Upper-tropospheric relative humidity observations and implications for cirrus ice nucleation

Andrew J. Heymsfield; Larry M. Miloshevich; Cynthia Twohy; Glen Sachse; Samuel Oltmans

doi:10.1029/98GL01089

Upper-tropospheric relative humidity observations and implications for cirrus ice nucleation

Andrew J. Heymsfield, Larry M. Miloshevich, Cynthia Twohy, Glen Sachse, Samuel Oltmans

Dynamical and Physical Meteorology

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105 Scopus citations

Abstract

Relative humidity (RH) measurements acquired in orographic wave cloud and cirrus environments are used to investigate the temperature-dependent RH required to nucleate ice crystals in the upper troposphere, RH_nuc(T). High ice-supersaturations in clear air - conducive to the maintenance of aircraft contrails yet below RH_nuc and therefore insufficient for cirrus formation - are not uncommon. Earlier findings are supported that RH_nuc in mid-latitude, continental environments decreases from water-saturation at temperatures above -39 °C to 75% RH at -55 °C. Uncertainty in determining RH_nuc below -55 °C results in part from size detection limitations of the microphysical instrumentation, but analysis of data from the SUCCESS experiment indicates that RH_nuc below -55 °C is between 70 and 88%. A small amount of data acquired off-shore suggests the possibility that RH_nuc may also depend on properties of the aerosols.

Original language	English
Pages (from-to)	1343-1346
Number of pages	4
Journal	Geophysical Research Letters
Volume	25
Issue number	9
DOIs	https://doi.org/10.1029/98GL01089
State	Published - May 1 1998

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title = "Upper-tropospheric relative humidity observations and implications for cirrus ice nucleation",

abstract = "Relative humidity (RH) measurements acquired in orographic wave cloud and cirrus environments are used to investigate the temperature-dependent RH required to nucleate ice crystals in the upper troposphere, RHnuc(T). High ice-supersaturations in clear air - conducive to the maintenance of aircraft contrails yet below RHnuc and therefore insufficient for cirrus formation - are not uncommon. Earlier findings are supported that RHnuc in mid-latitude, continental environments decreases from water-saturation at temperatures above -39 °C to 75\% RH at -55 °C. Uncertainty in determining RHnuc below -55 °C results in part from size detection limitations of the microphysical instrumentation, but analysis of data from the SUCCESS experiment indicates that RHnuc below -55 °C is between 70 and 88\%. A small amount of data acquired off-shore suggests the possibility that RHnuc may also depend on properties of the aerosols.",

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T1 - Upper-tropospheric relative humidity observations and implications for cirrus ice nucleation

AU - Heymsfield, Andrew J.

AU - Miloshevich, Larry M.

AU - Twohy, Cynthia

AU - Sachse, Glen

AU - Oltmans, Samuel

PY - 1998/5/1

Y1 - 1998/5/1

N2 - Relative humidity (RH) measurements acquired in orographic wave cloud and cirrus environments are used to investigate the temperature-dependent RH required to nucleate ice crystals in the upper troposphere, RHnuc(T). High ice-supersaturations in clear air - conducive to the maintenance of aircraft contrails yet below RHnuc and therefore insufficient for cirrus formation - are not uncommon. Earlier findings are supported that RHnuc in mid-latitude, continental environments decreases from water-saturation at temperatures above -39 °C to 75% RH at -55 °C. Uncertainty in determining RHnuc below -55 °C results in part from size detection limitations of the microphysical instrumentation, but analysis of data from the SUCCESS experiment indicates that RHnuc below -55 °C is between 70 and 88%. A small amount of data acquired off-shore suggests the possibility that RHnuc may also depend on properties of the aerosols.

AB - Relative humidity (RH) measurements acquired in orographic wave cloud and cirrus environments are used to investigate the temperature-dependent RH required to nucleate ice crystals in the upper troposphere, RHnuc(T). High ice-supersaturations in clear air - conducive to the maintenance of aircraft contrails yet below RHnuc and therefore insufficient for cirrus formation - are not uncommon. Earlier findings are supported that RHnuc in mid-latitude, continental environments decreases from water-saturation at temperatures above -39 °C to 75% RH at -55 °C. Uncertainty in determining RHnuc below -55 °C results in part from size detection limitations of the microphysical instrumentation, but analysis of data from the SUCCESS experiment indicates that RHnuc below -55 °C is between 70 and 88%. A small amount of data acquired off-shore suggests the possibility that RHnuc may also depend on properties of the aerosols.

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U2 - 10.1029/98GL01089

DO - 10.1029/98GL01089

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EP - 1346

JO - Geophysical Research Letters

JF - Geophysical Research Letters

IS - 9

ER -

Upper-tropospheric relative humidity observations and implications for cirrus ice nucleation

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