Paul W. Stackhouse

The radiative budgets of a tropical mesoscale convective system during the EMEX‐STEP‐AMEX experiment: 2. Model results

This paper describes calculations of the spatial and temporal variation of the radiation budget of a tropical mesoscale convective system (MCS). A combination of cloud model simulations, radiation model simulations, and analyses of observations obtained during the Equatorial Mesoscale Experiment (EMEX), the Stratosphere-Troposphere Exchange Program (STEP), and the Australian Monsoon Experiment (AMEX) are used to obtain these heating rates. The two-dimensional version of the Colorado State University regional atmospheric modeling system is used to simulate a tropical MCS that occurred during EMEX mission 9 on February 2, 1987. The simulation is shown to broadly agree with the observations reported in a related paper. The spatial radiative heating distributions derived from a two-stream radiative transfer model corresponding to the mature stage of the simulated cloud system indicate that significant horizontal inhomogeneities exist. According to the model results the effects of the MCS are to (1) increase in the infrared emission to the surface and to decrease in the net infrared energy loss from the atmosphere relative to the clear sky emission and (2) change the transmission of solar flux to the surface, the shortwave albedo of the atmosphere, and the solar absorption in the atmosphere. The results show how the MCS significantly reduces the solar flux to the surface relative to the clear sky values and that the largest reduction occurs under the convective portions of the mature MCS. (3) The MCS creates a total (solar plus infrared) radiative warming in the atmosphere relative to the surrounding clear sky. The value of this total heating is governed by both infrared and solar absorption. Vertical profiles of this heating show the dominance of infrared cooling near cloud top and infrared heating inside and near cloud base. The shortwave heating rate can also be as large as the infrared cooling near the cloud top region of the tropical MCS, especially at a local noon. (4) The temporal changes in radiation profiles also demonstrate how the MCS modulates the radiation budget of the atmosphere. Specifically, the total radiation energy loss of the entire two-dimensional domain of the model atmosphere decreases and eventually becomes positive as the cloud system decays, becomes a stratiform in nature, and fills the domain. This change in the column divergence of flux translates into a total column radiative heating rate of approximately 1.7 K/d (relative to the clear sky radiative cooling rate). The solar component of this domain heating tends to be concentrated in the upper troposphere, whereas the infrared component of the heating is spread over the lower and middle troposphere. These results also show how tropical mesoscale cloud system provides an effective radiative heat source for the tropical atmosphere.

The radiative budgets of a tropical mesoscale convective system during the EMEX‐STEP‐AMEX experiment: 1. Observations

This paper is the first of a series of two that aim to describe the spatial and temporal variation of the radiative heating associated with tropical mesoscale convective systems (MCSs). This paper describes the analysis of data collected in and around a tropical cloud cluster system studied as part of the Equatorial Mesoscale Experiment (EMEX). The data analysis indicates that the cluster originated off the northern coast of Australia along the midlevel monsoon trough and lasted approximately 12 hours. The system moved with a velocity of about 12 m/s toward the northeast and the low-level surface northwesterly flow at the vicinity of the premonsoon trough area seems continuously to feed the EMEX 9 cloud cluster with energetic warm, moist equatorial air. Data obtained from aircraft penetrations show features similar to tropical MCSs reported elsewhere (such as an area of strong to moderate convection surrounded by a broad region of stratiform precipitation, radar echo bright band in the stratiform region, “onion” type sounding behind the convective region). The vertical structures of the EMEX 9 cloud cluster also contain two types of imbedded convection: an upright vertical structure and a pronounced rearward slope (approximately 17°), having a vertical extent of 14.5 km and above and a horizontal scale of about 40 km. The cloud base and cloud top altitude in the stratiform region are estimated to be of the order of 4.8 km and 15 to 16 km, respectively. The composite aircraft shortwave radiation data from the stratiform region show a significant attenuation of shortwave flux through the cloud (the estimated transmission is 14% at cloud base). The upward and downward solar flux profiles are almost parallel to each other in the atmosphere inside and below the cloud base, suggesting very little solar heating in these regions. The upward and downward infrared radiation fluxes measured in the tropical MCS also show little infrared heating above and below the cloud cluster.

The NASA GEWEX surface radiation budget project: Dataset validation and climatic signal identification

The NASA GEWEX-SRB (Global Energy and Water cycle Experiment - Surface Radiation Budget) project has produced and archived shortwave and longwave radiative fluxes at the top of atmosphere (TOA) and the Earths surface at a 1° × 1° resolution continuously for a time span of 24.5 years from July 1983 to December 2007. The latest version of the data in archive is Release 3.0 and is available as 3-hourly, daily and monthly means. Through August, 2011, the Baseline Surface Radiation Network (BSRN) archive has 5969 site-months of ground-measured data from 52 sites around the globe. We first performed quality-check on the original BSRN data and, then processed the data to produce 3-hourly, 3-hourly-monthly, daily and monthly means. The SRB-BSRN comparisons show generally good agreement for both the shortwave and longwave downward fluxes at the Earths surface. It is found that signals of large-scale climatic variation, such as El Nino Southern Oscillation, can be identified through EOF analysis. Polynomial fitting of order 3 for Southern and Northern Hemispheric and global mean downward shortwave fluxes from 1984 to 2007 shows variability consistent with global dimming through 1980s and brightening thereafter.The NASA GEWEX-SRB (Global Energy and Water cycle Experiment - Surface Radiation Budget) project has produced and archived shortwave and longwave radiative fluxes at the top of atmosphere (TOA) and the Earths surface at a 1° × 1° resolution continuously for a time span of 24.5 years from July 1983 to December 2007. The latest version of the data in archive is Release 3.0 and is available as 3-hourly, daily and monthly means. Through August, 2011, the Baseline Surface Radiation Network (BSRN) archive has 5969 site-months of ground-measured data from 52 sites around the globe. We first performed quality-check on the original BSRN data and, then processed the data to produce 3-hourly, 3-hourly-monthly, daily and monthly means. The SRB-BSRN comparisons show generally good agreement for both the shortwave and longwave downward fluxes at the Earths surface. It is found that signals of large-scale climatic variation, such as El Nino Southern Oscillation, can be identified through EOF analysis. Polynomial fitti...

NASA/GEWEX Surface Radiation Budget: Integrated Data Product With Reprocessed Radiance, Cloud, and Meteorology Inputs, and New Surface Albedo Treatment

The NASA/GEWEX Surface Radiation Budget (SRB) project produces shortwave and longwave surface and top of atmosphere radiative fluxes for the 1983-near present time period. Spatial resolution is 1 degree. The current Release 3.0 (available at gewex-srb.larc.nasa.gov) uses the International Satellite Cloud Climatology Project (ISCCP) DX product for pixel level radiance and cloud information. This product is subsampled to 30 km. ISCCP is currently recalibrating and recomputing their entire data series, to be released as the H product, at 10km resolution. The ninefold increase in pixel number will allow SRB a higher resolution gridded product (e.g. 0.5 degree), as well as the production of pixel-level fluxes. Other key input improvements include a detailed aerosol history using the Max Planck Institute Aerosol Climatology (MAC), and temperature and moisture profiles from nnHIRS.The NASA/GEWEX Surface Radiation Budget (SRB) project produces shortwave and longwave surface and top of atmosphere radiative fluxes for the 1983-near present time period. Spatial resolution is 1 degree. The current Release 3.0 (available at gewex-srb.larc.nasa.gov) uses the International Satellite Cloud Climatology Project (ISCCP) DX product for pixel level radiance and cloud information. This product is subsampled to 30 km. ISCCP is currently recalibrating and recomputing their entire data series, to be released as the H product, at 10km resolution. The ninefold increase in pixel number will allow SRB a higher resolution gridded product (e.g. 0.5 degree), as well as the production of pixel-level fluxes. Other key input improvements include a detailed aerosol history using the Max Planck Institute Aerosol Climatology (MAC), and temperature and moisture profiles from nnHIRS.

FIRE in the Classroom

This paper describes a classroom project that exposes students to research data collected during the Cirrus II First ISCCP (International Satellite Cloud Climatology Program) Regional Experiment Information Systems Office from Parsons, Kansas, during November and December 1991. The data employed in this project were primarily those obtained from a Michelson interferometer. The students were assigned a number of tasks that were aimed at (i) providing them with a basic understanding of a Michelson interferometer and, most importantly, an appreciation of the importance of calibration, (ii) understanding the spectral distribution of clear-sky emission and identifying major gaseous absorption features, (iii) understanding the effects of cirrus clouds on the emission spectrum, and finally (iv) learning how these spectra may be used to derive certain properties of the clouds and in so doing appreciate some of the limitations and ambiguities of this particular type of remote sensing.