INTRODUCTION.

Since the first WSR-88D was installed in Twin Lakes, OK, in 1966, it was evident that the radar was detecting non-meteorological targets in the atmosphere in both clear air and precipitation modes. We began our work with the WSR-88D in the spring of 1992 when the first unit was installed on the northern coast of the Gulf of Mexico at Dickinson, TX, (KHGX). It was apparent that the radar readily detected bird movements in the atmosphere during the day and at night, and it was obvious that these biological reflectors seriously biased the velocity azimuth displays (VAD) and VAD wind profiles generated by the WSR-88D. Since that time we have gathered thousands of hours of WSR-88D products showing bird movements associated with migration, roosting, and feeding behavior. The imagery that follows relates to migratory and roosting movements.

In spring when return flow conditions prevail over the Gulf of Mexico, flocks of migrating birds (e.g., songbirds, shorebirds, herons) arrive on the northern coast after crossing the Gulf. From mid-March to late-May these almost daily pulses of trans-Gulf migrations (TGM) usually reach the northern coast during the daylight hours and the flights are nearly finished by nightfall. After moving inland to suitable habitats the birds land. Weather conditions permitting, most of the migrants take off from these stopover areas and resume their migration 30 to 45 minutes after dark. This phase of the movement is called the EXODUS from stopover areas.

With respect to the imagery that follows, the first two sets of images relate to the TGM phase of a daily migratory flight. Both base reflectivity and base velocity images are included. ARRIVAL IMAGERY

The second two sets of images relate to the EXODUS phase from stopover areas inland from the coast - one set for base reflectivity and one set for base velocity. EXODUS REFLECTIVITY AND VELOCITY IMAGERY

The fifth set of images shows the VAD wind profile as birds begin the EXODUS phase. EXODUS VAD IMAGERY

The sixth set of four images shows the departure of Purple Martins from roost sites near dawn and sunrise. These images taken from the internet are provided through the courtesy of WSI Corporation. These large swallows gather into roosting assemblages of hundreds of thousands of birds every night following the breeding season. By late-August most of the birds have departed these roost sites and moved to their wintering grounds in South America. ROOST IMAGERY

Additional images of Purple Martins departing from roost sites at each end of the Lake Pontchartrain Causeway in southeast Louisiana and on the Dauphin Island Causeway in southwestern Alabama can be found in the archived material provided by Robert Alan Steenburgh. The data are also provided in a prod.dat file (for possible viewing on a PUP) and a full directory of individual products that can be displayed using GEMPAK, or N-AWIPS software (e.g., GARP).LAKE PONTCHARTRAIN IMAGERY AND DATA

IMAGERY SETS:

ARRIVAL IMAGERY. These 12 base reflectivity images in precipitation mode (26-27 April 1997, 1324-0023 UTC) from the Lake Charles, LA, (KLCH) WSR-88D show the arrival of a trans-Gulf migration on the northern Gulf coast of southwestern Louisiana. At 1324 UTC echoes from flocks of migrants (small blue dot echoes) can be seen behind the band of heavy weather moving offshore. From 1324 UTC the movement increases in intensity until 1820 UTC when the maximum reflectivity of 20 dBZ is reached. Thereafter the movement decreases and by 0023 UTC most of the trans-Gulf migration has arrived on the northern coast. The direction of this flight can be seen on the corresponding base velocity images. Surface and 850mb charts depict the weather conditions during this arrival period. (26/1200 UTC:850mb and Surface. 27/0000 UTC:850mb and Surface.)

Animation of Arrival Base Reflectivity Images

These 12 base velocity images (26-27 April 1997, 1324-0023 UTC) from the Lake Charles, LA, (KLCH) WSR-88D show the arrival of a trans-Gulf migration on the northern Gulf coast of southwestern Louisiana. The scattered echoes from flocks of trans-Gulf migrants behind the band of weather in the 1324 UTC image have inbound velocities greater than 30 kts. In the 2122 UTC image the majority of flocks have inbound and outbound velocities of 40-50 kts. At 2300 UTC (the time of the radiosonde release from the Lake Charles NWS station), inbound and outbound velocities from migrating birds were in the 30-40 kt category, significantly faster than the 850-mb winds (see associated 850-mb map of winds for 0000 UTC). Surface and 850mb charts depict the weather conditions during this arrival period. (26/1200 UTC:850mb and Surface. 27/0000 UTC:850mb and Surface.)

Animation of Arrival Base Velocity Images

EXODUS REFLECTIVITY AND VELOCITY IMAGERY. These 14 base reflectivity images in clear air mode (28-29 April 1997, 2314-1219 UTC) show the exodus of trans-Gulf migrants from stopover areas around the Lake Charles, LA, (KLCH) WSR-88D site and the continuation of nocturnal migration over the station. Typically because source areas to the south are limited by the Gulf, most of the exodus is completed by 0400 UTC when birds are flying toward the N or NE from Lake Charles, but on this night the movement continues until dawn. The reason for this is that on this evening the flight is toward the ENE (see corresponding base velocity images) and source areas to the WSW of Lake Charles are not limited by the Gulf of Mexico. Surface and 850mb charts depict the weather conditions during this exodus period. (29/0000 UTC:850mb and Surface.)

Animation of Exodus Base Reflectivity Images

These 14 base velocity images (28-29 April 1997, 2314-1219 UTC) show the exodus of trans-Gulf migrants from stopover areas around the Lake Charles, LA, (KLCH) WSR-88D site and the continuation of nocturnal migration over the station. These images correspond to the previous 14 base reflectivity images. Note that the exodus begins about 0121 UTC and is directed toward the east. In subsequent images the targets with the fastest base velocities are moving toward the ENE and this corresponds to the 850-mb winds aloft (see associated weather images). Surface and 850mb charts depict the weather conditions during this arrival period. (29/0000 UTC:850mb and Surface.)

Animation of Exodus Base Velocity Images

EXODUS VAD IMAGERY. These 14 VAD vertical wind profile images (28-29 April 1997, 2314-1209 UTC) show the beginning of the exodus of migrant birds from stopover areas in southwestern Louisiana. Each image covers about 1.5 hours of profiles and is labeled with the time of the last profile plotted. The beginning of the exodus is at 0121 UTC. Note the direction of the VAD winds at the 1000 ft level from 2314 until 0121 UTC (first four images). At 0121 UTC the exodus of migrants begins and the VAD shows a change in wind direction and an increase in velocity. The changes are the result of birds being selected as reflectors for the generation of VAD winds. The vertical extent of the wind barbs reflects the altitudinal distribution of migrating birds in the atmosphere. Surface and 850mb charts depict the weather conditions during this arrival period. (29/0000 UTC:850mb and Surface.)

Animation of Exodus VAD Images

Animation of Pontchartrain Base Reflectivity Images

Animation of Pontchartrain Spectrum Width Images

Animation of Pontchartrain VIL Images