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The main energy input to the polar regions in winter is the advection of warm, moist air from lower lati-tudes. This makes the polar climate sensitive to the temperature and moisture of extrapolar air. Here, we study this sensi-tivity from an air-mass transformation perspective. We perform simulations of an idealized maritime air mass brought into contact with sea ice employing a three-dimensional large-eddy simulation model coupled to a one-dimensional multilayer sea ice model. We study the response of cloud dynamics and surface warming during the air-mass transformation process to varying initial temperature and humidity conditions of the air mass. We find in all cases that a mixed-phase cloud is formed, initially near the surface but rising continuously with time. Surface warming of the sea ice is driven by downward longwave surface fluxes, which are largely controlled by the temperature and optical depth of the cloud. Cloud tempera-ture, in turn, is robustly constrained by the initial dewpoint temperature of the air mass. Since dewpoint only depends on moisture, the overall result is that surface warming depends almost exclusively on initial humidity and is largely indepen-dent of initial temperature. We discuss possible climate implications of this result-in particular, for polar amplification of surface warming and the role played by atmospheric energy transports.

Changes in land surface albedo and land surface evaporation modulate the atmospheric energy budget by changing temperatures, water vapor, clouds, snow and ice cover, and the partitioning of surface energy fluxes. Here idealized perturbations to land surface properties are imposed in a global model to understand how such forcings drive shifts in zonal mean atmospheric energy transport and zonal mean tropical precipitation. For a uniform decrease in global land albedo, the albedo forcing and a positive water vapor feedback contribute roughly equally to increased energy absorption at the top of the atmosphere (TOA), while radiative changes due to the temperature and cloud cover response provide a negative feedback and energy loss at TOA. Decreasing land albedo causes a northward shift in the zonal mean intertropical convergence zone (ITCZ). The combined effects on ITCZ location of all atmospheric feedbacks roughly cancel for the albedo forcing; the total ITCZ shift is comparable to that predicted for the albedo forcing alone. For an imposed increase in evaporative resistance that reduces land evaporation, low cloud cover decreases in the northern midlatitudes and more energy is absorbed at TOA there; longwave loss due to warming provides a negative feedback on the TOA energy balance and ITCZ shift. Imposed changes in land albedo and evaporative resistance modulate fundamentally different aspects of the surface energy budget. However, the patterns of TOA radiation changes due to the water vapor and air temperature responses are highly correlated for these two forcings because both forcings lead to near-surface warming.

Northward fluxes of moisture and sensible heat into the Arctic affect the atmospheric stability, sea ice and snow cover, clouds, and surface energy budget. Intense moisture fluxes into the Arctic are called moisture intrusions; some can lead to basinwide increases in downward longwave radiation (DLR) at the surface, called downward infrared (IR) events. Using the ERA-Interim reanalysis from 1990 to 2016, this study investigated the time evolution of cloud amount and cloud properties and their impact on the surface radiation fluxes in response to Arctic moisture intrusions and downward IR events during winter for better understanding of the Arctic moisture intrusions. A composite analysis revealed several key features: moisture intrusions produce more clouds and higher cloud liquid and ice water content; positive cloud amount anomalies can persist for over 10 days over the Arctic Ocean during downward IR events; positive high-level and middle-level cloud anomalies are evident in the early stage, and positive low-level cloud anomalies are evident in the late stage. Greater clear-sky DLR and longwave cloud radiative forcing (CRF) over the Arctic Ocean accompany the greater all-sky DLR during the downward IR events. Greater clear-sky DLR can be attributed to higher air temperatures and higher total column water vapor, while greater longwave CRF is the result of larger cloud amount and cloud water content. Longwave CRF anomalies account for approximately 40% of the all-sky DLR anomalies.

The effect of global climate model (GCM) time step-which also controls how frequently global and embedded cloud resolving scales are coupled-is examined in the Superparameterized Community Atmosphere Model ver 3.0. Systematic bias reductions of time-mean shortwave cloud forcing (-10 W/m2) and longwave cloud forcing (-5 W/m2) occur as scale coupling frequency increases, but with systematically increasing rainfall variance and extremes throughout the tropics. An overarching change in the vertical structure of deep tropical convection, favoring more bottom-heavy deep convection as a global model time step is reduced may help orchestrate these responses. The weak temperature gradient approximation is more faithfully satisfied when a high scale coupling frequency (a short global model time step) is used. These findings are distinct from the global model time step sensitivities of conventionally parameterized GCMs and have implications for understanding emergent behaviors of multiscale deep convective organization in superparameterized GCMs. The results may also be useful for helping to tune them.

The effect of global climate model (GCM) time step-which also controls how frequently global and embedded cloud resolving scales are coupled-is examined in the Superparameterized Community Atmosphere Model ver 3.0. Systematic bias reductions of time-mean shortwave cloud forcing (-10 W/m2) and longwave cloud forcing (-5 W/m2) occur as scale coupling frequency increases, but with systematically increasing rainfall variance and extremes throughout the tropics. An overarching change in the vertical structure of deep tropical convection, favoring more bottom-heavy deep convection as a global model time step is reduced may help orchestrate these responses. The weak temperature gradient approximation is more faithfully satisfied when a high scale coupling frequency (a short global model time step) is used. These findings are distinct from the global model time step sensitivities of conventionally parameterized GCMs and have implications for understanding emergent behaviors of multiscale deep convective organization in superparameterized GCMs. The results may also be useful for helping to tune them.

The United States Navy is the Department of Defense s main source for standard meteorological and oceanographic predictions (METOC). At the heart of these predictions are the short-to-medium range weather forecasts produced by the Navy Operational Global Atmospheric Prediction System (NOGAPS). In addition to providing weather forecasts, this system provides forcing (i.e. surface fluxes) to the oceanographic prediction systems. Given the prominent role surface fluxes play in both these systems, it is vital they be properly simulated by NOGAPS. Presently, there are significant shortcomings in the NOGAPS simulation of the surface energy budget over the ocean. These shortcomings are mostly associated with mean surface latent and net solar heat flux biases that can be as large as 50 Wm-2 or more in a number of tropical/subtropical areas. The long term goal of this research is to determine the underlying causes for these shortcomings in order to: 1) enhance NOGAPS physical representation of the atmosphere and extend the skill of its medium range weather predictions, and 2) improve the skill of the oceanographic and coupled prediction systems via the improved simulation and prediction of the surface energy budget.

The United States Navy is the Department of Defense's main source for standard meteorological and oceanographic (METOC) predictions. At the heart of these predictions are the short-to-medium range weather forecasts produced by the Navy Operational Global Atmospheric Prediction System (NOGAPS; Hogan and Rosmond, 1991). Surface flux fields from NOGAPS forecasts are used as input to the oceanographic prediction systems. These systems include: (1) the Thermodynamic Ocean Prediction System, (2) the Polar Ice Prediction System, and (3) the Third Generation Wave Model. Given the prominent role surface fluxes play in these systems, it is clear that their proper simulation by NOGAPS is vital. Presently, there are significant shortcomings in the NOGAPS simulation of the net surface shortwave flux (long-term mean biases greater than 50 Wm-2 in many tropical/subtropical areas), as well as other surface heat flux components (similar size biases in the latent and net surface heat fluxes). The long term goal of this research is to determine the underlying causes for these shortcomings and help implement modifications for improvement in order to: (1) enhance this model's physical representation of the atmosphere and extend the skill of its medium range weather predictions, and (2) improve the skill of the oceanographic and coupled prediction systems via the improved simulation and prediction of the surface energy budget. The objectives of this research are to analyze and improve the model representations of the surface shortwave flux and the associated radiative-convective processes., See also ADM002252.