GAPP OBSERVATION NEEDS Dennis P. Lettenmaier Department of Civil and Environmental Engineering University of Washington GAPP PI Meeting Boulder, CO August 31, 2004

Role of observations in the Science and Implementation Plan No specific observation element Lots of discussion in context of model validation, diagnostics, etc Need for collection of observations mentioned in: Overview (Implementation strategies): “New field observations, if necessary, may be developed in the future.” Land memory and variability studies: “… there is a need to acquire and, if necessary, collect new field observations to improve and validate model parameterizations …”, and “The initial priorities for reach in this area within the GAPP program will therefore include: … Initially, improve observations of precipitation in regions of the Americas where data are sparse, such as the mountainous regions of the western United States and northwestern Mexico, as the basis for improving models’ representation of precipitation processes …” Hydrometeorology of orographic systems (“Deliverables”): “Assessment of observational requirements and limitations for mountainous regions”

Observations in the S&I plan (cont.) Warm season precipitation: “The GAPP Implementation strategy is based on improving the observational climatic data base and theoretical understanding of hydrometeorological processes in the core of the North American continental warm season precipitation regime” … “GAPP is funding major enhancements to warm season precipitation observations across the North American Monsoon domain as part of the NAME 2004 Enhanced Observing Period.” CEOP: “The CEOP observation and data collection time period (IGPO 2001) takes advantage of the maturing capabilities of the GEWEX Continental Scale Experiments”. … “As part of its contribution to CEOP, GAPP is providing observations from five high quality in-situ US sites …” Remote sensing: Because satellite derived soil moisture fields are sporadic and prone to uncertainty, producing optimal global fields of soil moisture will require various types of observations to be merged and/or assimilated into sophisticated models to account for the errors and to extend the information in time and space.

Observations in the S&I plan (cont.) Data management: ”The accomplishment of GAPP goals and major science objectives involves the development of a comprehensive and accessible database for the Continental-scale GAPP study area and the establishment of an evolving program of model development that will permit observations and analyses to be extended spatially within GAPP or applied globally with new observations.” … “These data sets will consist primarily of relevant data from existing in-situ, remote sensing, and model output sources and will also include special (surface, upper air, and satellite) meteorological and hydrological observations”

GCIP Strategy regarding observations Lots of observations in the Mississippi basin (which is why it was selected) $ in short supply (even more so than now) Hence use existing data Sellers proposal c. 1995 for an observational element (towers and aircraft transects) was never implemented

GAPP observation strategy (inferred from S&I Plan) Basically the same as GCIP – use someone else’s data Major exception is NAME (but is it PACS or GAPP? – makes no difference for NOAA, but it does for NASA) Challenges in determining the observational needs became greater with increased focus on S/I (vs. weather heritage of GCIP)

Where are the missing links to observations? GAPP has three main science elements – land memory and variability, warm season precipitation, and hydrometeorology (read “precipitation”) in orographic systems (other elements essentially support these areas, or in the case of CEOP, are stand-alone programs to which GAPP is linked) Warm season precipitation is supported by NAME observational program No observation program for land memory and variability, or orographic systems Is this a shortcoming? (where do CALJET and IMPROVE fit into the scheme of things?)`

IMPROVE: Improvement of Microphysical PaRameterization through Observational Verification Experiment Objective: Improve the QPFs produced by MM5, and specifically its bulk microphysical parameterizations, with the aim of also improving QPFs derived from other models, including the Weather Research and Forecast  (WRF) model. Field program: IMPROVE-1 (Washington Offshore Frontal Field Study) -- carried out off the coast of Washington 4 January--14 February 2001. Focus on frontal systems over an oceanic domain with weak sea-surface temperature gradients. Lower boundary is spatially uniform, hence structures of precipitation features can be verified by observations in spite of modest position errors. IMPROVE-2 (Oregon Cascades Orographic Field Study) -- carried out in the Oregon Cascade Mountains 26 November--22 December 2001.  Motivation: In situations where essentially steady flow impinges on a topographic barrier and the upstream conditions are known, the dynamical response is highly deterministic, provided the forecast model can properly resolve the key terrain-forced dynamics. In addition, terrain-forced flow produces large gradients in cloud microphysical variables and processes, providing a good test bed for the model microphysics.

IMPROVE PAPERS (including JAS special issue to appear)

PACJET/CALJET: Pacific Landfalling Jets Experiment/California Land-Falling Jets Experiment Goals: Assess how sensitive mesoscale numerical predictions of flooding rains and windstorms along the [California] coast are to uncertainty in the strength, position, and moisture content of the LLJ 0-18 h before its land fall? Assess how enhanced observations (e.g. coastal, buoy-mounted, or island wind profilers) would improve short-term (0-12 h) QPFs of flooding rains and damaging coastal winds? Provide offshore and coastal observations from the experiment to operational weather forecasters. Determine what atmospheric conditions contribute to the gross underestimates of rainfall from NEXRAD in coastal mountains Provide observations of conditions at land fall for comparison with mesoscale numerical simulations, including detailed measurements of boundary layer conditions offshore and onshore, as well as microphysical measurements related to orographic precipitation enhancement. Experimental Design (CALJET): Experiment period 1 December 1997 to 31 March 1998, during which numerous wind profilers and a cloud radar will be in place along the coast. Special observing period 18 January - 28 February 1998, when NOAA's P-3 and the Univ. of Oklahoma's Doppler on Wheels will be operated out of Monterey, California.

Experimental design (PACJET) Field experiments winters of 2001, 2002, 2003 General design: Network of 915-MHz wind profiling radars along the Pacific coast from northern Oregon to southern California, as well as others in California's central valley and Sierra foothills. Additional focused observations (e.g. Jan-Feb 2003, focused observations along coast north of San Francisco). Some periods have utilized additional advanced-technology instruments, including a polarimetric, Doppler X-band scanning weather radar, a pair of S-band precipitation profiling radars, raindrop disdrometers, and special high-resolution rain gauges. Aircraft: NOAA P-3 (winter 2002; other?)

Challenge to GAPP/CPPA community: Is the absence of an observational element (aside from NAME) a critical shortcoming? If there is a need (which would have to be demonstrated), how is it to be met?