# Presentation: 306751

## TES Observations of HDO and H2O 1John Worden, 1Kevin Bowman, 2David NooneTES team members, and 1Christopher Webster 

*1**JPL / Caltech*
*2**CIRES / U. of Colorado*

## Background on Water Isotopes

- Reference for water isotopes is the Standard Mean Ocean Water (SMOW) = 3.1 x 10-4 HDO/H2O

- Water isotopes are a good tracer for the origin, condensation, and evaporation history of an air parcel
- Lighter isotopes preferentially evaporate
- Heavier isotopes preferentially condense  (More condensation leads to more depletion)
- Isotopic composition of water vapor over the ocean is a well known function of temperature.

- D of tropospheric water vapor varies from approximately -79 (above ocean) to -800 in upper troposphere.

- 10% depleted = -100‰
- 100% depleted = -1000‰

## Previous Measurements of Water Isotopes

- However these precipitation measurements  do not necessarily reflect cloud processes because of the tendency of rain-drops to equilibrate to the isotopic composition of the background vapor as the raindrops fall and therefore losing the isotopic signature of the cloud! (Friedman et al., JGR, 1962)
- Useful to measure the isotopic composition of both vapor and condensate!
- Very few observations of the isotopic composition of water vapor exist!
- Balloon (FIRS),  satellite (ATMOS, ACE ) and in situ measurements (ALIAS  and Harvard) of isotopic composition of water vapor are used to better understand processes and sources controlling humidity in the upper troposphere and lower stratosphere
- Boundary layer observations of HDO, H218O, H2O (e.g., Lawrence et al., 2004) used to characterize dynamics, precipitation, and evaporation processes of tropical storms

## Retrieval Approach

_**Retrieval Approach**_
- Simultaneous retrieval of HDO and H2O reduces systematic errors of the estimated HDO/H2O ratio  (*Worden et al., JGR, submitted*)
- Keep *a priori* and initial guess for the HDO/H2O ratio fixed over whole globe so as to better examine spatial variability

## Greatest sensitivity to tropospheric HDO/H2O ratio at 750 hPa

- Greatest sensitivity to tropospheric HDO/H2O ratio at 750 hPa

## Random error increases as surface temperature (or signal-to-noise) decreases

- Random error sufficient to capture regional and global variations of HDO/H2O ratio

- Sensitivity of retrieval to the tropospheric HDO/H2O ratio decreases with surface temperature (or signal-to-noise)

## “Latitude effect” We observe more depletion with increasing latitude due to gradual rainout of heavier isotopes as air moves pole-ward

- “Continent Effect”
- Precipitation Measurement ==> More depleted over continents relative to ocean
- TES Vapor Measurements ==> No obvious continent effect
- Evapo-Transpiration source larger than expected?

## TES and WB-57 ALIAS observations show similar distributions that lie within condensation and evaporation end-member models 

- TES and WB-57 ALIAS observations show similar distributions that lie within condensation and evaporation end-member models

## Global Distribution of tropospheric water vapor is well described by combination of evaporation from ocean and condensation

- Observations below condensation models and above evaporation models require additional water source terms or processes to explain and will be discussed at the AGU

## Summary

- TES retrievals of HDO/H2O ratio are most sensitive to air-mass at 750 hPa.
- Random errors of retrievals range from 10 ‰ to 25 ‰ which is sufficient for capturing regional and global variations
- TES retrievals have been compared to WB-57 ALIAS in situ measurements and the observed distributions are consistent

- Results
-   We observe the “latitude effect” which is due to gradual rain-out of heavier isotopes
-   We do not observe significantly depleted vapor over the continents in contrast to precipitation measurements
-   Global distribution of tropospheric water vapor well described by evaporation and condensation
-   More science to come and shown at the AGU!