NDBC TAO: Climatology Information

NDBC TAO: Climatology Information

The various Climatologies used by the TAO process to compute anomalies are briefly described below.

Reynolds and Smith AOI SST Climatology (1971 - 2000)

The AOI SST climatology is an optimum interpolation analysis of Sea Surface Temperature with an adjusted base period of 1971 to 2000, on a global 1 degree by 1 degree by 1 month grid. We began using this version of the Reynolds and Smith climatology July 23, 2002. The previous climatology had a base period of 1961-1990.

For further information, please see:

Smith, T. M. and R. W. Reynolds, 1998: A high resolution global sea surface temperature climatology for the 1961-90 base period. J. Climate, 11, 3320-3323.

Xue, Y., T.M. Smith and R.W. Reynolds, 2002: A new SST climatology for the 1971-2000 base period and interdecadal changes of 30-year SST normals. J. Climate in revision.

Subsurface Temperature Climatology

The Kessler temperature climatology is a 4-D objective analysis of historical XBT and CTD temperatures, which uses estimates of the correlation lengths in longitude, latitude, and time to grid the data. The data used in the analysis consist of all available CTD observations from the 1960s through 1991, plus earlier hydrocast station data. The XBT data range in time from 1970 to 1987. Basic data sets and procedures are described in Kessler (1990) and Kessler and McCreary (1993).

After merging XBT and CTD data, we further smoothed the climatologies to eliminate unrealistic features related to uneven data distribution in space and time. We then blended this climatology with the Reynolds and Smith SST climatology to ensure consistency between surface anomalies appearing in vertical and horizontal temperature analyses. Blending was done such that surface values were set to Reynolds and Smith and values between 0 and 50 m generated by linear interpolation between SST and Kessler values at 50 m. Any discontinuities across 50 m were smoothed out and any near surface temperature instabilities generated by this blending were eliminated. As a final step, monthly values were smoothed with a 1-2-1 filter in time to eliminate small amplitude month-to-month noise variations.

This climatology is used for gridding the TAO subsurface temperatures in Longitude-Depth and Latitude-Depth sections. A special exception to this is along 95°W for Latitude-Depth sections. Since we have data at 12°N during the EPIC program, which are located outside the domain of the modified Kessler climatology (extending only to 10°N), we use instead the Bureau of Meteorology Research Center (BMRC) temperature climatology (Smith, 1995) at all latitudes along 95°W so that the anomalies in the 95°W depth-section plots are coherent and extend to 12°N. This introduces a small inconsistency between anomalies shown in the Depth-Longitude and Latitude-Depth section plots at 95°W.

For additional information see:

Kessler, W.S., 1990: "Observations of long Rossby waves in the northern tropical Pacific". J. Geophysical Research, 95(C4), 5183-5217 (abstract) ,

Kessler, W.S. and J.P. McCreary, 1993: "The annual wind-driven Rossby wave in the subthermocline equatorial Pacific". J. Phys. Oceanogr., 23(6), 1192-1207 (abstract)

Smith, N. R., 1995: "An improved system for tropical ocean sub-surface temperature analyses". J. Atmos. Oceanic Technol., 12, 850-870.

COADS Winds (1946 - 1989)

The COADS climatologies of Zonal and Meridional Wind, Scalar Wind Speed, and Wind Direction are used for computing TAO Wind anomalies and for gridding Zonal and Meridional Winds and Scalar Wind Speed in the Latitude-Time section plots.

World Ocean Atlas Temperature Climatology

The World Ocean Atlas (See Conkright et al. 2002: "World Ocean Atlas 2001: Objective Analyses, Data Statistics, and Figures, CD Rom Documentation", US Dept. of Commerce) temperature climatology is used to compute temperature anomalies at locations other than the tropical Pacific.

COADS Relative Humidity (1946 - 1989)

The Relative Humidity (RH) climatology was derived from the COADS Specific Humidity (SH) climatology. The SH climatology was converted to RH using a routine written by Ms. Margie McCarty at NOAA/PMEL, which takes as input SH, pressure, and air temperature.

This climatology is used for computing TAO RH anomalies and for gridding RH in the Latitude-Longitude Maps and Latitude-Time section plots.

COADS Sea Level Barometric Pressure (1946 - 1989)

The Sea Level Pressure (SLP) climatology is used for computing TAO SLP anomalies and for gridding SLP in the Latitude-Time section plots.

20°C Isotherm Depth

The 20°C Isotherm Depth climatology was computed from the Kessler temperature climatology (see above), by linear interpolation of depth versus temperature.

This climatology is used for computing TAO 20 degree C Isotherm depth anomalies and for gridding 20°C depths in the Latitude-Longitude Maps and Latitude-Time section plots.

Dynamic Height

The Dynamic Height climatology was computed from the Kessler temperature climatology (see above), by vertically integrating the specific volume anomaly using a set of long-term mean temperature-salinity relations, one for each grid location, derived from the "World Ocean Atlas 2001" (See Conkright et al 2002: "World Ocean Atlas 2001: Objective Analyses, Data Statistics, and Figures, CD Rom Documentation", US Dept. of Commerce)

This climatology is used to compute Dynamic Height anomalies and for gridding Dynamic Heights in the Latitude-Longitude Maps and Latitude-Time section plots.

Salinity and Sigma-Theta

The World Ocean Atlas climatologies (See Conkright et al. 2002: "World Ocean Atlas 2001: Objective Analyses, Data Statistics, and Figures, CD Rom Documentation", US Dept. of Commerce) include salinity and temperature. The salinity climatology is used to compute salinity anomalies. The salinity and temperature climatologies are used to compute a climatology of sigma-theta, which is used to compute sigma-theta anomalies. Sigma-theta is computed as follows:

Salinity is combined with potential temperature computed from the World Ocean Atlas temperature climatology to compute the potential density anomaly (sigma-theta) defined as sigma-theta = 1/V(S,Theta,P) -1000 kg m-3 where V is specific volume, S is salinity, Theta is potential temperature and P is set to zero. The algorithms used in these calculations are from "Algorithms for computation of fundamental properties of seawater" by Fofonoff and Millard (UNESCO technical papers in marine science, 44, 1983).

Shortwave Radiation (1945-1989)

The shortwave solar radiation climatology from the "ATLAS of Surface Marine Data" (da Silva et al., 1994) is used to compute anomalies.

Longwave Radiation (1945-1989)

The outgoing longwave radiation climatology from the "ATLAS of Surface Marine Data" (da Silva et al., 1994) is used to compute anomalies.

Xie and Arkin Precipitation Climatology (1979 - 1995)

The precipitation climatology from Xie and Arkin (1997) is used to compute anomalies.

Sea Surface Ocean Currents

The surface current climatology from Reverdin et al. (1994) is used to compute anomalies.