Annual report on studies of space/time variability of marine boundary layer characteristics

March 1988.Includes bibliographical references.Contract #N00014-886-C-0459

Diurnal cycle of tropical deep convection examined using high space and time resolution satellite data

September 1997.Includes bibliographical references.Infrared (IR) and visible (VIS) satellite data from GMS-4 with 5-km spatial and 1-hr temporal resolution was used to examine the diurnal cycle of deep convection over a sector of the tropical west Pacific warm pool (WP) bounded by 140°-180°E, 0°-20°N. Data were analyzed for 45 days of summer from 22 June 1994 - 5 August 1994 (JJA) and for 65 days of winter between 28 November 1994 – 31 January 1995 (NDJ). The synoptic backdrop for JJA was characterized by the monsoon trough, oriented northwest to southeast through the WP. Convection was largely focused along the trough. During NDJ, convection was concentrated within 5° latitude of the intertropical convergence zone (ITCZ) which was oriented east to west near the equator. December 1994 was characterized by an active phase of the intraseasonal oscillation (ISO) while January 1995 coincided with an inactive phase. Deep convective cloud was identified in IR imagery using brightness temperature (TBB) threshold techniques. Cloud forms associated with deep convection showed two distinct diurnal modes representing deep convection (TBB ≤ -60°C) and stratiform cirrus (-52°C ≤ TBB ≤ -23°C). Clouds with TBB warmer than -60°C and colder than -53°C comprised a mixed deep convection and cirrus anvil regime from the satellite's perspective with a diurnal cycle reflecting both modes of variability. The diurnal variation of cloud in these regimes was consistent for all time periods and for two tropical storms which occurred in the WP during December 1994. Based on these results and on previous studies, a -65°C cloud-top TBB threshold was chosen to isolate pixels containing active, deep convection. Spectral analysis of time series constructed from hourly cold cloud (≤ -65°C) pixel counts revealed a powerful diurnal cycle of deep convection significant at the 95% confidence level during JJA and NDJ. Composited hourly statistics of fractional areal cloud cover documented a 0500-0600 LST maximum with a 1500-1900 LST minimum of convection for both seasons. The ratio of maximum to minimum areal cold cloud coverage was greater than 2: I. A significant bi-diurnal cycle was evident in both JJA and January 1995. The bi-diurnal peak was strongest in the near-equatorial region during JJA. No semi-diurnal (spectral) peak occurred during either season. This suggests that semi-diurnal atmospheric tides do not strongly influence convection in the WP. Three objective analysis techniques were developed to analyze the relation of tropical cloud cluster structure to the daily spatial and temporal variation of deep convection. The first technique identified cold cloud intervals, called line clusters, in each image. These line clusters represented a characteristic horizontal dimension for cloud clusters of various sizes. Results showed that the diurnal cycle of convective rainfall with an early morning maximum was disproportionately dominated by the largest ~ 10% of clusters for each time period. While the number of large clusters increased only slightly throughout nocturnal hours, the area of cold cloud associated with these systems expanded dramatically. An algorithm called threshold initiation showed that all scales of organized, intensifying deep convection existed at all times of day and night. In addition, the early morning peak was composed primarily of building convection. Conditional recurrence probabilities of line clusters were computed at 24 and 48 hour intervals. Results for JJA and December 1994 revealed that when early morning convection occurred at any location, the same region contained convection the next morning nearly half the time. Convection was less likely at the 48 hour point. These results do not support diurnal theories based on sea surface heating, afternoon initiation of convection and nocturnal evolution of mesoscale convective systems. Findings indicate that the diurnal cycle of deep convective cloud is driven by the internal variation of large clusters. Clusters that exist into or form during the night, grow spatially larger and more intense. Some results support direct radiative forcing of clouds and large scale clear region radiative destabalization as possible contributors to diurnal convective variability. However, all findings are consistent with the work of Gray and colleagues that emphasizes the role of day-night variations in net tropospheric cooling in clear and longwave cooling in cloudy versus clear regions as an explanation of the observed daily variation of tropical convective rainfall.Research supported under the Center for Geosciences, Phase II at CIRA/CSU by DoD grant no. DAAH04-94-G-0420

Remote sensing of water vapor over land using the advanced microwave sounding unit

Includes bibliographical references.Water vapor is a fundamentally important variable in the atmosphere for making accurate forecasts. Its global distribution is a challenge to determine and can change rapidly in both space and time. Several ground and space based methods are currently employed to determine its spatial and temporal variability. The microwave spectrum is very useful for remote sensing due to its ability to penetrate through clouds at most frequencies. Microwave satellite sensors have been used to retrieve atmospheric state parameters for several decades, however the retrievals of certain parameters have not been performed satisfactorily over land thus far. Retrievals rely on the ability to extract the atmospheric state from the upwelling radiation, most of which comes from emission from the surface. Knowing the surface emissivity to a high degree of accuracy is essential for calculating the land surface temperature, however it is also important because this emission must be removed in order to retrieve the atmospheric parameters desired. Land type, vegetation, snow, ice, rain, urbanization effects, and many other factors have an effect on the aggregate emission within each viewing scene and results in a strong sensitivity and variability of microwave emissivity on small scales. A physically based iterative optimal estimation retrieval has been implemented to retrieve atmospheric parameters from the Advanced Microwave Sounding Unit (AMSU). This retrieval is based on the method of Engelen and Stephens (1999). The retrieval uses a first guess of water vapor and temperature profiles (currently from radiosondes, but will soon be from GDAS), and uses a first guess of emissivity at each of five frequencies (from the MEM). The retrieval was run with a highly accurate first guess in order to detect bias, and the total precipitable water amounts were validated against a radiosonde match-up dataset. The match-up showed fair agreement between the radiosondes and the retrieval (within 20%), however a systematic bias was detected due mostly to coastline contamination. Data from the Global Positioning System (GPS) was also used to validate the total precipitable water, however the results showed less agreement than the radiosonde results (variations of ~20-35%). Most of this disagreement stemmed from geographical co-location differences. The analytical Jacobian was also examined to determine the sensitivities of all channels to the state vector parameters. This enables any retrieval user to pick a channel configuration that gives the desired sensitivities. Vertical profiles of water vapor sensitivities at four varying emissivities were investigated. Sensitivities of water vapor to emissivity were also examined at three distinct atmospheric pressure levels. The Jacobian determined that water vapor is able to be detected throughout a vertical column with adequate skill, although problematic areas occurred between 600 and 800 mb as the emissivity approached unity (e>0.99) for a wet atmospheric case. These results give confidence that AMSU can detect TPW over land for both weather forecasting and for climate studies. The current capabilities may be improved further once bias sources are dealt with satisfactorily.Research was supoprted in part by Cloud Sat at NASA-Goddard under Contract Agreement NAS5-99237, the DoD Center for Geosciences/Atmospheric Research at Colorado State University under the Cooperative Agreement DAAD19-02-2-0005 with the Army Research Lab, and by the Joint Center for Satellite Data Assimilation (JCSDA) Program via NOAA grant NA17RJ1228#15 under CIRA's Cooperative Agreement with NOAA

Study of tropical cyclone structural evolution, A

Includes bibliographical references.The destructive potential of a tropical cyclone is highly dependent on both the intensity and size of the storm. There has been extensive research done on intensity and intensity change, but far less work has focused on tropical cyclone structure and structural changes. The recent highly active Atlantic tropical seasons reemphasize the need for a better understanding of tropical cyclone structural evolution. This is particularly true of the 2005 season which produced a number of storms, such as Katrina, Rita, and Wilma, that not only became extremely intense, but also grew substantially in size during intensification. In contrast to these giants are the storms such as Hurricanes Charley (2004) and Emily (2005), which reached equal intensity, but remained fairly small in size. The goal of this study is to gain a better understanding of what causes these different structural evolutions in tropical cyclones. The inner core (0-200 km) wind-fields of Atlantic and Eastern Pacific tropical cyclones from 1995-2005 from aircraft reconnaissance flight-level data is used to calculate the low-level inner core kinetic energy. An inner core kinetic energy-intensity relationship is defined which describes the general trend of tropical cyclone inner core kinetic energy (KE) with respect to intensity. However, this mean KE/intensity relationship does not define the evolution of an individual storm. The KE deviations from the mean relationship for each storm are used to determine the cases where a storm is experiencing significant structural changes. The evolution of the KE deviations from the mean with respect to intensity indicates that hurricanes generally either grow and weaken or maintain their intensity, or strengthen but do not grow at the same time. The data is sorted by the state of intensification (intensifying, weakening, or maintaining intensity) and structure change (growing or non-growing), defining six sub-groups. The dynamic, thermodynamic, and internal conditions for the storm sub-groups are analyzed with the aid of statistical testing in order to determine what conditions are significantly different for growing versus non-growing storms in each intensification regime. These results reveal that there are two primary types of growth processes. The first is through eyewall replacement cycles, an internally dominated process, and the second via external forcing from the synoptic environment. As a supplement to this study, a new tropical cyclone classification system based on inner core KE is presented as a complement to the Saffir-Simpson hurricane scale.Funding for this research was sponsored by CIRA activities and participation in the GOES Improved Measurement Product Assurance Plan (GIMPAP) under NOAA cooperative agreement NA17RJ1

Forecasting rain events in the southern Great Plains using GPS total precipitable water amounts

Includes bibliographical references.Funding for this research is supported by an American Meteorological Society Graduate Student Fellowship, sponsored by the National Oceanic and Atmospheric Administration's (NOAA) Office of Global Programs, by NOAA under cooperative agreement NA17RJ1228 with CIRA, and by the Research and Scholarly Programs fund at Colorado State University (CSU)

Regional water vapor distribution and its clear sky longwave radiative effects

Fall, 1994.Bibliography: pages 86-89.Sponsored by NASA NAGW-2700

Estimation of Big Thompson flood rainfall using infrared satellite imagery

December, 1978.Includes bibliographical references.Sponsored by NSF ATM-8415127

Atlas of radiation budget measurements from satellites (1962-1970)

December 1974.Includes bibliographical references

Observed and calculated properties of mid-level, mixed-phase clouds

Includes bibliographical references.The University of Wyoming King Air research aircraft was flown into five mid-level clouds that formed over the western Great Plains during the Ninth Complex Layered Cloud Experiment (CLEX-9). Four of the clouds were mixed-phase. This study presents the direct observations made of these clouds as well as the cloud properties that were derived from these observations. In particular, profiles of temperature, water vapor mixing ratio, liquid water content (LWC) and ice water content (IWC) are shown. These profiles were used to calculate profiles of latent heating rate, and long- and shortwave radiative heating rate. In-cloud temperatures were observed between +2 °C and -25 °C. Maximum horizontally averaged LWC and IWC values were between 0.04 - 0.28 g m-3 and 0 - 0.16 g m-3 respectively. Cloud depths ranged from 248 m to 3106 m, with cloud bases between 2.9 and 5.6 km above mean sea level. Direct observations of ice particles made through the use of 2D-C and 2D-P optical imaging probes were analyzed using the methods of Heymsfield et al. (2002) to account for departures from sphericity, which reduces the observed ice water content by as much as 95%. These methods were also used to fit the observed ice particle size distribution into a modified gamma distribution equation, from which the ice particle effective radii were determined. Knowledge of the ice particle effective radii, plus observations of the liquid droplet effective radii made by a Forward Scattering Spectrometer Probe, were used with the profiles of LWC and IWC to calculate liquid and ice water paths and optical depths of these clouds. Ice particle size distributions and profiles of IWC show evidence of growth by the Wegener-Bergeron-Findeisen mechanism and aggregation. This data was input into a simple model to calculate the relative importance of subsidence, radiation, entrainment and precipitation in affecting cloud lifetimes. Results of this model show that subsidence and precipitation are the most important processes. It is also shown that the passage of potential vorticity anomalies may be intricately linked to the lifetimes of isolated, non-frontal and non-orographic mid-level clouds. A selection of previous studies was examined in light of these results to develop a consistent picture of the lives of midlevel clouds. The results of this study are shown to be similar to the results of previous studies of mid-level clouds, particularly those that took place over the continental United States.This work was supported by the NASA CloudSat Data Processing Center grant number NAS5-99237. Partial support was also provided by the DoD Center for Geosciences/Atmospheric Research under Cooperative Agreement from the Army Research Laboratory (DAAD01-98-2-0078, DAAD19-01-2-0018 and DAAD19-02-2-0005)

Objective estimation of tropical cyclone wind structure from infrared satellite data

Includes bibliographical references.Given the destructive nature of tropical cyclones, it is extremely important to provide quality estimates of intensity, as well as wind structure. The Dvorak technique, and an automated version, the Objective Dvorak Technique (ODT) use a method of identifying cloud characteristics from satellite images (visible and infrared), to provide estimates of current storm intensity. However, these IR techniques provide no information on the extent or location of damaging winds. Estimates of wind structure via alternate methods have significant disadvantages. Gathering data using aircraft is expensive; therefore storms are flown only if they are an immediate threat to the U.S. AMSU algorithms for estimating wind structure have proven successful, however the instruments fly aboard polar-orbiting satellites, which only pass over the tropics twice a day, and are not contiguous at or near the equator. It is apparent that an alternate method of estimating wind structure is necessary; one in which data coverage is continuous. While IR data has historically been used to estimate intensity, the goal of this research is to extend the use of IR data to estimate wind structure. Theoretically, there should be a solid relationship between deep convection and the extent of damaging winds. The database for this work includes aircraft reconnaissance data from 91 Atlantic and E. Pacific storms flown during the 1995-2003 seasons as ground truth, in combination with GOES IR imagery, and storm best track information. Using multiple linear regression techniques, with predictors derived from the IR data, a radius of maximum wind can be estimated, as well as, more accurately, the symmetric tangential winds at a radius of 200 km (size parameter). These estimated parameters are then fit to a modified combined Rankine vortex model to reconstruct the entire symmetric wind field. Given the storm motion vector, and researched relationships between storm motion and wind asymmetries, the asymmetric part of the wind field can be calculated and added to the symmetric part to provide an estimation of the entire tropical cyclone wind field.Funding for this research was primarily sponsored by CIRA Activities and Participation in GOES I-M Produce Assurance Plan under NOAA cooperative agreement NA17RJ1228. Further support was provided by Improvement in Deterministic and Probabilistic Tropical Cyclone Surface Wind Predictions under NOAA cooperative agreement NA17RJ1228