The Impact of ATOVS Radiance in MERRA Reanalysis

The Impact of ATOVSRadiance in MERRAReanalysisJunye Chen 1,2 , Mike Bosilovich 2 , Franklin Robertson 31: ESSIC/UMD 2: GMAO/GSFC/NASA 3: ESO/MSFC/NASA

Contents The idea of reanalysis was initiated for climate changestudy, but the inhomogeneity issue of reanalysisimpedes the full realization of this goal. The new NASA reanalysis (MERRA), and ongoingefforts to minimize the inhomogeneity in MERRA. The impact of NOAA-15 ATOVS in MERRA.

At the Beginning, the Idea of Reanalysis was Initiatedfor Climate Change Study:“to use a frozen state-of-the-art analysis/forecast system andperform data assimilation using past data” (Kalnay et al. 1996),thus “to produce internally consistent, homogeneous,multivariate data sets for the earth's climate system. … and suchdata sets will be quite useful for studying global climatechange” (Bengtsson and Shukla 1988). A fixed assimilation systemeliminates the inhomogeneity caused by analysis/model change.

Ideally, if both observation and model simulation arenot biased, random errors will be minimized by theanalysis scheme, and there will be no artificial climatetrend in the reanalysis data.In reality, both observation and model are more orless biased. As the global observing system changesalong the time, the reanalysis homogeneity is hard tobe kept, even with fixed model and analysis scheme.

Features in the NASA MERRA reanalysis toDecrease the Side Effect of Observing System Incremental Analysis Updates (IAU) to slowly adjustthe model states toward the observed state. Adaptive Biases Correction to keep temporalhomogeneity in each observation type. Using homogenized radionsonde data fromHaimberger (2007).But the impact of the introductions of New ObservationPlatforms was not addressed.

The impact of changing observing system in reanalysesNOAA15(ATOVS)NOAA16(ATOVS)Cease ofTOVS (?)SSMI

Radiosonde, PIBAL wind, aircraft report, dropsonde, surface land observationPre-sat era stream (PRES)Reduced observing system segment (ROSS) 1GMS & METEOSAT cloud drift wind, ship & buoy observationPAOBTOVSMERRA stream 12SSM/I3Spinup 1ERS surface windWind profilesMERRA stream 24GOES cloud drift windTMI rain5ATOVS (NOAA-15)QuikSCAT surface wind6ATOVS (NOAA-16)GOES SoundersSpinup27MODIS windAIRSMERRA stream 370 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12

ROSS 1 7Pre-sat era stream MERRA stream 1 MERRA stream 2 MERRA stream 3 Patch 1: to correct TOVS etc. impact Patch 2: to correct SSM/I impact Patch 3: to correct scatterometer surface wind impact Patch 4: to correct GEOS cloud drift wind impact Patch 5: to correct ATOVS (NOAA 15) impact Patch 6: to correct ATOVS (NOAA 16) impact Patch 7: to correct AIRS, MODIS impactExtended Homogenized MERRA data• Patches are applied on the MERRA data before the associated new observation, so the MERRA data inearlier period can be adjusted to match with data in later period.• A pre-satellite era stream (1970 – 1979) will be produced, so the MERRA data can be extended to 1970.Including this period is important for climate change trend study, as the long-term trend can be distinguishedfrom natural decadal variation by including the 1976 phase change of PDV into the timeseries (Chen et al.2008).

The impact of NOAA15 (ATOVS)A two year ROSS withholding theNOAA-15 ATOVS radiance data has beenproduced to address the impact of theintroduction of ATOVS data in late 1998.This reanalysis segment is a naturalcontinuation of MERRA at the time beforeNOAA-15 ATOVS data is added, exceptthat the new NOAA-15 data that comesalong will not be assimilated. Bycomparing the original MERRA data withthis NOAA-15_withholding reanalysissegment, a systematic picture of theNOAA-15 impact will be shown.

The impact on cloud amount istightly coupled with surface andTOA radiative fluxes.Color: ave (MERRA – withholding_run)Contour: ave (MERRA)

The precipitation difference between MERRA and NOAA-15 withholding run

The evolution of thezonal meanprecipitation andvertical velocity.Although the omegafiled is a little bitnoisy, clearly it isdriven by theprecipitation field.

Change of moisture mainly in the lower free troposphere

Moisture increment, the additional moisture injected in the system bythe data assimilation process, increases because the assimilation of newmoisture information from NOAA-15 ATOVS data.

Precipitation removes the additional moisture added in by the assimilation.DQVDTMST almost offsets the DQVDTANA.

The temperature change mainly happens in high level and high latitudes.The amplitude of change is quite small in comparison with tendencies.

At most areas, the analysis temperature increment try to coolthe atmosphere which is warmed up by the moisture processdriven by moisture increment.

The additional precipitation from moisture increment warms theatmosphere. The warm effect is almost offset by the negativetemperature increment.

Associated with the introduction of NOAA-15 ATOVS, thehumidity in the lower free atmosphere increases. It is a residual ofthe balance between the moisture increment and precipitation. The additional precipitation releases latent heat, which is almostoffset by the negative change of temperature increment. The residualof this balance drives the large scale overturning circulation andchanges the temperature field over high latitude and high altituderegion.

The EndThank you!