Cooperative Institute for Research in the Atmosphere

About: Cooperative Institute for Research in the Atmosphere is a based out in . It is known for research contribution in the topics: Snow & Data assimilation. The organization has 332 authors who have published 997 publications receiving 38835 citations. The organization is also known as: CIRA.

On water vapor Jacobian in fast radiative transfer model

Abstract: [1] The Community Radiative Transfer Model (CRTM) is a powerful numerical software used for satellite data assimilation and remote sensing applications. Its accuracies in simulating satellite radiances and their gradients relative to water vapor (or Jacobians) are improved through this study when the CRTM includes additional gaseous absorbers. Three water vapor transmittance regression methods (labeled with A–C, respectively) are discussed that differ primarily in vertical coordinates and the application of constraints to smooth vertical structures of the regression coefficients. Method A computes optical depth profiles at fixed pressure levels, whereas method B computes the profiles at fixed levels of the integrated absorber amount. Method C is a derived version of method B with an addition that a polynomial function is applied to the regression coefficients to improve the water vapor Jacobians. The intercomparison focuses on the modeling of 22 sounding channels routinely used at numerical weather prediction (NWP) centers: 9 Atmospheric Infrared Radiance Sounder channels, 4 High-Resolution Infrared Sounder channels, 4 Advanced Microwave Sounding Unit-A channels, and 5 Microwave Humidity Sounder channels. An ensemble of 48 diverse atmosphere profiles at the University of Maryland at Baltimore County was used to test the results. The results were compiled for methods A and C for water vapor line absorption only while keeping the other components the same under the CRTM framework. The comparison quantities include the water vapor Jacobians, temperature Jacobians, and the forward top-of-the-atmosphere brightness temperature (BT). In the infrared, the forward models mean errors are very small (less than 0.03 K) compared to the line-by-line model. Temperature and water vapor Jacobian goodness-of-fit measure values are very small and sufficient for NWP application, except for some dry atmospheric profiles. For the cold and dry atmospheric profiles, method C can significantly improve the water vapor Jacobian profile and remove the unphysical kinks (oscillations) that appear in method A. The improved water vapor Jacobian profile results in the improved temperature Jacobian. For the microwave channels, the forward BTs show very small biases less than 0.1 K for all the channels, and the overall water vapor Jacobian using method A is better than those using method C, especially for warm and wet atmospheric profiles.

A numerical simulation of dryline sensitivity to soil moisture

Abstract: Previous studies have explained dryline movement to be a result of vertical turbulent mixing. Such mixing was shown to efficiently erode the western edge of the shallow moist layer above sloping terrain. Two- and three-dimensional simulations have been used to demonstrate the impact of surface physiography on dryline evolution. Those simulations included changes in vegetation type, vegetation coverage, and soil moisture. In particular, dryline morphology has been shown to be dependent on the horizontal distribution of soil moisture. Modeling studies have also suggested that increases in the low-level horizontal water vapor gradient, associated with a dryline, are a result of frontogenetic forcing. The current study will extend past results by including more sensitivity experiments showing the dependence of dryline morphology on soil moisture. In this paper, the Regional Atmospheric Modeling System was used to simulate the 26 April 1991 central plains dryline. Five simulations were conducted in wh...

Spatiotemporal Characteristics of Seasonal Snow Cover in Northeast Greenland from in Situ Observations

Abstract: In this study, we quantified the spatiotemporal variability and trends in observations of multiple snow characteristics in High Arctic Zackenberg in Northeast Greenland through 18 years. Annual premelt snow-depth observations collected in 2005–2014 along an elevation gradient showed significant differences in snow depth between vegetation types. The seasonal snow cover was characterized by strong interannual variability in the Zackenberg region. Particularly the timing of snow-cover onset and melt, and the annual maximum accumulation, varied up to an order of magnitude between years. Hence, apart from the snow-cover fraction registered annually on 10 June, which exhibits a significant trend of -2.3% per year over the 18-year period, we found little evidence of significant trends in the observed snow-cover characteristics. Moreover, SnowModel results for the Zackenberg region confirmed that the pronounced interannual variability in snow precipitations has persisted in this High Arctic setting sinc...

Future permafrost conditions along environmental gradients in Zackenberg, Greenland

Abstract: . The future development of ground temperatures in permafrost areas is determined by a number of factors varying on different spatial and temporal scales. For sound projections of impacts of permafrost thaw, scaling procedures are of paramount importance. We present numerical simulations of present and future ground temperatures at 10 m resolution for a 4 km long transect across the lower Zackenberg valley in northeast Greenland. The results are based on stepwise downscaling of future projections derived from general circulation model using observational data, snow redistribution modeling, remote sensing data and a ground thermal model. A comparison to in situ measurements of thaw depths at two CALM sites and near-surface ground temperatures at 17 sites suggests agreement within 0.10 m for the maximum thaw depth and 1 °C for annual average ground temperature. Until 2100, modeled ground temperatures at 10 m depth warm by about 5 °C and the active layer thickness increases by about 30%, in conjunction with a warming of average near-surface summer soil temperatures by 2 °C. While ground temperatures at 10 m depth remain below 0 °C until 2100 in all model grid cells, positive annual average temperatures are modeled at 1 m depth for a few years and grid cells at the end of this century. The ensemble of all 10 m model grid cells highlights the significant spatial variability of the ground thermal regime which is not accessible in traditional coarse-scale modeling approaches.

Evaluation of Cloud Shading Effects on the Generation and Modification of Mesoscale Circulations

Abstract: This study presents scale analysis and numerical model evaluations of the impact of cloud shading on (1) the development of sea breeze and thermally induced upslope flows and (2) the generation of mesoscale circulations between cloudy areas adjacent to clear areas. Based on the assumption of modifications of solar and longwave radiation which are typical for some overcast conditions, it was found that the reduction in the first type of circulation is significant and most noticeable in the vertical velocities. In the second case, thermally induced circulations in favorable conditions appear to approach the typical intensity of the sea breeze.