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- Author or Editor: C. J. Kok x
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Abstract
For six consecutive seasons around the 1982–83 El Niño event the relation between observed anomalies in atmospheric circulation patterns and anomalies in various forcing mechanisms is diagnosed. A linear model is used in an attempt to simulate atmospheric anomalies as a stationary response to observed anomalies in tropical diabatic heating, mountain and transient eddy effects. The response to forcing by transient eddies is large for all seasons and is significantly correlated with observed anomalies. To what extent observed anomalous transient eddy activity is related to anomalous conditions at the earth’s surface can not be deduced from these experiments.
The midlatitude effect of tropical heating are found to be small oven during the mature phase of the 1982–83 warming event. However these results are critically dependent on the exact location of the zero wind line. The effect of the orography caused by observed anomalies in zonal mean westerly winds is small in general. In one season, when El Niño is at its maximum, the effect is comparable in magnitude to that of the transient eddies.
Abstract
For six consecutive seasons around the 1982–83 El Niño event the relation between observed anomalies in atmospheric circulation patterns and anomalies in various forcing mechanisms is diagnosed. A linear model is used in an attempt to simulate atmospheric anomalies as a stationary response to observed anomalies in tropical diabatic heating, mountain and transient eddy effects. The response to forcing by transient eddies is large for all seasons and is significantly correlated with observed anomalies. To what extent observed anomalous transient eddy activity is related to anomalous conditions at the earth’s surface can not be deduced from these experiments.
The midlatitude effect of tropical heating are found to be small oven during the mature phase of the 1982–83 warming event. However these results are critically dependent on the exact location of the zero wind line. The effect of the orography caused by observed anomalies in zonal mean westerly winds is small in general. In one season, when El Niño is at its maximum, the effect is comparable in magnitude to that of the transient eddies.
Abstract
Using a two-level linear, steady state model, we diagnose the 40-day mean response of a GCM to a tropical sea surface temperature (SST) anomaly. The time-mean anomalies produced by the GCM are simulated as linear response to the anomalous hemispheric distributions of latent heating, sensible heating and transient eddy forcing. Also, the anomalous effect of mountains, caused by anomalies in the zonal mean surface wind is taken into account. All anomalies are defined as the difference between perturbation and control runs. For our analysis, we have taken the tropical Atlantic SST anomaly experiment performed by Rowntree.
We have compared the linear model's response in temperature at 600 mb and winds at 400 mb with the same anomalous quantities produced by the GCM. The similarity between the time-mean anomalies of the GCM experiment and the linear model's response is very high. The pattern correlation coefficients are between 0.6 and 0.7 in the region between 30°N and 60°N. The response to each of the anomalous forcings separately is positively correlated with the GCM anomaly pattern. The amplitude of the response to anomalous forcing by transient eddies is a factor of two or three larger than the effects of anomalous sensible and latent heating. The anomalous effect of the orography is negligible.
Although intended to be a tropical SST anomaly GCM experiment, the difference between control and perturbation runs does not seem to be directly related to tropical heating near the SST anomaly. Instead, most of the forcing of anomalies in the midlatitudes took place in the midlatitudes itself and, in particular, the remote effects of forcing by tropical latent heat sources were minor.
Abstract
Using a two-level linear, steady state model, we diagnose the 40-day mean response of a GCM to a tropical sea surface temperature (SST) anomaly. The time-mean anomalies produced by the GCM are simulated as linear response to the anomalous hemispheric distributions of latent heating, sensible heating and transient eddy forcing. Also, the anomalous effect of mountains, caused by anomalies in the zonal mean surface wind is taken into account. All anomalies are defined as the difference between perturbation and control runs. For our analysis, we have taken the tropical Atlantic SST anomaly experiment performed by Rowntree.
We have compared the linear model's response in temperature at 600 mb and winds at 400 mb with the same anomalous quantities produced by the GCM. The similarity between the time-mean anomalies of the GCM experiment and the linear model's response is very high. The pattern correlation coefficients are between 0.6 and 0.7 in the region between 30°N and 60°N. The response to each of the anomalous forcings separately is positively correlated with the GCM anomaly pattern. The amplitude of the response to anomalous forcing by transient eddies is a factor of two or three larger than the effects of anomalous sensible and latent heating. The anomalous effect of the orography is negligible.
Although intended to be a tropical SST anomaly GCM experiment, the difference between control and perturbation runs does not seem to be directly related to tropical heating near the SST anomaly. Instead, most of the forcing of anomalies in the midlatitudes took place in the midlatitudes itself and, in particular, the remote effects of forcing by tropical latent heat sources were minor.
The Mixed-Phase Arctic Cloud Experiment (M-PACE) was conducted from 27 September through 22 October 2004 over the Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) on the North Slope of Alaska. The primary objectives were to collect a dataset suitable to study interactions between microphysics, dynamics, and radiative transfer in mixed-phase Arctic clouds, and to develop/evaluate cloud property retrievals from surface-and satellite-based remote sensing instruments. Observations taken during the 1977/98 Surface Heat and Energy Budget of the Arctic (SHEBA) experiment revealed that Arctic clouds frequently consist of one (or more) liquid layers precipitating ice. M-PACE sought to investigate the physical processes of these clouds by utilizing two aircraft (an in situ aircraft to characterize the microphysical properties of the clouds and a remote sensing aircraft to constraint the upwelling radiation) over the ACRF site on the North Slope of Alaska. The measurements successfully documented the microphysical structure of Arctic mixed-phase clouds, with multiple in situ profiles collected in both single- and multilayer clouds over two ground-based remote sensing sites. Liquid was found in clouds with cloud-top temperatures as cold as −30°C, with the coldest cloud-top temperature warmer than −40°C sampled by the aircraft. Remote sensing instruments suggest that ice was present in low concentrations, mostly concentrated in precipitation shafts, although there are indications of light ice precipitation present below the optically thick single-layer clouds. The prevalence of liquid down to these low temperatures potentially could be explained by the relatively low measured ice nuclei concentrations.
The Mixed-Phase Arctic Cloud Experiment (M-PACE) was conducted from 27 September through 22 October 2004 over the Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) on the North Slope of Alaska. The primary objectives were to collect a dataset suitable to study interactions between microphysics, dynamics, and radiative transfer in mixed-phase Arctic clouds, and to develop/evaluate cloud property retrievals from surface-and satellite-based remote sensing instruments. Observations taken during the 1977/98 Surface Heat and Energy Budget of the Arctic (SHEBA) experiment revealed that Arctic clouds frequently consist of one (or more) liquid layers precipitating ice. M-PACE sought to investigate the physical processes of these clouds by utilizing two aircraft (an in situ aircraft to characterize the microphysical properties of the clouds and a remote sensing aircraft to constraint the upwelling radiation) over the ACRF site on the North Slope of Alaska. The measurements successfully documented the microphysical structure of Arctic mixed-phase clouds, with multiple in situ profiles collected in both single- and multilayer clouds over two ground-based remote sensing sites. Liquid was found in clouds with cloud-top temperatures as cold as −30°C, with the coldest cloud-top temperature warmer than −40°C sampled by the aircraft. Remote sensing instruments suggest that ice was present in low concentrations, mostly concentrated in precipitation shafts, although there are indications of light ice precipitation present below the optically thick single-layer clouds. The prevalence of liquid down to these low temperatures potentially could be explained by the relatively low measured ice nuclei concentrations.
