Precipitation AnalysesPrecipitation Analysesfor Climate Applicationsfor Climate Applications

Pingping XiePingping Xie

2013.08.14.2013.08.14.

ObjectivesObjectives

• History and current status

• Illustrate some applications

• List products available

CPC Started as CACCPC Started as CAC

• Climate Analysis Center created 1979

• The CAC missions include the real-time monitoring of climate anomalies along with diagnostic studies relating the anomalies to historical conditions

• Two Branches• Diagnostics Branch • Prediction Branch

The Diagnostics BranchThe Diagnostics Branch• Branch Chief Gene Rasmusson

• Major projects included• Ocean (R.W. Reynolds)• Precipitation and tropical Convection (P.A. Arkin)• Precipitation / Temperature Anomaly (C.F.

Ropelewski)• ENSO Evolution (G. Rasmusson)

• Collecting and constructing observation data key to the success of the projects

• Construction of climate data sets started • Global SST• OLR• Global Precipitation• Station Precipitation and Temperature over Land

Early Efforts Early Efforts in constructing Precip Data Setsin constructing Precip Data Sets

• Station Data • 1979 Started archiving GTS daily station

reports• 1984 Created CAMS (Climate Anomaly

Monitoring System) for monthly precipitation and temperature

• Satellite Estimates• 1979 Developed GPI (GOES Precipitation

Index) technique to derive precipitation estimates from IR data

• 1981 Began routine production of GPI using histograms from GOES

IR• 1982 Started the OLR archive • 1985 Hosted the workshop initiated the

GPCP• 1986 GPCP launched

GPI covers the tropical beltGPI used for climate monitoring

The GPI Global PrecipitationThe GPI Global PrecipitationSample for July 2007Sample for July 2007

• Successful depiction of tropical precipitation• Available only over tropics (40oS-40oN)• Poor performance for non-convectiive precipitation• Smooth spatial structure

SSM/I SSM/I Improves Precipitation EstimatesImproves Precipitation Estimates

• Time • 1987 ~

• Scientific Requirements• Global precipitation data with complete coverage and improved quality

• Technical Developments • PMW instruments aboard Special Sensor Microwave / Imager

• Products • Algorithms / Products developed by many groups• Emission-based algorithms over ocean • Scatter-based algorithms over land • Monthly precipitation estimates on 2.5olat/lon • Available 3-4 months afterwards till ~1999• Real-time monitoring impossible• CAC utilized SSM/I-based precipitation estimates for diagnostics

The SSM/I-Based PrecipitationThe SSM/I-Based PrecipitationSample for July 2007Sample for July 2007

• Estimates extend into extra-tropics

• Improved quality (e.g. over E. Pacific)

• Noisy caused by limited sampling

CAL/VAL/Inter-Comparisons CAL/VAL/Inter-Comparisons for better understanding of the products performancefor better understanding of the products performance

• Time• 1991 – 2000(?)

• Scientific Requirements• Understanding quantitative accuracy of the satellite products• Identifying products with better performance

• Technical Developments• Availability of multiple sets of satellite precipitation estimates

• Activities • Proposing / Participating several intercomparison projects

– GPCP Algorithm Intercomparison Project (AIP)– NASA Precipitation Intercomparison Project (PIP)

• Major conclusions

– MERGING of individual information sources is necessary to improve the quality of precipitation analysis

CMAP CMAP CPC Merged Analysis of PrecipitationCPC Merged Analysis of Precipitation

• Time• 1993 - 1998

• Scientific Requirements• Monitoring and diagnosing climate variability of inter-annual and

intra-seasonal time scales• Verifying reanalyses and climate model simulations

• Technical Developments• Routine production of gauge analysis and satellite estimates• Improved understanding of error structures of input data

• Activities • Developed CPC Merged Analysis of Precipitation

– 2.5olat/lon grid over the entire globe– Monthly / pentad from 1979 to the present– Standard / Real-time versions

CMAP Global PrecipitationCMAP Global PrecipitationSample for July 2007Sample for July 2007

Quest for An Extended RecordQuest for An Extended RecordGauge-based Analysis over Global LandGauge-based Analysis over Global Land

• Time• 1998-2002

• Scientific Requirements• Inter-ENSO variability and long-term Variations

• Technical Developments• Availability of improved station data base (GHCN)

• Activities• Developing OI-based PREC (Precipitation Reconstruction)

» Gauge-based analysis over land 0.5olat/lon grid; monthly, 1948 -

» EOF reconstruction over ocean

Pursuit for high-resolution [1]Pursuit for high-resolution [1]Regional Gauge-Based Analysis over LandRegional Gauge-Based Analysis over Land

• Time• 1996-2004

• Scientific Requirements• Weather-climate linkage • Hydrometeorology (e.g. soil moisture)

• Technical Developments• Availability of daily station archives for several regions• Improved computing / storage capacity

• Activities• Created regional analyses of DAILY precipitation on high-

resolution (0.125o, 0.25o, 0.5o)• Regions include US-MEXICO and Brazil (Higgins and Shi), and

east Asia (Xie et al.)

Pursuit for high-resolution [2]Pursuit for high-resolution [2]High-Resolution Combined Satellite Estimates over the globeHigh-Resolution Combined Satellite Estimates over the globe

• Time:• 1999-2006

• Scientific Requirements:• Weather-climate linkage / Hydrometeorology / MJO / Tropical

Storm

• Technical Developments:• Real-time high-resolution MW estimates from multiple platforms • Real-time high-resolution IR data over the entire globe• High-performance workstation

• Actions• Developed global full-resolution IR system

• Developed CMORPH (CPC Morphing Technique)– MW estimates interpolated through IR cloud moving vectors– 8kmx8km / 60oS-60oN / 30 min interval from Dec.2002

CMORPH PrecipitationCMORPH PrecipitationSample CMORPH for 1998Sample CMORPH for 1998

CPC Unified Precipitation Products [1]CPC Unified Precipitation Products [1]

• Time• 2006

• Scientific Requirements• One single suite of precipitation data sets

serving for most (if not all) applications

• Actions• Started the CPC Unified Precipitation

Products Project

CPC Unified Precipitation Products [2]CPC Unified Precipitation Products [2]• Overall Goals

• To create a single suite of unified precipitation products for various global / regional applications

• To improve the quantitative accuracy and consistency of the products

• Components• An archive of quality controlled station reports

» Monthly, Daily, Hourly precipitation• A collection of satellite-based precipitation estimates

» Precipitation estimates from individual platforms » Combined satellite estimates (CMORPH)

• A suite of precipitation analyses» Gauge-based, gauge-satellite merged» Monthly, Pentad, Daily, Hourly» Global, Regional » Retrospective, Real-time » State-of-the-art objective techniques

• Short-term Goals

• Gauge-based analysis of daily precipitation over global land• Gauge-satellite merged analysis of daily precipitation over the entire globe

CPC Unified Precipitation Products [3]CPC Unified Precipitation Products [3]The Global Daily Gauge AnalysisThe Global Daily Gauge Analysis

• >30K station reports

• Enhanced networks over US, Mexico, Brazil, Australia

• GTS elsewhere

• Optimal Interpolation (OI) with orographic correction

(Xie et al. 2007)

• 0.5olat/lon grid over global land

• Daily fields from 1979 to present

• Real-time operations

• Finished development / construction

CPC Unified Precipitation Products [4]CPC Unified Precipitation Products [4]Gauge Station DistributionGauge Station Distribution

Daily reports from over 30,000 stations worldwide Distributed unevenly with more gauges over US, Brazil, Australia, and

Europe Gauge reports available only from <400 Indian stations through GTS

CPC Unified Precipitation Products [5]CPC Unified Precipitation Products [5]Example of Daily Gauge Analysis for July 1, 2003Example of Daily Gauge Analysis for July 1, 2003

Major precipitation activities well depicted with reasonable details

CPC Unified Precipitation Products [6]CPC Unified Precipitation Products [6]Gauge-Satellite Merged Analysis of Global Daily PrecipitationGauge-Satellite Merged Analysis of Global Daily Precipitation

• Combining daily gauge analysis with CMORPH

• Prototype objective algorithm developed to define the

analysis in two steps

• Removing the CMORPH bias through comparison with gauge

• Combining bias-corrected CMORPH with gauge through OI

• Merged analysis consistent with gauge analysis

• 0.25olat/lon grid over the entire globe

• Daily fields from 2000 to the present

CPC Unified Precipitation Products [7]CPC Unified Precipitation Products [7]Sample gauge and merged analyses for August 2, 2007Sample gauge and merged analyses for August 2, 2007

CPC Unified Precipitation Products [8]CPC Unified Precipitation Products [8]Sample merged analyses for June, 2008Sample merged analyses for June, 2008

• JJA Mean for 1998 – 2010

• Spatial pattern of precipitation, especially that associated with topography, well reproduced by the reanalyses

• Larger oceanic precipitation in CFSR and ERA-I

• Weaker precipitation over mid-latitude compared to the CMORPH

• Heavier rainfall over Maritime-continent

Applications [1]Applications [1] Evaluation of Reanalyses JJA Precip.Evaluation of Reanalyses JJA Precip.

• Standard deviation of 24 hourly means for 1998-2010 (mm/day)

• Diurnal amplitude in CFSR is very similar to that in the observations but presents smaller / larger over ocean, extra-tropical land / tropical land

• Diurnal amplitude in MERRA is generally smaller than that in the observations over tropics and extra-tropics in northern hemisphere and is almost diminished over extra-tropics in southern hemisphere

Applications [2]Applications [2] Precipitation Diurnal CyclePrecipitation Diurnal Cycle

• Amplitude (mm/day) color shading

• Arrow timing (LST) of maximum hourly precipitation(N=00; E=06; S=12; W=18)

• Spatial pattern of amplitude in association with land / sea contrasts

• CFSR represent minimum amplitude over ocean along coast lines

• Phase in general agreement with observations

Applications [3]Applications [3] Precipitation Diurnal Cycle over MaritimePrecipitation Diurnal Cycle over Maritime

• Peak in the reanalyses comes earlier

• Amplitude in the reanalyses is larger / smaller over tropical land / ocean

Applications [4]Applications [4] Diurnal Cycle over Four Selected RegionsDiurnal Cycle over Four Selected Regions

• Longitude section (X-axis) of diurnal evolution (Y-axis) along 40oN over CONUS

• Diurnal cycle (Y-axis) repeated twice

• Precipitation starts from the eastern Rocky around early afternoon (20GMT), traveling eastward and reaching 90oW late afternoon the next day

• Diurnal cycle over land east of 90oW presents fixed phase, opposite to that of precipitation over nearby ocean

• Neither CFSR nor MERRA captures this diurnal variation patterns very well

Applications [5]Applications [5] Diurnal Cycle over CONUSDiurnal Cycle over CONUS

Comparisons between instantaneous SSS from Aquarius with precipitation averaged over different periods ending at the SSS observation times

Data collected over central Pacific [10oS-10oN; 180o-160oW] In general, SSS decreases with P Better agreement between SSS and P averaged over a longer period

Applications [6]Applications [6] Precipitation and SSS over Central PacificPrecipitation and SSS over Central Pacific

Applications [7]Applications [7] Driving Hydrological ModelsDriving Hydrological Models

Courtesy of Y.Zhang et al. of OU

Data Sets AvailableData Sets AvailablePrecipitationPrecipitation

CPC Merged Analysis of Precipitation (CMAP) Monthly / pentad from 1979 to the present 2.5olat/lon over the entire globe

Monthly global gauge analysis (PREC/L) monthly from 1948 to the present 0.5olat/lon over the global land

Daily global gauge analysis (CPC Unified) global land: 0.5olat/lon from 1979 CONUS: 0.125olat/lon from 1948

CMORPH satellite estimates

8km x 8km over the globe from 60oS-60oN 30-min interval from Jan.1, 1998 to the present Satellite-only and bias-corrected versions

Thanks !Thanks !