Construction of Vertical Wind Profile from Satellite-Derived Winds for Objective Analysis of Wind Field

During summer Monex-79, a variety of observing systems viz. research ships, research aircrafts, constant pressure balloons and geostationary satellite etc. were deployed, besides the regular conventional observations. The purpose of these additional systems was to make the best possible data for the studies on various aspects of monsoon circulation. The present study is aimed at the construction of vertical wind profile using cloud motion vectors obtained from GOES (I-O) satellite and to examine whether the constructed wind profiles improves the representation of the monsoon system, flow pattern etc. in the objective analysis. For this purpose, climatological normals of the wind field are considered as the initial guess and the objective analyses of the wind field are made with, first using only data from conventional observations over land areas, subsequently including the constructed winds from cloud motion vectors. These analyses are then compared with the standard analyses of wind field obtained from Quick Look Atlas by T. N. Krishnamurti et al. (1979).It is inferred that satellite estimated mean wind profiles show good agreement with the mean wind profiles of the research ships with RMS errors less than 5 mps below 500 hPa and less than 8 mps above 500 hPa. It is further inferred that the inclusion of constructed winds shows a positive impact on the objective analysis and improvement is seen to be more marked in the data-sparse region of the Arabian sea. Analyses which include the constructed winds show better agreement with the standard analysis, than the analyses obtained using only conventional winds. Thus, results of our study suggest that the wind profiles constructed using cloud motion vectors are of potential use in objective analysis to depict the major circulation features over the Indian region.

A New Observation Operator for the Assimilation of Satellite-Derived Relative Humidity:Methodology and Experiments with Three Sea Fog Cases over the Yellow Sea

Assimilation of satellite-derived relative humidity(Satellite-RH)is capable of improving sea fog forecasts by saturating the background in the observed foggy areas.Previous studies have achieved saturation by increasing the moisture only(Method-q).However,this method can lead to large wetting and warming biases within the marine atmospheric boundary layer(MABL).A new method using an RH observation operator(Method-RH)is designed to alleviate these biases by simultaneously adjusting the moisture and the temperature.For comparison,saturation is also achieved by decreasing the temperature only(Method-t).The three Satellite-RH assimilation methods are implemented within the Gridpoint Statistical Interpolation-based three-dimensional variational system and examined for three sea fog cases over the Yellow Sea.The three cases on 28 April 2007,9 April 2009,and 29 March 2015 fail to be predicted without the Satellite-RH assimilation as their MABLs have both warming and drying,drying,and warming biases,respectively.Intercomparisons and evaluations show that Method-RH has the best overall performance of the three methods in terms of the forecast of sea fog and MABL structures as only Method-RH can fully or partially address all the bias scenarios in forecasting sea fog.Compared with Method-q,Method-RH produces more well-defined sea fog areas by adding a smaller amount of moisture as well as decreasing the temperature.Compared with Methodt,Method-RH enlarges the sea fog areas by increasing the amount of moisture in addition to the cooling.

Convective Rainfall in Amazonia and Adjacent Tropics

Hourly rainfall estimates from integrated satellite data are used to build a dynamically based climatology of convectively generated rainfall across South America, including tropical, sub-tropical and oceanic regions. Herein, we focus on 0S to 15S, including greater Amazon and NE Brazil leeward of the South Atlantic Ocean. Emphasis is placed on rainfall resulting from organized convective regimes, which are known to produce the majority of seasonal rainfall in various parts of South America and other continents. The statistical characteristics of individual events are quantified and examined with respect to regional atmospheric conditions. Among the factors considered are steering winds and wind shear, convective available potential energy (CAPE), sea and land breezes, and the occurrence of transient disturbances such as Kelvin Waves and Easterly Waves. Forcing and convective triggering mechanisms are inferred from the diagnosis of systematic patterns as evidenced in the continental diurnal cycle and longer periods of natural variability. The episodes of organized convection are analyzed in terms of their duration, span, phase speed, starting and ending time, starting and ending longitude, month and year through frequency distribution analysis. Most episodes of organized convection tend to move westward across the Amazon Basin. Descriptive statistics indicate average phase speed of westward and eastward episodes of convection in the Amazon basin at -11.8 m.s-1 and 13.0 m.s-1, respectively. Eastward propagating systems are influenced by northeastward moving cold fronts in Southern South America and tend to trigger and to organize convection across the Amazon Basin. Hourly rainfall analyses indicate that convection over the Amazon region is often organized.

Convective Rainfall Systems in the La Plata Basin

Hourly rainfall estimates from integrated satellite data are used to build a dynamically based climatology of convectively generated rainfall across the La Plata Basin in South America and adjacent oceans. Herein, the focus of this manuscript is on 20S to 35S, including the Andes cordillera. Emphasis is placed on rainfall resulting from organized convective regimes which are known to produce the majority of seasonal rainfall in Southern South America and other continents. The statistical characteristics of individual events are quantified and examined with respect to regional atmospheric conditions. Among the factors considered are steering winds and wind shear, convective available potential energy (CAPE), localized sensible and latent heat sources over mountains and wetlands (Chaco), and the occurrence of baroclinic waves such as mid-latitude jet stream transient disturbances. Forcing and convective triggering mechanisms are inferred from the diagnosis of systematic patterns as evidenced in the continental diurnal cycle and longer periods of natural variability. The diurnal cycle of rainfall is especially informative with respect to the frequency and phase of rainfall associated with long-lived propagating rainfall “episodes”. Similar to findings in tropical northern Africa and tropical northern Australia, there is a strong presence of organized convection, which can propagate zonally hundreds to thousands of km as a coherent sequence of mesoscale convective systems. Convective triggering is often associated with elevated terrain, the Andes, and the La Plata basin region, which is especially rich in moist static energy. The passage of baroclinic waves over the Andes is consistent with eastward propagating clusters of convection, within which westward-propagating systems also reside. These organized convective systems over the La Plata Basin are analyzed with hourly rainfall estimates with CMOPRH method. Rainfall estimates at 8-km spatial resolution were obtained between December 2002 and June 2008. Very few data are missing so it is one of the most complete, longest and highest resolution data sets available to date that allows a comprehensive description of spatial and temporal distribution of convection from its hourly to interannual variability over the region. In this work, diurnal, intra and inter seasonal and interannual cycles are obtained and examined in the light of episodes of organized convection. Daily, monthly and yearly spatial patterns of rainfall accumulation over the La Plata Basin region vary both inter- and intra-seasonally and are forced by underlying dynamic and thermodynamics mechanisms. Time-longitude diagrams of CMORPH hourly rainfall are used to describe the genesis, structure, longevity, phase speed and inferences of the underlying dynamics and thermodynamics of episodes of organized convection. The episodes of organized convection are analyzed in terms of their duration, span, phase speed, starting and ending time, starting and ending longitude, month and year through frequency distribution analysis. Most episodes of organized convection move eastward across the La Plata Basin with variable phase speeds. Basic descriptive statistics indicate that the La Plata eastward propagating average phase speed is 13.0 m·s-1.