The impact of horizontal resolution on moist processes in the ECMWF model

Technical Report · Fri Jan 01 04:00:00 EST 1993

OSTI ID:6465203

Phillips, T J; Corsetti, L C; Grotch, S L

Summer and winter climates simulated at spectral scales T21, T42, T63 and T106 with the ECMWF model are analyzed to determine the impact of changes in horizontal resolution on atmospheric water vapor, clouds, convection, and precipitation. Qualitative changes in Pi many moist processes occur in the transition from spectral T21 to T42, especially in the tropics where atmospheric convection plays a central role. However, the seasonal climate simulations do not show evidence of convergence to an asymptotic climate state at high resolution. Global convective precipitation increases monotonically with resolution, but frontal precipitation, precipitable water, and cloud cover display a qualitatively different pattern; after undergoing abrupt reductions in the transition from T21 to T42, their global averages show relative increases at finer resolutions. Precipitable water and cloud cover also display a seasonal asymmetry in their responses to increasing resolution.The comparative insensitivity of global cloud cover to resolution is mainly a consequence of compensating tendencies of clouds in different regions. With increasing resolution, decreases in lowlatitude clouds that result from drying of the tropical atmosphere are partially offset by increases in high-latitude clouds associated with enhanced relative humidity in response to an intensifying extratropical cold bias. The large-scale tropical moist processes are modeled more realistically at T21 than in the finer-resolution simulations, wherein anomalous seasonal climatic features such as a double ITCZ and underdeveloped summer monsoon circulation are evident. Although some of these anomalies might ameliorate if the physical parameterizations were suitably tuned,'' these deficiencies may reflect more fundamental problems related to a mismatch between the resolution of the model and the implicit spatial and temporal scales of the parameterizations.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6465203
• Report Number(s): UCRL-ID-112719; PCMDI--8; ON: DE93011718
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110
570000* -- Health & Safety
99 GENERAL AND MISCELLANEOUS
990200 -- Mathematics & Computers
ATMOSPHERIC CIRCULATION
CLIMATE MODELS
CLOUDS
COMPUTERIZED SIMULATION
GENERAL CIRCULATION MODELS
HUMIDITY
MATHEMATICAL MODELS
PRECIPITATION
SEPARATION PROCESSES
SIMULATION