWVCA / JLHCA)
- AVE-0506	-	H2O < 100 ppmv agreed to within ~5% 5%
- * AVE-WIIF *	-	Clear Air: HWV
- 	-	In Cloud: JLH
- 	-	*We have addressed this issue with a redesign of **	**	**HWV inlet*

## Missions	Temperature (Calibrated Accuracy)	

- _Missions_	_Temperature (Calibrated Accuracy)_
- 	MMS	(0.3 K) 	P/T	 (0.5 K)
*	**~3% in RHi**	**	**~5% in RHi*
- CRYSTAL-FACE	-	Agreed to within 0.25 K
- 	-	P/T colder
- 	-	MMS conservative choice
- AVE-0506	-	Differed by up to 1 K at the coldest temperatures
- * AVE-WIIF *	-	RHi uncertainty ~10 – 15%
- 	- 	P/T colder
*	**-**	**Issues being addressed, recalibrated*
*	*-	MMS chosen

## Clear Air RHi Observations:

- The Axes

## Clear Air RHi Observations:

- The Axes

## Clear Air RHi Observations:

- Laboratory Ice Nucleation Data

- Möhler, et al., ACP, 2003

## Clear Air RHi in situ Observations:

- CWVCS

## Clear Air RHi in situ Observations:

- CWVCS, C-F

## Clear Air RHi in situ Observations:

- CWVCS, C-F

**Consistent with **
**Laboratory Homogeneous **
**Nucleation Threshold**

**Exceeds Homogeneous **
**Nucleation Threshold**
**Chemistry?**

## Clear Air RHi in situ Observations:

- CWVCS, C-F, PreAVE

## Clear Air RHi in situ Observations:

- CWVCS, C-F, PreAVE, AVE-0506

## Clear Air RHi in situ Observations:

- CWVCS, C-F, PreAVE, AVE-0506, AVE-WIIF

## Clear Air RHi in situ Observations:

- 3 ppm, 80 mbar

- 5 ppm, 80 mbar

- CWVCS, C-F, PreAVE, AVE-0506, AVE-WIIF

## Clear Air RHi in situ Observations:

- CWVCS, C-F, PreAVE, AVE-0506, AVE-WIIF

**Consistent with **
**Laboratory Homogeneous **
**Nucleation Threshold**

**Exceeds Homogeneous **
**Nucleation Threshold**
**Chemistry?**

- Jensen, et al., ACP, 2004

## In Cloud RHi:

- The Axes

## In Cloud RHi in situ Observations:

- CWVCS

## In Cloud RHi in situ Observations:

- CWVCS, C-F

## In Cloud RHi in situ Observations:

- CWVCS, C-F

**Convergence Toward **
**100% RHi**

**Persistent High In-Cloud SS**
**Kinetics?**
**Chemistry?**

- RHi in High Surface Area Density Clouds:
- CRYSTAL-FACE

## In Cloud RHi in situ Observations:

- CWVCS, C-F

## In Cloud RHi in situ Observations:

- CWVCS, C-F, PreAVE

## In Cloud RHi in situ Observations:

- CWVCS, C-F, PreAVE, AVE-WIIF

## In Cloud RHi in situ Observations:

- CWVCS, C-F, PreAVE, AVE-WIIF

**Convergence Toward **
**100% RHi**

**Persistent High In-Cloud SS**
**Chemistry?**

## In Cloud RHi vs. Temp. & Ice Water Content:

- CWVCS, C-F, PreAVE, AVE-WIIF

**Persistent High In-Cloud SS**
**Observed Over a Wide Range **
**of Cloud Ice Water Content**

## RHi vs. Particle Surface Area Density & Temp.:

- AVE-WIIF

**Temperature (K)**

## RHi vs. Particle Surface Area Density & Temp.:

- AVE-WIIF

**Temperature (K)**

**In cloud DD****	****-545**
_**Clear air DD**__**	**__**-480**_
**	****lighter by ~60 ****‰**
**In cloud DD****	****-651**
_**Clear air DD**__**	**__**-530**_
**	****lighter by ~121****‰**

**In cloud DD****	****-482**
_**Clear air DD**__**	**__**-473**_
**  ****roughly equivalent**

## Conclusions

-  	T > 200 K - Highest clear air values consistent 	with the SS threshold for homogeneous 	nucleation threshold
-  	T < 200 K - Evidence for very high nucleation 	threshold in both Costa Rica data sets – values 	approaching water saturation
- Observation of persistent in-cloud supersaturation
-  	T < 200 K - Apparent equilibrium supersaturation 	~120%
-  	Insensitivity to particle surface area density
- Importance of redundant measurements!

## Acknowledgements

-  	Paul Bui (MMS)
-  	Tommy Thompson (P/T)
-  	Harvard ICOS & HOx Teams
-  	Eric Jensen
-  	Pilots and Crew of WB57

## Slide 32

## Slide 33

## Slide 34

## Crystal-Face - 20020723