Performance of the ECMWF Operational Analyses over the Tropical Indian Ocean

Badrinath Nagarajan Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, Canada

Search for other papers by Badrinath Nagarajan in
Current site
Google Scholar
PubMed
Close
and
Anantha R. Aiyyer Department of Earth and Atmospheric Sciences, The University at Albany, State University of New York, Albany, New York

Search for other papers by Anantha R. Aiyyer in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The quality of the ECMWF operational analyses is evaluated against independent upper-air sounding data collected during the Joint Air–Sea Monsoon Interaction Experiment (JASMINE; April–May 1999) and the Indian Ocean Experiment (INDOEX; February–March 1999).

Statistics of the difference between observations and analyses are compiled for temperature, humidity, and wind speed. The results show that the analyzed temperature has a cold bias between 1000 and 750 hPa. However, in the upper troposphere, a warm bias occurs between 350 and 150 hPa, while a cold bias is seen above 150 hPa. Compared to the observations, the analyzed humidity is lower between 1000 and 950 hPa and higher between 950 and 750 hPa. The analyzed wind speeds are close to observations over much of the troposphere, except near the tropopause, where they are overestimated by 1–2 m s−1 in the analyses. The low-level (1000– 750 hPa) biases in moisture and temperature in the ECMWF analyses over the Indian Ocean are similar to those reported for the tropical Pacific Ocean in past studies.

The occurrence of a cold and dry bias in the lowest 50 hPa indicates reduced convective available potential energy, which will render difficult the initiation and development of convection in numerical models initialized with these analyses. The moisture biases arise most likely because of the poor fit to humidity observations by the four-dimensional variational data assimilation scheme. This suggests that a better fit to humidity observations will yield an improved water vapor climatology over the Arabian Sea and Indian Ocean.

Corresponding author address: Anantha Aiyyer, Es 333, Dept. of Earth and Atmospheric Sciences, The University at Albany, State University of New York, 1400 Washington Ave., Albany, NY 12222. Email: aiyyer@atmos.albany.edu

Abstract

The quality of the ECMWF operational analyses is evaluated against independent upper-air sounding data collected during the Joint Air–Sea Monsoon Interaction Experiment (JASMINE; April–May 1999) and the Indian Ocean Experiment (INDOEX; February–March 1999).

Statistics of the difference between observations and analyses are compiled for temperature, humidity, and wind speed. The results show that the analyzed temperature has a cold bias between 1000 and 750 hPa. However, in the upper troposphere, a warm bias occurs between 350 and 150 hPa, while a cold bias is seen above 150 hPa. Compared to the observations, the analyzed humidity is lower between 1000 and 950 hPa and higher between 950 and 750 hPa. The analyzed wind speeds are close to observations over much of the troposphere, except near the tropopause, where they are overestimated by 1–2 m s−1 in the analyses. The low-level (1000– 750 hPa) biases in moisture and temperature in the ECMWF analyses over the Indian Ocean are similar to those reported for the tropical Pacific Ocean in past studies.

The occurrence of a cold and dry bias in the lowest 50 hPa indicates reduced convective available potential energy, which will render difficult the initiation and development of convection in numerical models initialized with these analyses. The moisture biases arise most likely because of the poor fit to humidity observations by the four-dimensional variational data assimilation scheme. This suggests that a better fit to humidity observations will yield an improved water vapor climatology over the Arabian Sea and Indian Ocean.

Corresponding author address: Anantha Aiyyer, Es 333, Dept. of Earth and Atmospheric Sciences, The University at Albany, State University of New York, 1400 Washington Ave., Albany, NY 12222. Email: aiyyer@atmos.albany.edu

Save
  • Andersson, E., and H. Jarvinen, 1999: Variational quality control. Quart. J. Roy. Meteor. Soc, 125 , 697722.

  • Courtier, P., and Coauthors, 1998: The ECMWF implementation of the three-dimensional variational assimilation (3D-VAR). I: Formulation. Quart. J. Roy. Meteor. Soc, 124 , 17831807.

    • Search Google Scholar
    • Export Citation
  • ECMWF, 1999: The description of the evolution of the ECMWF forecasting system and corresponding archive. ECMWF, Reading, United Kingdom. 126 pp.

    • Search Google Scholar
    • Export Citation
  • Grabowski, W. W., X. Wu, and M. W. Moncrieff, 1996: Cloud-resolving modeling of tropical cloud systems during Phase III of GATE. Part I: Two dimensional experiments. J. Atmos. Sci, 53 , 36843709.

    • Search Google Scholar
    • Export Citation
  • Gregory, D., J-J. Morcrette, C. Jakob, C. M. Beljaars, and T. Stockdale, 2000: Revision of convection, radiation and cloud schemes in the ECMWF Integrated Forecasting System. Quart. J. Roy. Meteor. Soc, 126 , 16851710.

    • Search Google Scholar
    • Export Citation
  • Guichard, F., D. Parsons, and E. Miller, 2000: Thermodynamic and radiative impact of the correction of sounding humidity bias in the Tropics. J. Climate, 13 , 36113624.

    • Search Google Scholar
    • Export Citation
  • Klinker, E., F. Rabier, G. Kelly, and J-F. Mahfouf, 2000: The ECMWF operational implementation of four-dimensional variational assimilation. III: Experimental results and diagnostics with operational configuration. Quart. J. Roy. Meteor. Soc, 126 , 11901215.

    • Search Google Scholar
    • Export Citation
  • Krishnamurti, T. N., B. Jha, P. J. Rasch, and V. Ramanathan, 1997: A high resolution global reanalysis highlighting the winter monsoon. Meteor. Atmos. Phys, 64 , 123150.

    • Search Google Scholar
    • Export Citation
  • Lin, X., and R. H. Johnson, 1996: Kinematic and thermodynamic characteristics of the flow over the western Pacific warm pool during TOGA COARE. J. Atmos. Sci, 53 , 695715.

    • Search Google Scholar
    • Export Citation
  • Loehrer, S. M., T. A. Edmands, and J. A. Moore, 1996: TOGA COARE upper-air sounding data archive: Development and quality control procedures. Bull. Amer. Meteor. Soc, 77 , 26512671.

    • Search Google Scholar
    • Export Citation
  • Lucas, C., and E. J. Zipser, 2000: Environmental variability during TOGA COARE. J. Atmos. Sci, 57 , 23332350.

  • Mahfouf, J-F., and F. Rabier, 2000: The ECMWF operational implementation of four-dimensional variational assimilation. II: Experimental results with improved physics. Quart. J. Roy. Meteor. Soc, 126 , 11711190.

    • Search Google Scholar
    • Export Citation
  • Nagarajan, B., M. K. Yau, and D-L. Zhang, 2001: A numerical study of a mesoscale convective system during TOGA COARE. Part I: Model description and verification. Mon. Wea. Rev, 129 , 25012520.

    • Search Google Scholar
    • Export Citation
  • Nuret, M., and M. Chong, 1996: Monitoring the performance of the ECMWF operational analysis using the enhanced TOGA COARE observational network. Wea. Forecasting, 11 , 5365.

    • Search Google Scholar
    • Export Citation
  • Rabier, F., H. Jarvinen, E. Klinker, J-F. Mahfouf, and A. Simmons, 2000: The ECMWF operational implementation of four-dimensional variational assimilation. I: Experimental results with simplified physics. Quart. J. Roy. Meteor. Soc, 126 , 11431170.

    • Search Google Scholar
    • Export Citation
  • Ramanathan, V., and Coauthors, 2001: Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze. J. Geophys. Res, 106 (D22) 2837128381.

    • Search Google Scholar
    • Export Citation
  • Stensrud, D. J., and J-W. Bao, 1992: Behaviors of variational and nudging assimilation techniques with a chaotic low-order model. Mon. Wea. Rev, 120 , 30163028.

    • Search Google Scholar
    • Export Citation
  • Su, H., S. S. Chen, and C. S. Bretherton, 1999: Three-dimensional week-long simulations of TOGA COARE convective systems using the MM5 mesoscale model. J. Atmos. Sci, 56 , 23262344.

    • Search Google Scholar
    • Export Citation
  • Tiedtke, M., 1993: Representation of clouds in large-scale models. Mon. Wea. Rev, 121 , 30403061.

  • Vesperini, M., 1998: Humidity in the ECMWF model: Monitoring of operational analyses and forecasts using SSM/I observations. Quart. J. Roy. Meteor. Soc, 124 , 13131327.

    • Search Google Scholar
    • Export Citation
  • Webster, P. J., and R. Lukas, 1992: TOGA COARE: The Coupled Ocean Atmosphere Response Experiment. Bull. Amer. Meteor. Soc, 73 , 13771416.

    • Search Google Scholar
    • Export Citation
  • Webster, P. J., and Coauthors, 2002: The JASMINE pilot study. Bull. Amer. Meteor. Soc, 83 , 30403061.

  • Zhang, D-L., and J. M. Fritsch, 1986: Numerical simulation of the meso-β-scale structure and evolution of the 1977 Johnstown flood. Part I: Model description and verification. J. Atmos. Sci, 43 , 19131943.

    • Search Google Scholar
    • Export Citation
  • Zipser, E. J., and R. H. Johnson, 1998: Systematic errors in radiosonde humidities: A global problem? Preprints, 10th Symp. on Meteorological Observations and Instrumentation. Phoenix, AZ, Amer. Meteor. Soc., 72–73.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 133 44 5
PDF Downloads 80 30 4