EPIC ITCZ Integrated Dataset

Download the Dataset
epic_itcz_meanomega_prprec.nc

Other EPIC websites
EPIC Data at NCAR EOL
EPIC Data at NOAA ESRL
EPIC Data at Colorado State
EPIC Sc Integrated Dataset

Examine Bibliography
References

Examine the Fields
lat, lon, tsec, nbdate, phis, Ps, Ptend, Tg, shflx, lhflx, Ts, qs, Tskin, u, v, omega, T, q, divT, divq, divq_raw, prec_ship, areaprec_pr, prec_gt, prec_pr, prec_rt, prec_c1, cldisccp, toaswdn, toaswup, toalwup, srfswdn, srflwdn, srfswup, srflwup, toaswupc, toalwupc, srfswdnc, srflwdnc, srfswupc, srflwupc, cloudcr, wdoppcr, Zcrbins, Zprbins, isccpbins, udopp, vdopp, divg, std_divg

Contact Us by Email
pblossey at u dot washington dot edu


The East Pacific Investigation of Climate in the Coupled Ocean-Atmosphere System (EPIC) took place in the fall of 2001. Coupled ocean-atmosphere models have difficulty in properly representing the seasonal cycle in this region (Raymond et al 2004), and EPIC was designed to gather information that would lead to improvements in the understanding the processes at work in this region and their representation in coupled models. During EPIC, the NOAA research ship Ron Brown spent three weeks near 10 degrees North latitude, 95 degrees West longitude in the heart of the East Pacific intertropical convergence zone (ITCZ). Observations were gathered using precipitation radar and cloud radar mounted aboard the ship, radiosondes launched from the ship and through in-situ measurements of wind, rain, humidity and the upper ocean. Observations were also gathered aboard the NSF research ship New Horizon and two aircraft (the NOAA P-3 and NCAR C-130), and by the tropical ocean atmosphere (TAO) buoy array which was supplemented by additional buoys during EPIC.

This webpage describes an integrated dataset that combines shipboard observations with satellite data and products derived from reanalyses. Here the large data volume of the raw data products has been reduced by averaging these observations over three hour intervals and averaging in the vertical as appropriate. Where the interval between successive observations exceeds three hours, linear interpolation has been used. In addition, the integrated dataset supplies a complete set of forcings for a single column model (SCM) or cloud resolving model (CRM). In fact, it can be run in its present form by the single column version of the Community Atmosphere Model (CAM -- the single column model is called SCAM). The observations and forcings are presented below grapically along with a description of their sources, processing and references to the meteorological literature where appropriate. Note that the presence of both a cloud and precipitation radar during EPIC provides a valuable constraint for the representation of both clouds and precipitation in SCMs and CRMs.

This integrated dataset has been used to force and evaluate simulations of EPIC ITCZ using a cloud resolving model, the System for Atmospheric Modeling (SAM), and a single column model, SCAM. The simulations using SAM are described on an additional webpage: SAM simulations of EPIC ITCZ. Please note that these results are preliminary and only intended as an initial validation of the EPIC ITCZ single column forcings. They should not be further disseminated or referenced in presentations or publications until we have more time to evaluate and understand the forcings and the model's performance more completely.


Single Column Forcings

The following fields supply a complete set of forcings for SCAM, the single column version of the Community Atmosphere Model, when it is set up to run using an IOP forcing dataset. SCAM should be able to run using the netcdf file (link above at left) without alteration. Other single column and cloud resolving models should be able to run using these forcings as well, although the details of how the forcings are input will likely differ across models.

The forcings are mainly taken from in situ observations, except as specified below. The large-scale horizontal advective tendencies of temperature and humidity have been computed from ERA-40 using the ERA-40 temperature, humidity and winds by a semi-Lagrangian technique. The profile of large-scale vertical motion (omega) has a fixed shape in the vertical that is taken from the time-averaged ERA-40 vertical motion profile during this period. This profile has been scaled so that the resulting large-scale vertical advective tendency of temperature gives rise to a closed vertically-integrated diagnostic dry static energy (DSE) budget over a three hour period surrounding each time in the integrated dataset. This diagnostic budget is constructed using the following terms (along with their origin in parenthesis): storage (radiosonde temperature), radiation (ISCCP FD radiative fluxes at surface and top of atmosphere), latent heating (radar-derived precipitation using TRMM PR calibration for Z-R relationship, shown as prec_pr below), large-scale horizontal advection (ERA-40), and large-scale vertical advection (ERA-40 mean vertical motion acting on radiosonde DSE profile and scaled to close DSE budget).

In addition to these efforts to close the vertically-integrated dry static energy budget, the large-scale horizontal advective tendency of humidity (HADVQ) has been modified to remove the three-day running mean residual of the vertically-integrated moist static energy (MSE) budget. This running-mean MSE budget residual has been removed by scaling the characteristic vertical profile of HADVQ. (This vertical profile is the mean of the product of the time-varying vertical integral of HADVQ with the vertically- and time-varying HADVQ.) After this adjustment, the time-mean residual of the vertically-integrated moist static energy budget is approximately 5 W/m2.

lat (Latitude)

lat= 10 degree_north

lon (Longitude)

lon= -95 degree_east

nbdate (Base Date)

nbdate= 010912 yymmdd

Note that only two digit year is permitted. Actual year for the dataset is 2001.

phis (Surface Geopotential)

phis= 0 m2/s2

tsec (Time in seconds after 00Z on nbdate)

Ps (Surface Pressure (ERA-40))

Mean surface pressure for EPIC ITCZ from ERA-40. ECMWF ERA-40 data used in this project have been obtained from the ECMWF Data Server.

Ptend (Surface pressure tendency (ERA-40))

ECMWF ERA-40 data used in this project have been obtained from the ECMWF Data Server.

Tg (Observed Sea Surface Temperature (5m depth, R/V Ron Brown))

tsg water temperature (5 m depth). Collected aboard the R/V Ron Brown during the EPIC-ITCZ experiment, Sept-Oct 2001. Data processed by Chris Fairall (NOAA/ESRL). Time-averaged from original five minute resolution.

shflx (Observed bulk sensible heat flux (R/V Ron Brown))

Observed bulk sensible heat flux. Collected aboard the R/V Ron Brown during the EPIC-ITCZ experiment, Sept-Oct 2001. Data processed by Chris Fairall (NOAA/ESRL). Time-averaged from original five minute resolution.

lhflx (Observed bulk latent heat flux (R/V Ron Brown))

Observed bulk latent heat flux. Collected aboard the R/V Ron Brown during the EPIC-ITCZ experiment, Sept-Oct 2001. Data processed by Chris Fairall (NOAA/ESRL). Time-averaged from original five minute resolution.

Ts (Observed Surface Air Temperature (15.5m height, R/V Ron Brown))

Collected aboard the R/V Ron Brown during the EPIC-ITCZ experiment, Sept-Oct 2001. Data processed by Chris Fairall (NOAA/ESRL). Time-averaged from original five minute resolution.

qs (Observed Surface Air Specific Humidity (15.5m height, R/V Ron Brown))

Collected aboard the R/V Ron Brown during the EPIC-ITCZ experiment, Sept-Oct 2001. Data processed by Chris Fairall (NOAA/ESRL). Time-averaged from original five minute resolution.

u (Zonal Wind (radiosondes))

Processed by Walt Petersen. Launched from R/V Ron Brown. Interpolated in time and space to the time-height grid used here. Missing data has been filled by nearest-neighbor interpolation.

v (Meridional Wind (radiosondes))

Processed by Walt Petersen. Launched from R/V Ron Brown. Interpolated in time and space to the time-height grid used here. Missing data has been filled by nearest-neighbor interpolation.

omega (Vertical Pressure Velocity (Derived))

Shape of omega is based on time-averaged ERA40 omega profile. Amplitude is scaled to close the vertically-integrated dry static energy budget over each three hour period centered around the specified time. Derived by Peter Blossey (UW). ECMWF ERA-40 data used in this project have been obtained from the ECMWF Data Server.

T (Absolute temperature (Radiosonde))

Processed by Walt Petersen. Launched from R/V Ron Brown. Interpolated in time and space to the time-height grid used here. Missing data has been filled by nearest-neighbor interpolation.

q (Specific Humidity (Radiosonde))

Processed by Walt Petersen. Launched from R/V Ron Brown. Interpolated in time and space to the time-height grid used here. Missing data has been filled by nearest-neighbor interpolation.

divT (Horizontal Advective Temperature Tendency (ERA-40))

Computed from ERA-40 fields using a semi-Lagrangian technique by Peter Blossey (UW). ECMWF ERA-40 data used in this project have been obtained from the ECMWF Data Server.

divq (Adjusted Horizontal Advective Humidity Tendency (ERA-40))

Computed from ERA-40 fields using a semi-Lagrangian technique by Peter Blossey (UW). Adjusted to remove the three day running-mean residual from vertically-integrated moist static energy budget. ECMWF ERA-40 data used in this project have been obtained from the ECMWF Data Server.

divq_raw (Horizontal Advective Specific Humidity Tendency (ERA-40))

Computed from ERA-40 fields using a semi-Lagrangian technique by Peter Blossey (UW). ECMWF ERA-40 data used in this project have been obtained from the ECMWF Data Server.


Additional Observations

The following observations are intended to supplement the above observations and derived fields. These fields provide additional information about the conditions during EPIC ITCZ and can be used as additional constraints on simulations using the above forcings. Some of these observations have been used in studies of EPIC ITCZ by Raymond et al (2003), Raymod et al (2006) and Zuidema et al (2006). Note that four precipitation timeseries are supplied below. These have been derived from the C-band precipitation radar data by Rob Cifelli (CSU) and use four different, plausible relationships between radar reflectivity and rainrate (termed Z-R relationships, where Z represents radar reflectivity and R rainrate). The single column forcings above are based on the prec_pr dataset, whose calibration is based on an analysis of TRMM precipitation radar data over the EPIC ITCZ region over a number of years.

Tskin (Observed Ocean Skin Temperature (0.05m depth, R/V Ron Brown))

Sea Snake Temperature (0.05 m depth). Collected aboard the R/V Ron Brown during the EPIC-ITCZ experiment, Sept-Oct 2001. Data processed by Chris Fairall (NOAA/ESRL). Time-averaged from original five minute resolution.

prec_ship (Observed Precipitation (Rain gauges aboard R/V Ron Brown))

Precipitation estimate for R/V Rob Brown during the EPIC-ITCZ experiment, Sept-Oct 2001. Generated by Frank Bradley (CSIRO). Based on measurements from four optical rain gauges and one IMET siphon gauge, including corrections for wind errors. Time-averaged from original five minute resolution.

areaprec_pr (Area fraction with prec_pr > 0.1 mm/hr)

Radar-derived, area-averaged precipitation rates from C-band radar aboard the R/V Ronald H. Brown. Radar data processed and precipitation timeseries generated by Rob Cifelli (CSU). Based on Z-R relationship Z=222R^1.35 from an analysis of the TRMM precipitation radar over the EPIC-ITCZ domain for July, August and September of the years 1998-2004.

prec_gt (Area-averaged radar-derived precipitation rate. Uses Z=230R^1.25.)

Radar-derived, area-averaged precipitation rates from C-band radar aboard the R/V Ronald H. Brown. Radar data processed and precipitation timeseries generated by Rob Cifelli (CSU). Based on Z-R relationship Z=230R^1.25 (Hudlow, 1978) from the GATE experiment.

prec_pr (Area-averaged radar-derived precipitation rate. Uses Z=222R^1.35.)

Radar-derived, area-averaged precipitation rates from C-band radar aboard the R/V Ronald H. Brown. Radar data processed and precipitation timeseries generated by Rob Cifelli (CSU). Based on Z-R relationship Z=222R^1.35 from an analysis of the TRMM precipitation radar over the EPIC-ITCZ domain for July, August and September of the years 1998-2004.

prec_rt (Area-averaged radar-derived precipitation rate. Uses Z=132R^1.24.)

Radar-derived, area-averaged precipitation rates from C-band radar aboard the R/V Ronald H. Brown. Radar data processed and precipitation timeseries generated by Rob Cifelli (CSU). Based on Z-R relationship Z=132R^1.24 from a calibration of the radar aboard the Ron Brown against the precipitation measurements at the nearest TAO buoy.

prec_c1 (Area-averaged radar-derived precipitation rate. Uses Z=218R^1.60.)

Radar-derived, area-averaged precipitation rates from C-band radar aboard the R/V Ronald H. Brown. Radar data processed and precipitation timeseries generated by Rob Cifelli (CSU). Based on Z-R relationship Z=218R^1.60, derived by Baumgardner using in situ data from the C-130 during EPIC-ITCZ.

cldisccp (Cloud Fraction)

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

toaswdn (Downward Shortwave Flux at TOA (Insolation))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

toaswup (Upward Shortwave Flux at TOA (Full Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

toalwup (Upward Longwave Flux at TOA (Full Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

srfswdn (Downward Shortwave Flux at Surface (Full Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

srflwdn (Downward Longwave Flux at Surface (Full Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

srfswup (Upward Shortwave Flux at Surface (Full Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

srflwup (Upward Longwave Flux at Surface (Full Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

toaswupc (Upward Shortwave Flux at TOA (Clear Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

toalwupc (Upward Longwave Flux at TOA (Clear Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

srfswdnc (Downward Shortwave Flux at Surface (Clear Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

srflwdnc (Downward Longwave Flux at Surface (Clear Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

srfswupc (Upward Shortwave Flux at Surface (Clear Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

srflwupc (Upward Longwave Flux at Surface (Clear Sky))

From ISCCP FD dataset. Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1, respectively, to approximate averages over a 200km square box around 10N, 95W. Available from http://isccp.giss.nasa.gov/. When using the ISCCP FD dataset, please reference:Zhang et al. (2004).

udopp (Mean zonal wind derived from Doppler Radar)

Wind and divergence fields were derived using data from the C-band Doppler radar aboard the R/V Ron Brown by Brian Mapes (U Miami) and Jialin Lin (NOAA/CIRES). It has been averaged to three hour time resolution for this integrated dataset. See Mapes and Lin (2005) for more information.

vdopp (Mean meridional wind derived from Doppler Radar)

Wind and divergence fields were derived using data from the C-band Doppler radar aboard the R/V Ron Brown by Brian Mapes (U Miami) and Jialin Lin (NOAA/CIRES). It has been averaged to three hour time resolution for this integrated dataset. See Mapes and Lin (2005) for more information.

divg (Divergence of horizontal wind derived from Doppler Radar)

Wind and divergence fields were derived using data from the C-band Doppler radar aboard the R/V Ron Brown by Brian Mapes (U Miami) and Jialin Lin (NOAA/CIRES). It has been averaged to three hour time resolution for this integrated dataset. See Mapes and Lin (2005) for more information.

std_divg (Standard Deviation/Uncertainty of horizontal wind divergence estimate)

Wind and divergence fields were derived using data from the C-band Doppler radar aboard the R/V Ron Brown by Brian Mapes (U Miami) and Jialin Lin (NOAA/CIRES). It has been averaged to three hour time resolution for this integrated dataset. See Mapes and Lin (2005) for more information.

cloudcr (Frequency of Occurrence of Cloud Radar Reflectivity > -45 dBZ)

A vertically-pointing 8.66 mm, 34.6 GHz cloud radar operated aboard the R/V Ron Brown. The data was processed by Paquita Zuidema (U Miami) and has been averaged onto a vertical grid w/250m spacing and three hour time resolution for this integrated dataset. The cloud radar is subject to attenuation at high rainrates. See Zuidema et al (2006) for more information.

wdoppcr (Doppler Velocity from ship-based Cloud Radar (positive upwards))

A vertically-pointing 8.66 mm, 34.6 GHz cloud radar operated aboard the R/V Ron Brown. The data was processed by Paquita Zuidema (U Miami) and has been averaged onto a vertical grid w/250m spacing and three hour time resolution for this integrated dataset. The cloud radar is subject to attenuation at high rainrates. See Zuidema et al (2006) for more information. Note that Doppler velocity includes precipitation fallspeed and may be affected by ship motion.

Zcrbins (Probability of cloud radar reflectivity within this dBZ bin)

A vertically-pointing 8.66 mm, 34.6 GHz cloud radar operated aboard the R/V Ron Brown. The data was processed by Paquita Zuidema (U Miami) and has been averaged onto a vertical grid w/250m spacing and three hour time resolution for this integrated dataset. The cloud radar is subject to attenuation at high rainrates. See Zuidema et al (2006) for more information. Note: The sum of the probabilities at level and time is equal to the area fraction of cloud radar reflectivity > -45 dBZ.

Zprbins (Probability of precipitation radar reflectivity within this dBZ bin)

C-band precipitation radar data processed by Rob Cifelli (CSU). Sum of probablities at any vertical level gives the area fraction of radar echo at that altitude.

isccpbins (ISCCP Cloud Fraction for this pressure and optical depth bin)

ISCCP D1 data obtained from NASA Langley DAAC. For description, see http://isccp.giss.nasa.gov/ and Rossow and Schiffer (1999). Weighted average of ISCCP pixels 3834, 3975 and 3976 with weights 0.5, 0.4 and 0.1. This corresponds approximately to the intersection of these pixels with the areal coverage of the precipitation radar.


References
  • Hudlow, M. D. (1979). Mean rainfall patterns for the three phases of GATE. J. Appl. Meteor., 18, 1656-1669.
  • Mapes, B. E. and J. Lin (2005). Doppler Radar Observations of Mesoscale Wind Divergence in Regions of Tropical Convection. Monthly Weather Review, 133, pp. 1808-1824.
  • Raymond, D. J., G. B. Raga, C. S. Bretherton, J. Molinari, C. Lopez-Carillo and Z. Fuchs (2003). Convective Forcing in the Intertropical Convergence Zone of the Eastern Pacific. Journal of the Atmospheric Sciences, 60, pp. 2064-2082.
  • Raymond, D. J., C. S. Bretherton and J. Molinari (2006). Dynamics of the Intertropical Convergence Zone of the East Pacific. Journal of the Atmospheric Sciences, 63, pp. 582-597.
  • Raymond, D. J., S. K. Esbensen, C. Paulson, M. Gregg, C. S. Bretherton, W. A. Petersen, R. Cifelli, L. K. Shay, C. Ohlmann and P. Zuidema (2004). EPIC2001 and the coupled ocean-atmosphere system of the tropical East Pacific. Bulletin of the American Meteorological Society, 85, pp. 1341-1354.
  • Rossow, W. B. and R. A. Schiffer (1991). ISCCP cloud data products. Bulletin of the American Meteorological Society, 72, pp. 2-20.
  • Zhang, Y., W. B. Rossow, A. A. Lacis, V. Oinas, and M. I. Mishchenko (2004), Calculation of radiative fluxes from the surface to top of atmosphere based on ISCCP and other global data sets: Refinements of the radiative transfer model and the input data. J. Geophys. Res., 109, D19105, doi:10.1029/2003JD004457.
  • Zuidema, P., B. Mapes, J. Lin, C. Fairall and G. Wick (2006). The Interaction of Clouds and Dry Air in the Eastern Tropical Pacific. Journal of Climate, 19, pp. 4531-4544.