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Chronis, Themis

Publications and source records attributed to Chronis, Themis.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

The WRF Lightning Forecasting Algorithm: Sensitivities to Microphysics and Boundary Layer Physics Schemes

As with WRF model simulated convection in general, LFA output is sensitive to cloud and PBL physics. WRF convection is also sensitive to model initialization uncertainties and unresolved errors.  Large sensitivity exists in HRRR-like Thompson microphysics and PBL, for which original LFA calibration constant needs to be multiplied by 1.13 to give proper FRD amplitudes. Thompson microphysics scheme also shows poorest correlations relative to reference data, suggesting low predictability of HRRR LFA output. Need to validate HRRR LFA against GLM observations.

weather prediction↗
NASA NTRS2019

Diurnal Cycle of ASCAT-Identified Cold Pools and Associated Convective Systems in the Maritime Continent and South China Sea

Mesoscale convective cold pools are known to alter the turbulent air-sea fluxes in the regions of active convection such as maritime tropics. Satellite-based Ocean Vector Wind instruments have proven to be useful in observing these mesoscale outflows corresponding to convective cold pools. A new storm-centric, tensor-based wind-gradient identification algorithm identifies gradients associated with convective cold pools and other boundaries such as land-sea breeze fronts. We term these as Gradient Features or GFs; analyzed over tropical oceans (2007-2018) using horizontal winds from Advanced Scatterometer (ASCAT-A).

Nesbitt, Stephen W.↗
NASA NTRS2017

The Cyclone Global Navigation Satellite System (CYGNSS) - Analysis and Data Assimilation for Tropical Convection

Cyclone Global Navigation Satellite System (CYGNSS): a constellation of 8 micro-satellite observatories launched in November 2016, to measure near-surface oceanic wind speed. Main goal: To monitor surface wind fields of the Tropical Cyclones' inner core, including regions beneath the intense eye wall and rain bands that could not previously be measured from space; Cover 38 deg S -38 deg N with unprecedented temporal resolution and spatial coverage, under all precipitating conditions Low flying satellite: Pass over ocean surface more frequently than one large satellite. A median(mean) revisit time of 2.8(7.2) hrs.

CYGNSS↗
NASA NTRS2017

Using Buoy and Radar Data to Study Sudden Wind Gusts Over Coastal Regions

Significant sudden wind gusts can pose a threat to aviation near the coastline, as well as small (sailing) boats and commercial ships approaching the ports. Such cases can result in wind speed changes of more than an order of magnitude within 5 minutes, which can then last up to 20 minutes or more. Although the constellation of scatterometers is a good means of studying maritime convection, those sudden gusts are not easily captured because of the low time resolution. The National Data Buoy Center (NDBC) provides continuous measurements of wind speed and direction along the US coastal regions every 6 minutes. Buoys are platforms placed at specific places on the seas, especially along coastlines, providing data for atmospheric and oceanic studies. Next Generation Radars (NEXRADs), after the recent upgrade of the network to dual-pol systems, offer enhanced capabilities to study atmospheric phenomena. NEXRADs provide continuous full-volume scans approximately every 5 minutes and therefore are close to the time resolution of the buoy measurements. Use of single- Doppler retrievals might also provide a means of further validation.

Winds↗
NASA NTRS2017

Using CYGNSS to Observe Convectively Driven Near-Surface Winds in Tropical Precipitation Systems During Madden-Julian Oscillation Events

The Cyclone Global Navigation OKLMA 1411 UTC Satellite System (CYGNSS) is a multi-satellite constellation that launched 15 December 2016. The primary objective of CYGNSS is to use bistatic Global Positioning System (GPS) reflectometry to accurately measure near-surface wind speeds within the heavily raining inner core of tropical cyclones. CYGNSS also features rapid revisit times over a given region in the tropics - ranging from several minutes to a few hours, depending on the constellation geometry at that time. Despite the focus on tropical cyclones, the ability of CYGNSS to provide rapid updates of winds, unbiased by the presence of precipitation, has many other potential applications related to general tropical convection.

Convection↗