The use of HDO observations for The use of HDO observations for understanding processes controlling understanding processes controlling

the water vapor feedbackthe water vapor feedback

David NooneDept. Atmospheric and Oceanic Sciences and

Cooperative Institute for Research in Environmental SciencesUniversity of Colorado, Boulder CO

With Derek Brown (CU-Boulder), Joe Galewsky (UNM), John Worden (JPL), Kevin Bowman (JPL)

Objectives• Global observations of HDO and H2O in the mid/lower

troposphere • Use these to constrain water budget• Two observables gives more information than one

(isotopes tell about the processes)

Specifically• Why are subtropics dry? (How does this change?)• Identify sources of water

(Especially recycling of rainwater though re-evaporation)• Characterize type of cloud processes (in the tropics)• Characterize type of sink (remoistening in region of

convection, reversible adiabatic cloud processes, efficiency with which water is lost from the atmosphere)

Information from isotopes is on exchange processes

Reminder of isotope physics

1ocnR

R

Two simple isotope models…

Condensation

Vapor becomes depleted as heavy removed preferentially

HO

H

liquid (e.g., ocean)

vapor(e.g., atmosphere)

Evaporation

Returns to isotopic composition of the (ocean/land) source.

Ratio of HDO to H2O

Measured as a difference from ocean water.

Conditions under which condensation occurs is different from the conditions when evaporation occurs

HO

D

D climatology (850-500 hPa)

December 2004 – March 2008

Helliker and Noone in press, Noone, et al., in prep.

Averaging kernel diagonalDecember-January-February June-July-August

800-500 hPa layer has adequate sensitivity. (DOFs 0.5 – 1.2)

Unwise to look in upper troposphere/boundary layer

Tropics/subtropics most reliable

Dehydration

DehydrationDrying (mixing by eddies/weather)

Emmanuel and Pierhumbert, 1999

Isot

opic

dep

leti

on

Isotopes conserved

Debate in community – both impact climate change.

Isotopes differentiate the effects of “dynamics” versus “microphysics”

Isotopic

deplet

ion

Subtropical water source

What controls relative humidity?

D when RH is high minus D when RH is low(i.e., correlation, or slope” d(D)/d(RH)

Comparison with theoretical expectations (“hypotheses”) provides a measure of which processes control water vapor abundance

Noone, J Climate, in review

Processes: define box budgets

PEdt

dq

iii PE

dt

dq

Noone, J, Climate, in review

Ei/E given by Craig and Gordon (1965) (Fick’s law)

Pi/P assume fractionation against qi/q (Rayleigh-like)

Revers

ible m

oist

adiab

atic

)1(1

)1(ˆˆ1 Hq

HqR

R

s

00, ˆˆ qqqqH ii

00 ln1

q

q

ffe

e

)1(

Condensation Mixing/hydration

Pseu

doad

iabati

c

Very powerful analytic tool since constrains system

Two things to worry about:1) What is source composition? (end members, balance of sources)2) What is slope? (rainfall efficiency, type of cloud)

(Noone, in review)

Framework for interpreting HDO

PDFs of TES observations

W Pacific values where f>1, i.e., rain evaporation/exchange important

S./C. Pacific reversible adiabatic control (closed-system)

N. Pacific irreversible (Rayleigh)

Cloud/rainfall efficiency (JJA)

(Preliminary, adapted from Brown et al., in prep)

Measure of “how many times irreversible latent heating occurs”

i.e., The fraction of the water is removed from 850-500 hPa layer

Derived directly from knowing the isotopic fractionation ()

%

Land, ocean, sea ice

(-40/-80 ‰, or ~ -110 ‰)

Humidity, disequilibrium.

PBL

Precipitation,‰

Free troposphere‰

S‰

Liquid retained in subtropics

Schematic of findings: 40S-40N

Vapor recycled by rain evaporation

Polar troposphere‰ Isentropic mixing

Dry downdrafts

f < 1

f > 1 for convection

E

P

HAVAIKI 2008Hawaii atmospheric vapor isotope “k” intercomparison

Objectives1. Test laser spectrometers

JPL, Picarro, Los Gatos Research2. Provide validation opportunity for TES and IASI3. Science objectives

Understand hydrology of dry zones

PIs: David Noone (U. Colorado) and Joe Galewsky (U. New Mexico)

University of ColoradoPI: David NooneAdriana BaileyDerek BrownDarin Toohey

NASA JPLLance ChristensenChris WebsterJohn Worden

University of New MexicoPI: Joe GalewskyZach SharpJohn HurleyLeah JohnsonMel Strong

NOAA Mauna Loa ObsJohn Barnes

Los Gatos Research Feng DongDoug BaerManish Gupta

PicarroEric CrossonPriya GuptaAaron van Pelt

http://cires.colorado.edu/science/features/vapor/

LGR WVIA Picarro IWVA JPL TWI

Vacuum flasksCryogenic traps

Inlet

Noone et al., in prep,

TES Special Observations: Transects and Step & Stares

Continuation proposal being drafted: Synergy with ongoing TES and ongoing missions

ConclusionsTES HDO has allowed rethinking of atmospheric hydrology: more integrative (but tentative)

• Eddy transport processes at the edge of the subtropics important(moist air poleward, dry air equatorward)

• Captured the “cyclic” nature of the hydrologic cycle, not just state• Subtropics balance between:

– dehydration via mixing (although, not clear if this is from high latitude or high altitude)

– Moistening via (reversible) adiabatic processes– Rainfall evaporation/exchange important in convective regions

(within the subtropical mixing barrier)

Undergraduate textbooks are misleading: low humidity NOT caused by subsidence.

• Cloud processes quantified two opposing processes:1. remoistening “super-Rayleigh” in region of strong convection2. slow/reversible “sub-Rayleigh” in dry parts of the atmosphere

Fall just short of full partitioning due to lack of constraint (typically also use 18O, which we can not retrieve from TES)

Demonstrate relevance of precise long-term measurements of atmospheric water measurements in key regions (Mauna Loa, Darwin, Amazon, …) to assess the response to climate forcing and that these compliment ongoing remote sensing

Challenges and ongoing• Validation of TES HDO remains an issue

Lack of validation data (John Worden will speak to this)

Without this, one should be skeptical of science outcomes!

• Processes studies are limited by lack of vertical information (especially the boundary layer)

• Similarly, other science with upper troposphere sensitivity (18O must be on wish list for future missions)

• Modeling (GCMs) reached greater maturity (now ~10 models have isotopes). (Jeonghoon Lee/Kei Yoshimura)

• Real opportunities for TES HDO to constrain understanding of water cycle (Derek Brown/Kevin Bowman)