Application of MJO Simulation Diagnostics to Climate Models

The ability of eight climate models to simulate the Madden-Julian oscillation (MJO) is examined using diagnostics developed by the U.S. Climate Variability and Predictability (CLIVAR) MJO Working Group. Although the MJO signal has been extracted throughout the annual cycle, this study focuses on the boreal winter (November-April) behavior. Initially, maps of the mean state and variance and equatorial space-time spectra of 850-hPa zonal wind and precipitation are compared with observations. Models best represent the intraseasonal space-time spectral peak in the zonal wind compared to that of precipitation. Using the phase-space representation of the multivariate principal components (PCs), the life cycle properties of the simulated MJOs are extracted, including the ability to represent how the MJO evolves from a given subphase and the associated decay time scales. On average, the MJO decay (e-folding) time scale for all models is shorter (~20- 29 days) than observations (~31 days). All models are able to produce a leading pair of multivariate principal components that represents eastward propagation of intraseasonal wind and precipitation anomalies, although the fraction of the variance is smaller than observed for all models. In some cases, the dominant time scale of these PCs is outside of the 30-80-day band. Several key variables associated with the model's MJO are investigated, including the surface latent heat flux, boundary layer (925 hPa) moisture convergence, and the vertical structure of moisture. Low-level moisture convergence ahead (east) of convection is associated with eastward propagation in most of the models. A few models are also able to simulate the gradual moistening of the lower troposphere that precedes observed MJO convection, as well as the observed geographical difference in the vertical structure of moisture associated with the MJO. The dependence of rainfall on lower tropospheric relative humidity and the fraction of rainfall that is stratiform are also discussed, including implications these diagnostics have for MJO simulation. Based on having the most realistic intraseasonal multivariate empirical orthogonal functions, principal component power spectra, equatorial eastward propagating outgoing longwave radiation (OLR), latent heat flux, low-level moisture convergence signals, and vertical structure of moisture over the Eastern Hemisphere, the superparameterized Community Atmosphere Model (SPCAM) and the ECHAM4/Ocean Isopycnal Model (OPYC) show the best skill at representing the MJO.open1149

Estimate of the Cloud and Aerosol Effects on the Surface Radiative Flux Based on the Measurements and the Transfer Model Calculations. Part 1: Shortwave Forcing at Tateno, Japan

In order to estimate the annual surface shortwave forcing by clouds+aerosols and aerosols, the shortwave flux from pyrheliometer and pyranometer measurements, atmospheric profiles from the radiosonde measurements, and aerosol optical properties retrieved from sky radiometer measurements were integrated with high-accuracy transfer model calculations. Clear-sky flux was defined from transfer calculations for a pure Rayleigh-scattering atmosphere, with measured temperature and humidity profiles by radiosonde observations. Monthly variation of the clear-sky flux due to the temperature and water vapor variation was 10-30 Wm(-2). Cloud+aerosol forcing was defined by the difference between the observed flux and the clear-sky flux (positive downward). The annual mean values of the cloud+aerosol surface shortwave forcing was estimated as -81 Wm(-2), which corresponds to about 24 % of the insolation. The aerosol-sky flux is defined with the transfer calculation using the aerosol optical depth retrieved from the sky radiometer measurements. Aerosol forcing was obtained from the differences between the clear-sky flux and the aerosol-sky flux. The mean direct aerosol forcing for 1996, except for March and April, was estimated as -18 Wm(-2), about 6 % of the insolation. We also performed a sensitivity study of the aerosol-sky flux by varying the weight fraction of soot in aerosols. Among the selected soot fraction, the best estimates were obtained as 10 % for January, February and July, 20 % for October through December, 5 % for May, June and August, and 0 % for September. These values are close to the measured seasonal variations of soot fraction in previous studies. Surface flux calculation with the retrieved aerosol size distributions performed no better than those with the LOWTRAN 7 urban model size distribution, especially in the summer months when the water vapor column amount was large. The necessity of further examination of retrieval methods of aerosol optical properties, using sky radiometer measurements, was suggested.雲とエアロゾルの地表面短波放射強制力の年間値を見積もるために、館野における精度のよい短波放射観測値、ラジオゾンデ観測値およびスカイラジオメター観測によるエアロゾルの光学的特性値を用いて高精度放射伝達計算を行なった。晴天フラックスは、ラジオゾンデ観測による温度湿度プロファイルを用いた純粋なレイリー散乱大気についての計算により定義した。水蒸気と温度プロファイルによる晴天フラックスの月変化は10-30Wm(-2)であった。雲とエアロゾルによる地表面短波放射強制力はフラックス観測値と晴天フラックスとの差によって定義した。1996年の年間平均値は-81Wm(-2)であり、大気上端の太陽入射の約24%に当たる。一方、エアロゾル強制は、スカイラジオメター観測によるエアロゾルの光学的厚さを用いた大気フラックスの計算値と晴天フラックスとの差によって求めた。3-4月を除く年間平均値は-18Wm(-2)で、6%にあたる。エアロゾルに含まれる煤の割合に対する感度実験の結果、1月、2月、7月は10%、10-12月は20%、5月、6月、8月は5%、9月は0%の煤の割合が推定された。この値は、これまでに観測されている煤の割合や都市分布と風向の関係と概ね一致する。ただし、スカイラジオメターから求めたエアロゾルの粒径分布を計算に用いると、特に大気水蒸気量の多い夏期において推定値の誤差が拡大した。スカイラジオメター観測データを用いたエアロゾル粒径分布の推定手法について、今後の詳細な検討の必要性が示唆される

State-of-the-art with regional climate models

Regional climate models are used by a large number of groups, for more or less all regions of the world. Regional climate models are complementary to global climate models. A typical use of regional climate models is to add further detail to global climate analyses or simulations, or to study climate processes in more detail than global models allow. The relationship between global and regional climate models is much akin to that of global and regional weather forecasting models. Over the past 20 years, the development of regional climate models has led to increased resolution, longer model runs, and steps towards regional climate system models. During recent years, community efforts have started to emerge in earnest, which can be expected to further advance the state-of-the-art in regional climate modeling. Applications of regional climate models span both the past and possible future climates, facilitating climate impact studies, information and support to climate policy, and adaptation

観測と放射伝達計算による地表面放射への雲とエアロゾルの影響の見積. Part 1: 館野における短波放射強制力

In order to estimate the annual surface shortwave forcing by clouds+aerosols and aerosols, the shortwave flux from pyrheliometer and pyranometer measurements, atmospheric profiles from the radiosonde measurements, and aerosol optical properties retrieved from sky radiometer measurements were integrated with high-accuracy transfer model calculations. Clear-sky flux was defined from transfer calculations for a pure Rayleigh-scattering atmosphere, with measured temperature and humidity profiles by radiosonde observations. Monthly variation of the clear-sky flux due to the temperature and water vapor variation was 10-30 Wm(-2). Cloud+aerosol forcing was defined by the difference between the observed flux and the clear-sky flux (positive downward). The annual mean values of the cloud+aerosol surface shortwave forcing was estimated as -81 Wm(-2), which corresponds to about 24 % of the insolation. The aerosol-sky flux is defined with the transfer calculation using the aerosol optical depth retrieved from the sky radiometer measurements. Aerosol forcing was obtained from the differences between the clear-sky flux and the aerosol-sky flux. The mean direct aerosol forcing for 1996, except for March and April, was estimated as -18 Wm(-2), about 6 % of the insolation. We also performed a sensitivity study of the aerosol-sky flux by varying the weight fraction of soot in aerosols. Among the selected soot fraction, the best estimates were obtained as 10 % for January, February and July, 20 % for October through December, 5 % for May, June and August, and 0 % for September. These values are close to the measured seasonal variations of soot fraction in previous studies. Surface flux calculation with the retrieved aerosol size distributions performed no better than those with the LOWTRAN 7 urban model size distribution, especially in the summer months when the water vapor column amount was large. The necessity of further examination of retrieval methods of aerosol optical properties, using sky radiometer measurements, was suggested.雲とエアロゾルの地表面短波放射強制力の年間値を見積もるために、館野における精度のよい短波放射観測値、ラジオゾンデ観測値およびスカイラジオメター観測によるエアロゾルの光学的特性値を用いて高精度放射伝達計算を行なった。晴天フラックスは、ラジオゾンデ観測による温度湿度プロファイルを用いた純粋なレイリー散乱大気についての計算により定義した。水蒸気と温度プロファイルによる晴天フラックスの月変化は10-30Wm(-2)であった。雲とエアロゾルによる地表面短波放射強制力はフラックス観測値と晴天フラックスとの差によって定義した。1996年の年間平均値は-81Wm(-2)であり、大気上端の太陽入射の約24%に当たる。一方、エアロゾル強制は、スカイラジオメター観測によるエアロゾルの光学的厚さを用いた大気フラックスの計算値と晴天フラックスとの差によって求めた。3-4月を除く年間平均値は-18Wm(-2)で、6%にあたる。エアロゾルに含まれる煤の割合に対する感度実験の結果、1月、2月、7月は10%、10-12月は20%、5月、6月、8月は5%、9月は0%の煤の割合が推定された。この値は、これまでに観測されている煤の割合や都市分布と風向の関係と概ね一致する。ただし、スカイラジオメターから求めたエアロゾルの粒径分布を計算に用いると、特に大気水蒸気量の多い夏期において推定値の誤差が拡大した。スカイラジオメター観測データを用いたエアロゾル粒径分布の推定手法について、今後の詳細な検討の必要性が示唆される