Troposphere to stratosphere transport at low latitudes as studies using HALOE observations of water vapour 1992–1997

In this paper we present observations of water vapour (version 18 retrievals) in the equatorial tropopause region made by the Halogen Occulatation Experiment (HALOE) instrument, which files on the Upper Atmosphere Research Satellite. These data make an important new contribution to the observationl knowledge of this region, since water vapour here has largely been observed to date using in situ instruments, and the only global longitudinally‐resolving satellite observations to be reported are those from the Stratospheric Aerosol and Gas Experiment II (SAGE II). Firstly, the HALOE water vapour climatology is presented. Comparison of HALOE and SAGE II climatologies shows considerable agreement. An exception is over Asia in June, July and August (JJA), where the HALOE fields show a distinct region of moist air (associated with convection due to the Asian summer monsoon), whereas no such feature was reported in the SAGE II observations. This suggests that HALOE is sensitive to water vapour variability near the tropopause over regions of strong convection. Secondly, the troposphere to stratosphere transport of air at low latitudes is investigated. Pressure/longitude sections near the equator show that dry air with water vapour mixing ratios of less than 2.4 parts per million by volume (p.p.m.v.) enters the stratosphere in December, January and February, then travels upwards and polewards in the subsequent seasons. A more detailed examination of pressure/longitude sections indicates episodes when dry air also enters the equatorial stratosphere in March, April and May and JJA at times of strong convenction. There is also evidence of entry of air with higher water vapour mixing ratios, of between 3.6 and 4.0 p.p.m.v, into the stratosphere in September, October and November, chiefly at 10°N and 20°N. Further examination of the region of moist air over Asia in JJA (mentioned above) shows that there is clear cross‐isentropic upward transport in the 375–410 K region of unsaturated air. The HALOE water vapour data set reported here provides an important new insight into low latitude processes near the equatorial tropopause.

[1]  L. Froidevaux,et al.  Validation of UARS microwave limb sounder 183 GHz , 1996 .

[2]  Wesley A. Traub,et al.  Validation of measurements of water vapor from the Halogen Occultation Experiment (HALOE) , 1996 .

[3]  P. Mote,et al.  An atmospheric tape recorder: The imprint of tropical tropopause temperatures on stratospheric water vapor , 1996 .

[4]  J. Russell,et al.  On the distribution of mesospheric molecular hydrogen inferred from HALOE measurements of H2O and CH4 , 1996 .

[5]  Richard B. Rood,et al.  Upper-tropospheric water vapor from UARS MLS , 1995 .

[6]  P. Mote,et al.  Seasonal Variations of Water Vapor in the Tropical Lower Stratosphere , 1995 .

[7]  Brian E. Potter,et al.  The Role of Monsoon Convection in the Dehydration of the Lower Tropical Stratosphere , 1995 .

[8]  S. Oltmans,et al.  Increase in lower-stratospheric water vapour at a mid-latitude Northern Hemisphere site from 1981 to 1994 , 1995, Nature.

[9]  James M. Russell,et al.  Aerosol effects and corrections in the Halogen Occultation Experiment , 1995 .

[10]  Richard Swinbank,et al.  A Stratosphere-Troposphere Data Assimilation System , 1994 .

[11]  James M. Russell,et al.  The Halogen Occultation Experiment , 1993 .

[12]  K. Kelly,et al.  Water vapor and cloud water measurements over Darwin during the STEP 1987 tropical mission , 1993 .

[13]  David Rind,et al.  Overview of the Stratospheric Aerosol and Gas Experiment II water vapor observations - Method, validation, and data characteristics , 1993 .

[14]  D. Rind,et al.  Annual variations of water vapor in the stratosphere and upper troposphere observed by the Stratospheric Aerosol and Gas Experiment II , 1993 .

[15]  J. Ovarlez.  Stratospheric water vapor measurement in the tropical zone by means of a frost point hygrometer on board long‐duration balloons , 1991 .

[16]  D. Fahey,et al.  Observations of denitrification and dehydration in the winter polar stratospheres , 1990, Nature.

[17]  L. Heidt,et al.  A comparison of ER-2 measurements of stratospheric water vapor between the 1987 Antarctic and 1989 Arctic Airborne missions , 1990 .

[18]  A. J. Miller,et al.  A comparison of Arctic lower stratospheric winter temperatures for 1988–89 with temperatures since 1964 , 1990 .

[19]  J. Pyle,et al.  The water vapour budget of the stratosphere studied using LIMS and SAMS satellite data , 1986 .

[20]  S. Oltmans,et al.  Stratospheric water vapor variability for Washington, DC/Boulder, CO - 1964-82 , 1983 .

[21]  E. Danielsen.  A dehydration mechanism for the stratosphere , 1982 .

[22]  T. L. Thompson,et al.  Transport of water through the tropical tropopause , 1982 .

[23]  R. Newell,et al.  A Stratospheric Fountain , 1981 .

[24]  T. L. Thompson,et al.  In Situ Measurements of the Mixing Ratio of Water Vapor in the Stratosphere , 1979 .

[25]  J. Harries.  The distribution of water vapor in the stratosphere , 1976 .

[26]  H. J. Mastenbrook.  Water-vapor Measurements in the Lower Stratosphere , 1974 .

[27]  G. Dobson.  Origin and distribution of the polyatomic molecules in the atmosphere , 1956, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[28]  A. W. Brewer.  Evidence for a world circulation provided by the measurements of helium and water vapour distribution in the stratosphere , 1949 .

[29]  M. McCormick,et al.  Proposed reference model for middle atmosphere water vapor , 1996 .